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An Introduction to the Practical Use of GRASS 6.0

1. 10 Restructuring vector features 62 10 1 New properties of GRASS 6 0 2 0 00 2 2 eee eee ee 62 10 2 Management of vector geometries 2 02 cee ee ee 63 10 2 1 Working with OGR formats 22 as 6 ee ke EM OR wR bee Gre we eee Se 63 10 2 2 Creating geometries out of DBMS 2 20200 4 64 10 2 3 Creating geometries using XY and or XYZ textfle 65 10 3 Managing vector attributes 2 2 2 ee 66 10 3 1 Display attributes 2 624 22 ed eae eee Gea e BERS bee Eeeiw ed ot 67 10 3 2 Adding attributes a ht oe Eee ee ee RE SS ee EE 68 10 3 3 Manipulating vector attributes 2 2 2 2 22220000504 68 11 Working with vector data 70 11 1 Network analysis 0 a 70 11 1 1 Shortest Path Analysis o oo 71 11 1 2 Subnets within a vector network o oao oo e e 00002 eee eae 72 11 1 3 Minimum Steiner Tree Problem 0 00000 e eee 72 11 1 4 Travelling Salesman Problem 2 000002 ees 72 11 1 5 Cost analysis tee he es i Re ee eee ea Qe RR ei RK 72 11 2 Data intersection data overlay dataunion 0 0000 73 11 2 1 Data union 2 200 002 a 73 11 2 2 Dataintersection 0 2 0 00 02 ee 74 1123 Data Cutout oa
2. cylindric Figure 11 Various projection models cylindric conic and azimuthal Depending on the regional situation different models are available see Fig 11 in order to hold the unavoidable distortions as low as possible Cylindric Figure This is the simplest of these figure variants In this figure the map plane at the equator is lain around the globe in order to create a cylinder Meridians and parallels are projected on the plane in such a way that a rectangular grid is created during the phase out This figure is especially used for displaying regions near to the equator A transverse variant is also common in other regions Conic Figure f a cone is lain over the earth and is unrolled in the plane a conic figure is created With the simplest and most frequent application the apex lies on one line with both geographical poles and illustrates the pole nearby Thence the meridians go off in the same angle and the parallels form concentric circles around the intersection The cone contacts the globe on one or two parallels the standard parallels This form is frequently applied to figure regions in the middle latitudes Azimuthal Figure Here the map plane is put on the earth s shape as tangent Imagine a source of light in infinite distance at the opposite side shining through the globe and projecting the shadows of the parallels and meridians on the map plane The basic projections represen
3. Enter False Easting 3500000 3 because 9E is Central Meridian Enter plural form of units meters During parameter input it is sometimes possible to display the projection parameter supported by GRASS via the entry list After the projection parameters have been entered set border coordinates of the project region The boundaries are set to North 5801000 South 5787000 West 3427000 and East 3445000 The GauB Kriger values defined exactly in meters of the topographic maps are attached with 3 zeros For more precision a point is following and afterwards the decimal places see Fig 12 The specification for the resolution raster cell in meters in east west and north south direction is entered in the same entry mask This is the standard raster resolution default of the created location Thus it has no importance for the sharply illustrated sites and vector data and can always be changed with GRASS while working It is recommended to take into consideration that the resolution of raster data has an enormous influence on the necessary calculating and memory requirements GDF Hannover Courses 27 4 5 Creating different project regions in GRASS DEFAULT REGION NORTH EDGE 5801000___ WEST EDGE 3427000___ PROJECTION 99 Other Pro jection GRID RESOLUTION East West North South i Befehlsfenster i Befehlsfenster 2 DEFINE THE DEFAULT REGION IEAST EDGE 13445000__ ZONE 0
4. GDF Hannover Courses 72 11 2 Data intersection data overlay data union 11 2 Data intersection data overlay data union The possibility of intersecting overlaying or unifying vector data is offered in GRASS by the module v overlay Figure 19 VMAPO data Germany To explain the steps we will use simple examples We will use a small VMAPO dataset of Germany This dataset contains political borders inland waterways roads and railways as well as elevation data of Germany which have been reprojected and prepared for this script by GDF Hannover bR The data can also be downloaded at the following website http www gdf hannover de download First the necessary SHAPE data needs to be imported A new location can automatically be created for the data using the projection information available in the SHAPE files create location from within a GRASS session v in ogr pol_borders shp out pol_borders location germany exit Re start with the newly created location grass60 home user grassdata germany PERMANENT v in v in v in v in ogr ogr ogr ogr e dsn e dsn e dsn e dsn 11 2 1 Data union inlandwaterways shp out inlandwaterways roads shp out roads railways shp out railways heightpoints shp out heightpoints Data union is only possible in GRASS if a polygon map is chosen as the input map parameter ainput As an example the political borders are joined
5. WIND Data of the current REGION and the MAPSET projection GRASS 6 0 allows one user to start several GRASS sessions in parallel 2 4 Command structure in GRASS The commands follow a very clear structure in GRASS The type of a command can be recognized by the abbreviation in front of the first period prefix Commands which are independent programs are called modules in GRASS They have self describing names Thus the module for digitalizing raster maps is called r digit In order to convert vector data into raster format the module v to rast is used Table 1 describes the structure of the names of GRASS commands and modules in detail Modules and programs under GRASS Apart from the modules existing in GRASS all Unix Linux programs are available They can be recalled via Shell the command interpreter This is particularly useful if you are interested in programming integrating or modifying your own and or available GRASS modules Even if it may seem difficult to the beginner the ability of a user to program in GRASS provides nearly unrestricted possibilities to realize their own needs and imagination within GIS In addition creating simple Unix Linux Shell scripts is easy to learn GDF Hannover Courses 8 2 5 Help for using GRASS modules Table 1 Structure of the GRASS module names Prefix Function class Meaning of the commands d display For graphical display and visu
6. is still often used in the USA today 4 3 3 Cylindric Projections Table 6 Examples of cylindric map projections Type Mercator Transverse Mercator Projection Figure Normal axial projection Mercator projection rotated 90 Properties Orthomorphic parallel distances Orthomorphic increase proportionally from the equator to the scale Application For navigation and illustrations near Recommended for regions with N S to the equator extent G K UTM basic GDF Hannover Courses 23 4 4 Coordinate systems 4 4 Coordinate systems Having projected the globe or a part of it on a plane a coordinate system must be inserted in order to place 2 or 3 dimensional sites exactly on the map In general global and 2 dimensional and or 3 dimensional coordinate systems are to be differentiated 4 4 1 Global coordinate systems Longitude Latitude The most frequently used global system is that of the longitude latitude and of the height here it concerns no projection The reference planes are the 0 meridian and the equator The earth is therefore divided into 180 longitudes from Greenwich to the East and West Beginning at the equator the earth is also divided into 90 latitudes to the South and North The height is measured at the geocenter but accordingly definition differences are still existing The units of the system can be specified in the sexagesimal Degree Minutes Seconds letter index to
7. GDF Hannover Courses 126 18 7 Creating analog maps with QGIS Peistdbbasssatistectecssssasletisiessesrsstatestessssetatesiticstisesestasierssssstteedtiesssaractetsstesseseestecteseesniosapatetaay o o x PE r i ail p x General Item Title Quantum GIS Legend MapComposer rules Map Map 1 v Layers Group B Gruenflaechen 1 IE Gewaesserlinien EJ Gewaessertla Strassen ICO Dem fill Preview Render Figure 50 Map Composer for creating analog maps from QGIS The so called Map Composer is started via the printer symbol in the toolbar Alternatively the menu entry File gt Print can be chosen Thereupon a white paper is opened to place the map the legend the map title the scalebar etc Papersizes can be chosen freely but a preselection of A4 is selected The hardcopy output will be done with 300 dpi which can be adopted to your needs as well Supported outputformats are currently postscript PNG and SVG However we are curiously looking forward on the development of the QGIS features because these professional developers are dedicates to there work Please do not forget to have a look on our homepage 19 for gathering the latest information GDF Hannover Courses 127 19 Definition of Free Software We maintain this free software definition to show clearly what must be true about a particular software program for it to be
8. GDF Hannover Courses 79 11 6 Digitizing with GRASS Viewpoint Lookout Peak For digitizing the point of interest Lookout Peak the module v digit is started and a new map lookout is created by the option n The imported topographic map tk24 is loaded as the background map Start digitizing module and create new blank map d mon x0 g region rast tk24 v digit n map lookout bgcmd d rast tk24 Now the graphical user interface GUI of the module v digit see figure 20 is automatically started and the TK24 is loaded into the GRASS monitor x0 as the background image Now create a new attribute table including an extra column Name in the v digit GUI using the settings gt Table button see figure 22 bot Symbology Settings Table Background Add new column Create table Figure 22 Creating an attribute table during digitization Afterwards zoom into the map range east of the city of Spearfish and there digitize a point where the point of interest Lookout Peak is located see figure 21 To do this click on the button digitize new point search for the correct point on the map and click on this point with the left mouse button A graphical window is now automatically been opened in which it is possible to assign additional attributes to the point according to the attribute columns defined beforehand In this exercise the category value is supposed to be supplemented by
9. basic structures e continuous appearances gt laminar and unlimited in space e discrete appearances gt definable areas and objects like lines When designing a GIS correct selection of the data structures to be used depends on the standard the spatial resolution the data quantity the original data the planned analysis and more Within GRASS GIS different modules allow conversion between the individual data structures Con tour lines can be stored as vector lines e g in a laminar terrain model in raster format Similarly a map consisting of digital contour lines in vector format can be transformed into a closed terrain surface in raster format by interpolation In this case the quality of the conversion will depend on the resolution of the original data see Fig 3 Raster and vector visualisation of identical spatial objects in GIS 1 greenland 2 water 3 urban area Figure 3 Comparison of raster and vector data types in an identical area 2 2 Data dimensions in GIS Spatial data are mostly available as laminar two dimensional 2D or two and a half dimensional 2 5D data Whenever there is a third parameter e g elevation we call this two and a half dimen sions Descriptions for the sides of bodies e g building surfaces or floor sweeps are the only data actually saved as a 3D system see Fig 4 GDF Hannover Courses 4 2 3 The GRASS database Point Line Area Surface
10. purpose the entry properties in the context menu of the layer view is available in which settings concerning the type of caption the field of categorization and the label display can be changed Furthermore existing meta data can be viewed GDF Hannover Courses 120 18 3 Editing ZA Layer Properties 2 ox Symbology General Metadata Labels Actions Legend type Unique Value X Classification Field Strtypid x Labet a Outine Style Heap Outline color a Outline Width 3 Fill Color o le ma wow _ ox C caves Figure 44 Properties of the vector layer Line width line mode filling examples as well as labeling can be set by this function 18 3 Editing Besides visualizing geodata QGIS also offers editing functions for vector data They can directly be processed in the GRASS location with the GRASS plugin Furthermore processing and creating new shape files is possible GDF Hannover Courses 121 18 3 Editing x pe Laye Sange Pugne Ho T Bad 9888 2 Oak e00 wh fo v eS tow 2 EEE n 4 FA CRASS B i ie SS OCS y Ag av Mo BIC IE c GDF Hannover 2005 P peet aa pansman x mesier ra Figure 45 QGIS in the editing mode of a GRASS vector map 18 3 1 GRASS vectordata It is also possible to digitize with the GRASS plugin As in Figure 45 the editing
11. 2 5 2 58 AFTER COMPLETING ALL ANSWERS HIT lt ESC gt lt ENTER gt TO CONTINUE OR lt Ctr1 C gt TO CANCEL Figure 12 Specifications to the extent of the project region and grid resolution As usual complete the data entry by pressing lt ESC gt lt ENTER gt and you will get back to the begin ning Confirm the creation of the mapset with yes because the name for the mapset was already been indicated An additional confirmation of all the data will finally exit this page Now the project region is installed and active This can be seen because GRASS Prompt is displayed in the Shell The command g region p can be used to verify the region data Here is an example of a GauB Kriger project region projection 99 Transverse Mercator zone 0 datum potsdam ellipsoid bessel north 5801000 south 5787000 west 3427000 east 3445000 nsres 2 5 ewres 2 5 rows 5600 cols 7200 GDF Hannover Courses 28 4 5 Creating different project regions in GRASS 4 5 3 Creating a XY project region Creating an xy location which is necessary for e g intermediate steps for geocoding of non referenced map scans is much more simple because no projection parameters need to be provided After entering A at the question concerning the coordinate system coordinate system for location x y A it is directly be followed by the definition of the border coordinates columns or width rows or height of the project re
12. 42 7 Data export 44 7 1 Exporting raster formats 2 44 4 0 4 45 4 4 44 94 24 te R454 GOS be G44 44 7 2 Exporting vector data 2 2 sk o ote eed Re Se ee RE he 2 eee ESS 45 7 3 EXp rting Sites 4 4 4h RGA de BORA Be OSE ee ORAS ee OR ee SX 45 8 Graphical user interface 46 By GIS Managen e i 2 4 62 5 4 5 Yet B45 ooo Eee EERE H ERE ES SEAS 46 9 Working with raster data 49 9 1 Visualizing rastermaps te kee a ES AS SESE SS SER AS ews 50 9 2 Query of raster cell values and metadata 0 00 0000000 51 9 3 Different raster applications e 0002 eee ee es 53 9 3 1 Calculating transects 2 53 9 3 2 Line of sight analysis dekh dw eee eee RA ER eR De ee 53 9 3 3 Overlapping of individual maps 0 45 05 68 bebe eee ee ee 54 9 3 4 Bufferingrasterdata 2 2 ee ee 55 9 4 Modification and assignment of colortables 220 56 9 5 Map statistics o s s sa ee EE ee a eR oe Se ee Ae a ORR ee SB 57 9 6 Methods for manipulating rastermaps 0 002 eee eee ee 59 9 6 1 Reclassification avee ce hs a Ceee deeds et ea te had ged 59 9 6 2 Masking srao sa socso me koe ee 60 9 7 Digitizing raster dat eine eke eee a OS ORR ae eae RK ERR oe mee 61 GDF Hannover Courses iv Contents
13. Attributes of the attribute table cat gt category values GDF Hannover Courses 94 13 2 Converting vector data into the raster model val gt predefined values Z gt Z coordinate only at points or contour lines If attribute data attr from the attribute table of the vector file are supposed to be assigned to the raster file it is necessary to indicate the respective attribute column The achieved raster exactness depends on the resultion which was set before This can be changed via the module g region GRASS offers the possibility to interpolate sites as raster surfaces The different interpolation methods are discussed in chapter 14 1 GDF Hannover Courses 95 14 Data interpolations One of the applications most frequently used for processing sites is the interpolation of data points regularly or irregularly distributed to a closed data surface In GIS these surfaces are frequently used for modeling and simulations The most widespread and best known example of data interpolation is the generation of a digital terrain model DEM of punctual available elevation data 14 1 Data interpolation into the raster model Generally two different applications are available for interpolating areas e Change of the resolution of raster data Resampling e Filling up of incomplete data interpolation Two GRASS interpolation modules can be used in case of the first mentioned application 1 Nearest Neighbor Met
14. Document and any Warranty Disclaimers provided that you also include the original English version of this License and the original versions of those notices and disclaimers In case of a disagreement between the translation and the original version of this License or a notice or disclaimer the original version will prevail 3 o If a section in the Document is Entitled Acknowledgements Dedications or History the require ment section 20 to Preserve its Title section 20 will typically require changing the actual title TERMINATION You may not copy modify sublicense or distribute the Document except as expressly provided for under this License Any other attempt to copy modify sublicense or distribute the Document is void and will automatically terminate your rights under this License However parties who have received copies or rights from you under this License will not have their licenses terminated so long as such parties remain in full compliance FUTURE REVISIONS OF THIS LICENSE The Free Software Foundation may publish new revised versions of the GNU Free Documentation License from time to time Such new versions will be similar in spirit to the present version but may differ in detail to address new problems or concerns See http Awww gnu org copyleft Each version of the License is given a distinguishing version number If the Document specifies that a particular numbered version of this
15. Factor table for LANDSAT TM bands 1 5 amp 7 i ortho photo Principal components analysis pca program for image process ing Rectifies an image by computing a coordinate transformation for each pixel in the image based on the control points Red green blue rgb to hue intensity saturation his raster map color transformation function Performs contextual image classification using sequential maxi mum a posteriori SMAP estimation displays spectral response at user specified locations in images Targets an imagery group to a GRASS location and mapset Tasseled Cap Kauth Thomas transformation for LANDSAT TM data i vpoints Zero crossing edge detection raster function for image process ing p commands Command Description p out vrml module to output GRASS data in the format of Virtual Reality Modeling Language VRML pg commands Command Description pg postgisdb pg postgisdb Prosecution on next side GDF Hannover Courses 144 Prosecution Command description photo commands Command Description photo 2image photo 2image photo 2target photo 2target photo camera photo init photo init photo rectify photo rectify ps commands Command Description ps map Hardcopy PostScript map output utility r commands Command Description r average Finds the average of values in a cover map within areas assigned the same category value in a user specified
16. GIS systems as well as special formats of other remotesensing sectors GDF Hannover Courses 32 5 1 Importing raster formats Table 7 GRASS modules for importing raster data GRASS Import Module command Raster format r in ascii GRASS ASCII r in bin BIL GMT binary files LANDSAT TM5 r in gdal ARC INFO ASCII Binary GRID BIL ERDAS LAN IMG USGS DOQ JPEG SAR CEOS EOSAT GeoTIFF PPM PNM SDTS DEM GIF PNG see also http www gdal org formats_list htm1 Importing a GeoTiff file The most frequently used module for importing raster data is r in gdal As described in table 7 it is able to read and write many different formats r out gdal As an example we will import a geo referenced map in ERDAS IMG format We have prepared a small ASTERDEM of 30 m resolution based on vector data of the city of Osnabrueck This is available on the GDF Hannover bR website http www gdf hannover de download r in gdal in asterdem30m img out asterdem30m Projection of input dataset and current location appear to match Proceeding with import 100 CREATING SUPPORT FILES FOR asterdem30m COPYING COLOR TABLE FOR asterdem30m With the flag e a possibly necessary spacial extent of the location s definition will be achieved Adapting the current region to the map g region rast asterdem30m p The resulting map can be displayed using the Display Manager d m or w
17. The GIS manager can be started with the command d m amp It also offers some special graphical GDF Hannover Courses 46 8 1 GIS Manager buttons besides the modules which are clearly ordered like in the former Tcl1TkGRASS 4 0 as pull down menus These refer to the sectors of visualization attribute administration digitization and printing and are situated with the pull down menus on the basis of simple symbols beneath the analysis bar Pull down menus for the data analysis GIS Manager Approximately 200 of the 400 modules that are available in GRASS GIS are integrated in the pull down menus This offers the possibility that the most frequently used modules can easily be used with the mouse The menu s structure is the following File contains modules for importing and exporting data and for setting the project GIS makes settings for the projection the work environment and the data management possible Display contains modules for visualizing raster data vector data and sites Raster contains modules for analyzing raster data Vector contains modules for analyzing vector data Image contains modules for analyzing image data Grid3D contains modules for analyzing voxel data 3D raster data Databases contains modules for querying and managing databases Help Help functions Graphical buttons for simple visualization Display Manager The graphical buttons that are situated under the pull down menus allow r
18. a a ee 126 50 Map Composer for creating analog maps from QGIS 127 GDF Hannover Courses viii List of Tables List of Tables 1 Structure of the GRASS module names 9 2 ___ Dimensions of some internationally used ellipsoids and examples of their usage locations 20 3 Some datums with their general application 0000 5s 20 4 _ Examples of azimuthal map projections 2 000002005 23 5 _ Examples of conic map projections 2 ee ee 23 6 _ Examples of cylindric map projections a 23 7___ GRASS modules for importing rasterdata 0002 eee eee 33 8 GRASS modules for importing vector dat o o oa a 34 9 Polynomial degrees for georeferencing soosoo 0 202202 e eee 43 10 __A range of modules for exporting raster data o oaoa 44 11 __A range of modules for exporting vector data ooo 45 12 _ Operators iN r mapcalc o oo oa e a 99 13 Features IN r mapcalc aaoo a a we BOR 100 14 Internal variables in r mapcalc 2 a 101 15 GRASS digitization tools according to a e a Ee E ere amp 123 GDF Hannover Courses ix Preface Extensive support material is provided in the context of their tutorials by GDF Hannover bR 9 In this way the participant
19. add v category my3dmap_final op report An available attribute table can be assigned by the module v db connect GDF Hannover Courses 65 10 3 Managing vector attributes 10 3 Managing vector attributes Attribute management has completely changed in GRASS 6 0 The dig_cats structure in GRASS version 5 4 no longer exists All attributes are now saved in database tables and are linked with the geometries via a DBMI Database Management Interface The following DBMI drivers are presently available e DBF default e PostgreSQL database e MySQL database e via ODBC connected RDBMS e g Oracle MySQL PostgreSQL and so on The connection of a vectormap with an attribute table is GRASS internally defined in a dbln file This is an ASCII file which is saved in the vectormap folder The file is generated when a map is imported into GRASS If a table is supposed to be created later another link should be added to the file using the module v db connect The current connection of a map can be verified by the command v db connect p vector map The command v db connect makes the connection between a vectormap and an attribute table possible each table is thereby connected through different Layer entries v db connect map vectormap table attributel layer 2 v db connect map vectormap table attribute2 layer 3 v db connect p vectormap An example application is described in chapter 11 2 2 Note In this case i
20. analysis In this section we will intro duce some of the more frequently used raster GRASS modules The modules and the applications discussed here represent only a few of those currently available 9 3 1 Calculating transects In order to display a line transect in a raster diagram the menu driven module d profile can be used see Figure 16 d profile Raster cell values or aggregated values in case of median and arithmetic average along one or more transects can be listed in ASCII format using the module r profile It is possible to give coordinate pairs or interactively select start and endpoint option i The module r transect provides a front end to the r profile module It only needs the startpoint of the transect and calculates the endpoint automatically based on the parameters azimuth and distance r profile r transect 9 3 2 Line of sight analysis The r los module performs a line of sight analysis based on an elevation map A starting point the height above the ground at this point as well as the distance from this point up to which the line of sight analysis is to be calculated can be indicated via a coordinate As an example we will use the elevation map elevation 10m from the Spearfish data set The initial coordinate is specified in this case but can also be determined by the module d where Put the setting on relief model but 20m resolution g region rast elevation 10m res 20 pa Calculation of visibil
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22. basic operation types are available for creating thematic maps based on raster data 1 pointwise raster cell oriented or pixel oriented operation neighborhood operations 2 matrix oriented or pixel window supported operation moving window operations Besides using the ready to go GRASS modules which each provide a particular operation solution oriented operations of both types can be defined and applied via the arithmetic module r mapcalc see chapter 15 Raster data management The basic management for the components of raster data like the spatial reference of maps attribute and color assignment of the pixel is directly conducted by each raster modules when executed Thus the module r support used in former versions GRASS 5 0 and 5 3 is no longer necessary In addition the creation of map statistics with the module r support r is only calculated for the selected map cutout which in most cases was not intended and led to unintentional effects Help functions to the GRASS modules GDF Hannover Courses 49 9 1 Visualizing rastermaps A help file is available for nearly all of the more than 400 GRASS modules In this file the module is described and command syntax explained A short version of the help can be displayed by entering the module command with the parameter help at the prompt d rast help A detailed help with a module description and examples which is equivalent to the help pages on the GRASS homepage
23. better to use copyleft but if your program is non copylefted free software we can still use it 0 66 See Categories of Free Software for a description of how free software other categories of software relate to each other copylefted software and Sometimes government export control regulations and trade sanctions can constrain your freedom to distribute copies of programs internationally Software developers do not have the power to eliminate or override these restrictions but what they can and must do is refuse to impose them as conditions of use of the program In this way the restrictions will not affect activities and people outside the jurisdictions of these governments Most free software licenses are based on copyright and there are limits on what kinds of require ments can be imposed through copyright If a copyright based license respects freedom in the ways described above it is unlikely to have some other sort of problem that we never anticipated though this does happen occasionally However some free software licenses are based on contracts and contracts can impose a much larger range of possible restrictions That means there are many pos sible ways such a license could be unacceptably restrictive and non free We can t possibly list all the possible contract restrictions that would be unacceptable If a contract GDF Hannover Courses 129 based license restricts the user in an unusual way that copyrig
24. by window allows to zoom in the map by means of a window defined by the mouse Ac cordingly the assignment of the mouse buttons changes and is graphically displayed in parallel in the menu The mouse button allocation is identical to the module d zoom Zoom out with this button the user can automatically zoom out of the map in defined increments Pan allows the user to pan on the map The increment of the displacement is internally defined and can not be influenced Currently a connection between the pan module and the digitization module is still missing Also a rubber band function which allows the displacement during the digitization without interrupting the process is not yet available Zoom to default region sets the extent of the project to the default region g region d and re displays the maps Zoom to region sets the extent of the project to a former saved region A region can be saved via the command g region and the option save Redraw deletes the content of the monitor and redraws its content This function is necessary for instance when changing settings for the background map GDF Hannover Courses 77 11 6 Digitizing with GRASS Display categories makes it possible to display and also change category values and layer allo cation of individual features points lines boundaries and centroids by selecting them with the mouse Display attributes makes it possible to display and also change at
25. can be displayed by the command g manual module name For this purpose a standard browser is automatically opened and displays the corresponding help file g manual d rast amp 9 1 Visualizing rastermaps The visualization of raster data is conducted in a so called X monitor by the module d rast GRASS can manipulate up to 7 different monitors x0 x1 x2 x6 in parallel d mon x0 d rast Use the d zoom module to get a more detailed view of a regional cutout d zoom A particular cutout or the total work area can be defined via the module g region The setting of the default region with a resolution of 10 m can be achieved using g region d res 10 0 pa d erase d rast rastermap Note that the settings changed by g region must be passed to the monitor by the module d erase in order to be take effect It is also possible to adjust region and resolution settings directly from a raster map g region rast rastermap p d redraw Visual overlapping of two raster files d rast rastermap1 d rast o rastermap2 A pixel of the underlying rastermap1 is only visible if the corresponding pixel of the overlay rastermap2 contains a NULL values indicating a data gap The module d his also overlays maps e g for the visual verification of the georeferenced TK24 of the Spearfish sample dataset GDF Hannover Courses 50 9 2 Query of raster cell values and metadata d his n h_map roads i_map tk24 Visualization of a rastermap wi
26. com mands i e all file operations copy delete rename should be conducted with the appropriate GRASS commands g copy g remove g rename 2 3 1 The PERMANENT mapset All information about projection resolution and extent of the project area are stored within the com piled location in the PERMANENT mapset which is automatically generated by GRASS If necessary the core data original maps of the project can be stored here because only the user who created the new project has write permissions Due to the internal structure it is guaranteed that the data can not be changed by other users Other GRASS users and naturally the person who has write permissions for the PERMANENT mapset should create additional mapsets for creating saving and changing their own files and analysis results based on the core data in the PERMANENT mapset GDF Hannover Courses 6 2 3 The GRASS database Files in the PERMANENT mapset The access to a single mapsets can be controlled individually for each project Location in GRASS If no maps core data are saved in PERMANENT it will only contains files with information about the project area DEFAULT_WIND Specifications of the edge coordinates extension and resolution of the environment PERMANENT MYNAME Name of the project gt e g hanover PROJ_INFO Specifications of the projection gt e g tmerc Transverse Merca tor Projection bessel ellipsoid potsdam date PROJ_UNITS Specificati
27. created with Xfig can be found in figure 38 on page 115 The module d out png offers a simple variant for exporting a map displayed in the X monitor to the PNG format This module saves the screen content in a size selectable for a PNG file 17 3 Creating shading effects An interesting variant for displaying a shaded map can be done with the help of the expositions map aspect derived from an elevation model This can be achieved with the module d his d his h_map tk24 i_map aspect It is easily possible to provide an impression of a plastic surface by a clever combination of hue and GDF Hannover Courses 111 17 4 Processing maps with Xfig intensity see figure 35 F F Spearfish TK24 Spearfish aspect map in shaded relief map Figure 35 Creating simple shading effects with d his 17 4 Processing maps with Xfig The graphical programs Xfig 23 or Skencil 22 are often used for a nice design of analog maps These programs are available for creating professional layouts Different image formats such as TIFF PPM or PNG can be used for input The ourput format of the finished maps can be in Postscript Latex PDF and various other image formats The software packages Xfig and Skencil are Free Software like GRASS and can be installed from the Internet or from one of the known Linux distribution CD s The procedure of creating simple map layouts with Xfig is now supposed t
28. for GRASS 5 4 CVS cvs z3 co grassd1 for GRASS 6 0 CVS according to historical reasons 5 1 Subsequently this is compiled see Chapter 3 2 configure make make install Within the folder grass or grass51 an update of the source code can be downloaded with the following command in order to compile again make distclean Remove the already compiled parts of the source code cvs up dP Update the source code from the CVS GDF Hannover Courses 14 4 GRASS Project database In the GRASS database spatially oriented data are managed geocoded For this purpose a coordi nate system e g GauB Kriger UTM etc of the project region the so called Location needs to be decided upon before starting to work Consider the following As a rule it is indispensable to choose the structure and organization of the database to be used in GRASS and each GIS Extent of the project region All the data that are to be imported as part of a project must be contained within the spatial extent of the the Location In addition one must determine what projection is to be used for the project This is usually provided with the data to be used in the project and includes information about the projection such as projection name ellipsoid datum and other parameters Data resolution of raster data In general the computing and storage requirements increase exponentially with resolution However if the resolution is lower than that of
29. is a further new GUI concept On the one hand module depending pop up menus which open automatically when a module name without further parameters is entered in the GRASS Shell are part of this concept On the other hand GRASS has been supplemented by a new GIS manager This manager contains a range of ordinary functions which shall make the work with the mouse clearer and more comfortable see Figure 15 Furthermore all functions from TclTkGRASS 4 0 are integrated into the new GIS Manager co nit GRASS 6 0 cvs GIS Manager c i Bile GIS Display Raster Vector Image Grid3D Databases Help MO ewrias 727 98 OZ lnsue I F ASTER DEM AJ Einzugsgebiete Kliniken Osnabr ck B Gr nfl chen D Strassen F Einzugsgebiet Klinik 1 F Einzugsgebiet Klinik 2 Einzugsgebiet Klinik 3 D Einzugsgebiet Klinik 4 Einzugsgebiet Klinik 5 Einzugsgebiet Klinik 6 Einzugsgebiet Klinik 7 Line color B show lines Fill color D fill areas Random fill colors for each cat value _ GRASSRGB column for fill color Label color Label size le Label xpos left Label ypos center 4 Layer for labels Attribute col foriabeis Layer for query Category query SGL query W use query Query with mouse _ results as text in terminal W edit attributes form mode Display when avg region dimension is more thn oor less tina Figure 15 d m GIS Manager of GRASS 6 0 including FRIDA data
30. is necessary that these are integrated in the roadnet before An own category value is also assigned on which the later calculations are referred via the layer 2 This assignment is carried out by means of two operations Firstly the sites hospitals are extended with the line data roads to a new map roads_hospitals and the attribute tables are connected with each other via layer entries Intersection of the data v patch in roads hospitals out roads_hospitals GDF Hannover Courses 87 12 3 Assigning hospitals to the roadnet Control v info roads_hospitals gt dblinks 0 d erase Q vect roads_hospitals d vect roads_hospitals type point col red Define database if necessary db connect dr dbf database GISDBASE LOCATION_NAME MAPSET dbf Display attribute columns of the maps db describe c roads ncols 7 Column 1 cat Column 2 strShapeID Column 3 strID Column 4 strTypID Column 5 strSpuren Column 6 strEbene Column 7 strName gt The cat column has been added during the import via v in ogr Connect the attributes of the lines with the extended map v db connect roads_hospitals dr dbf data GISDBASE LOCATION_NAME MAPSET dbf table roads layer 1 key cat Connect the attributes of the points with the extended map v db connect roads_hospitals dr dbf data GISDBASE LOCATION_NAME MAPSET dbf table hospitals layer 2 key cat Control
31. is not included it is only part of GRASS 6 0 A binary version is based on the official source code of the GRASS Version 5 4 0 and has been precompiled on different computing and operating systems according to special guidelines Thus GRASS can be installed on your computer without additional compiling in most cases This needs a compatible binary version for your system available and further necessary libraries are installed for interacting with GRASS In this place we want to illustrate the installation of a binary version A binary version of GRASS 5 4 0 is presently available for GNU Linux systems This version has also been precompiled on a GNU Linux system according to defined criteria The descriptions of the system and used parameter for precompiling can be found in the appropriate download area Therefor the program and the appropriate installation script need to be downloaded into an arbitrary directory before installing the version with root permissions su RK sh grass5 4 0_i686 pc linux gnu_install sh grass5 4 0_1686 pc linux gnu_bin tar gz If the requirements differ from these requirements it is necessary to compile the present source code of the version GRASS 5 4 0 on your own computer This procedure can be useful because the binary version mostly does not include all features and modules e g external database support The GRASS 5 4 0 source code and the related binaries can be downloaded directly from the Internet page
32. line tracing the shortest distance between two geographic points along a great circle in a longitude latitude data set Program for generating and displaying simple graphics to the graphics display monitor Overlays a user specified grid in the active display frame on the graphics monitor Displays the result obtained by combining hue intensity and sat uration his values from user specified input raster map layers Displays a histogram in the form of a pie or bar chart for a user specified raster file Display information about the active display monitor Displays a legend for a raster map layer in the active frame on the graphics monitor Prosecution on next side GDF Hannover Courses 139 Prosecution Command description d linegraph Generates and displays simple line graphs in the active graphics monitor display frame d m d mapgraph Generates and displays simple graphics on map layers drawn in the active graphics monitor display frame d measure Measures the lengths and areas of features drawn by the user in the active display frame on the graphics monitor d mon To establish and control use of a graphics display monitor d monsize Selects starts specified monitor at specified size d nviz Create fly through script to run in NVIZ d out png Saves active display monitor to PNG file in home directory d paint labels Displays text labels formatted for use with GRASS paint p labels p map output to the acti
33. makes possible to save maps in different image formats The current possible formats are Postscript PDF and PNG The map is saved in the current extent and resolution GDF Hannover Courses 48 9 Working with raster data From simple queries to complicated algebraic functions and logical conditions practically any analysis and modeling are possible with raster data in GRASS GIS Due to the large number of raster data analysis modules currently available more than 100 this chapter will provide a general intoduction to raster data processing The topic of remote sensing which means the processing and analysis of satellite and aerial images is not part of this book and plays a subordinated role Some literature concerning remote sensing analysis is specified in the bibliography As described in chapter 8 most of the analyses can be executed using the graphical user interfaces TcITKGRASS and GIS Manager Here we will explain each step of the anaysis as a GUI operation as well as a command line instruction The use of GRASS at the command line prompt is highly rec ommended in order to familiarize the user with individual modules their usage and the parameters they require General information concerning raster data A raster value is defined by its localization coordinates x y cell center and a z value which cor responds to a measurement or object value which is usually assigned a color or grey value when displayed Two
34. oD 1D 2D 2 5D Figure 4 Data dimensions in GIS 2 3 The GRASS database Geodata are internally saved by GRASS in a standard subdirectory called a GRASS database In most cases a new folder e g grassdata is created in the users s Home directory before GRASS is installed for the first time cd Linux changes automatically to the Home directory of the user mkdir grassdata Compiling the subdirectory for the GRASS database A subdirectory tree Location will automatically be created in GRASS for each project region defined in GRASS All project data are saved in the Location subdirectory The Location can be further subdivided into map subdirectories called mapsets This is how GRASS controls the organization and the access to the data see chapter 2 3 1 and 2 3 2 GDF Hannover Courses 5 2 3 The GRASS database GRASS Database Location Mapset Geometry and attribute data prov_bz meran huber r cellhd _cell_mise europa cor home user grassdata 3 hannover kronsberg feel world europe vector Figure 5 Example structure of a GRASS 6 0 database Since different components geometry attribute and graphics data of the individual layers are stored in different subdirectories all management of the project data should be done using GRASS
35. of this License and multiple identical Invariant Sec tions may be replaced with a single copy If there are multiple Invariant Sections with the same name but different contents make the title of each such section unique by adding at the end of it in paren theses the name of the original author or publisher of that section if known or else a unique number Make the same adjustment to the section titles in the list of Invariant Sections in the license notice of the combined work In the combination you must combine any sections Entitled History in the various original docu ments forming one section Entitled History likewise combine any sections Entitled Acknowledge ments and any sections Entitled Dedications You must delete all sections Entitled Endorse ments COLLECTIONS OF DOCUMENTS You may make a collection consisting of the Document and other documents released under this License and replace the individual copies of this License in the various documents with a single copy that is included in the collection provided that you follow the rules of this License for verbatim copying of each of the documents in all other respects You may extract a single document from such a collection and distribute it individually under this License provided you insert a copy of this License into the extracted document and follow this License in all other respects regarding verbatim copying of that document AGGREGA
36. out bin Binary Array r out gridatb GRIDATB FOR TOPMODEL r out gdal Over 20 important formats are supported see paragraph Export with GDAL Note The Arc Toolbox in ArcGIS supports the import of ASCll grids Import to Raster gt ASCII to Grid The result can be selected in ArcCatalog Be aware that the extension Spatial Analyst must be present and activated As mentioned in chapter 5 1 for exporting raster data the special characteristic of GRASS has to be considered that raster maps are always exported with the current resolution and only for the just determined region current region Thus it is always advisable to ascertain in the forfront with the command g region p if the present settings of the region are correct before exporting importing and analyzing raster data GDF Hannover Courses 44 7 2 Exporting vector data Export with GDAL The module r out gdal is able to export GRASS raster data into different formats An appropriate list can be displayed with the command r out gdal 1 In order to use this module it is presently necessary to install GDAL with GRASS Support For this purpose the ready to install binary packages need to be installed If no binary package is available for your platform it needs to be built from source Please obtain detailed information about this topic from GDF Hannover bR 7 2 Exporting vector data In table 11 the available modules in GRASS are listed
37. patUTM PERMANENT pcbs qbird a sard_xy shizuoka slovakia57 song_fusion SpearfishLL SpearfishNAD83 SSS Py Ps wif Enter GRASS Create New Location Create Location From EPSG Help Exit Figure 7 TclTk start screen in GRASS Here an existing Location and mapset can be chosen from the menu or a new Location and mapset can be created If a new mapset is to be added to an existing Location first choose the appropriate Location then enter the name of the new mapset in the window below the text Create New mapset and click the button Create see Fig 7 There are three ways to create a new Location A The projection data can be provided directly by the user The necessary information can usually be found in the metadata associated with the data file B The projection can be assigned automatically by entering the appropriate EPSG code see http www epsg org This assigns standard projection and national grid systems parameters to the Location The appropriate code number can be found in the menu see Fig 9 or as metadata C The projection data can be imported directly with the data by using the importmodules r in gdal and v in ogr A In order to define the projection of a Location itself click with the mouse on the button Create New Location GRASS changes to the text based mode which can also be your start screen depending on the start settings see Fig 8 The data
38. r sum r sun r sunmask r surf area r surf contour r surf fractal Makes each ouiput cell value a function of the values assigned to the corresponding cells in the input raster map layers Creates shaded relief map from an elevation map DEM Generates raster map layers of slope aspect curvatures and par tial derivatives from a raster map layer of true elevation values Aspect is calculated counterclockwise from east Simulates elliptically anisotropic spread on a graphics window and generates a raster map of the cumulative time of spread given raster maps containing the rates of spread ROS the ROS directions and the spread origins It optionally produces raster maps to contain backlink UTM coordinates for tracing spread paths Recursively traces the least cost path backwards to cells from which the cumulative cost was determined Category or object oriented statistics Generates area statistics for raster map layers Sums up the raster cell values Computes direct beam diffuse and reflected solar irradiation raster maps for given day latitude surface and atmospheric con ditions Solar parameters e g sunrise Sunset times declination extraterrestrial irradiance daylight length are saved in a local text file Alternatively a local time can be specified to compute solar incidence angle and or irradiance raster maps The shadowing effect of the topography is optionally incorporated Calculates cast shadow areas from
39. routine produces the quantization file for a floating point map Generates random cell values with spatial dependence Creates a raster map layer and vector point map containing ran domly located sites Generates random surface s with spatial dependence Reclasses a raster map greater or less than user specified area size in hectares Creates a new map layer whose category values are based upon the user s reclassification of categories in an existing raster map layer Recode raster maps Sets the boundary definitions for a raster map Calculates linear regression from two raster maps y a b x Reports statistics for raster map layers Reinterpolates and computes topographic analysis from input raster file to a new raster file possibly with different resolution using regularized spline with tension and smoothing GRASS raster map layer data resampling capability Rescales histogram equalized the range of categoryvalues in a raster map layer Rescales the range of category values in a raster map layer Generates three or four raster map layers showing 1 the base perpendicular rate of soread ROS 2 the maximum forward ROS 3 the direction of the maximum ROS and optionally 4 the maximum potential spotting distance Prosecution on next side GDF Hannover Courses 148 Command Prosecution description r series r shaded relief r slope aspect r spread r spreadpath r statistics r stats
40. the Free Software Foundation Europe 10 Status July 2005 Copyright 2004 2005 GDF Hannover bR Editors Otto Dassau Stephan Holl Markus Neteler Dr Manfred Redslob Translated by Kerstin Holl Internet http www gdf hannover de Contact info gdf hannover de Permission is granted to copy distribute and or modify this document under the terms of the GNU Free Documentation License Version 1 1 or any later version published by the Free Software Foun dation with no Invariant Sections A copy of the license is included in the section entitled GNU Free Documentation License Contents Contents List of figures vii List of tables ix Preface x 1 Introduction 1 2 Design and Structure 2 2 1 Geographical Data Stee ed tek Oe ee ea ae N e een dk kee a a eee 2 2 2 Data dimensions in GIS ane a eee eee a eee Ae eh eee SS 4 2 3 The GRASS database 2 a 5 2 0 1 The PERMANENT mapsel 2 4 48 3856 e484 bee te Ew teens 6 2 3 2 Design of furthermapsets 2 200 eee eee 7 2 4 Command structureinGRASS 0 0 00 ee 8 2 5 Hel
41. the orientation or decimal system pos neg degree with decimal places 4 4 2 2 and 3 dimensional coordinate systems In order to specify sites numerically on a map projection rectangular cartesian coordinates are used where the positive y values are pointed to the East and the positive x values are pointed to the North The zero point is differently defined in each system in GRASS usually in the left edge below In contrast to geographical and geocentric coordinates sites are only available for one defined illustration range e g meridian stripes Numerous coordinate systems are applied internationally Besides different zero points and dimension units different ellipsoids and projections are chosen as basis This results in the fact that a transformation is mostly only possible via a complex calculating operation In GRASS several modules are available for this purpose r proj and v proj Now we briefly want to introduce theoretical examples of the GauB Kriiger and UTM coordinate systems which are used in Germany Gau Kr ger coordinate system This meridian stripe system has been established in Germany in 1927 The Bessel ellipsoid is the chosen land survey datum the transverse mercator projection is the projection and potsdam is the datum The coordinates refer to one meridian stripe each whereas the longitudes 6 9 12 and 15 as main meridians x axis are valid in Germany The distortion can be reduced to a maximum o
42. v in ogr SHAPE file UK NTF SDTS TIGER S57 MapInfo File DGN VRT AVCBin REC Memory GML ODBC see also http www gdal org ogr ogr_formats html v in ascii GRASS ASCII v in e00 Arclinfo E00 format v in db Create vectors from database with x y z coordinates Importing a SHAPE File The module for importing SHAPE data to GRASS is called v in ogr Note that the SHAPE format is not a topological format there are no situation and or neighbor relations between the individual objects For example border lines between two areas polygones are saved twice This may lead to problems and therefore has to be corrected by GRASS during the import process The data for this exercise comes from the FRIDA project 17 which maintains a large quantity of GDF Hannover Courses 34 5 3 Importing sites detailed vector data of the city of Osnabrueck which are made available by Intevation GmbH 13 v in ogr o dsn frida 1 1 shp joined streets joined shp out streets 12323 primitives registered O areas built O isles built Number of nodes 8937 Number of primitives 12323 Number of points 0 Number of lines 12323 Number of boundaries 0 Number of centroids 0 Number of areas 0 Number of isles 0 Within GRASS under GISDBASE LOCATION MAPSET a subfolder named streets has been created in the directory vector during the import In this directory the topology to
43. vector map v in ogr Convert OGR vectors to GRASS Available drivers v in region Create a new vector from current region v in sites all v in sites Converts a GRASS site _lists file into a vector file v info Outputs basic information about a user specified vector map layer v kcv Randomly partition points into test train sets v kernel Generates a raster density map from vector points data using a moving 2D isotropic Gaussian kernel or optionally generates a vector density map on vector network with a 1D kernel v label Create paint labels for GRASS vector file and attached attributes v mkgrid Creates a binary GRASS vector map of a user defined grid v neighbors Makes each cell value a function of the attribute values assigned to the vector points or centroids around it and stores new cell values in an output raster map layer v net alloc Allocate subnets for nearest centres direction from centre Cen tre node must be opened costs gt 0 Costs of centre node are used in calculation v net Network maintenance v net iso Split net to bands between cost isolines direction from centre Centre node must be opened costs gt 0 Costs of centre node are used in calculation v net path Find shortest path on vector network Reads start end pointsfrom v net salesman v net steiner v normal v out ascii standard input in 2 possible formats Create a cycle connecting given nodes Traveling salesman prob lem Note that T
44. vectorization r thin in raster out raster_thin r to vect in raster_thin out raster_vect feature line GDF Hannover Courses 92 13 1 Vectorization of raster data Figure 28 Smoothing vectorized data If vector contour lines are supposed to be created from an available relief model x y z this can be carried out by the module r contour In this case isolines are calculated and vectorized under indication of a certain increment distance step The reasonable increment to be chosen depends on the slope and the map scale Vectorization into areas For vectorizing raster areas the module r to vect including the parameter feature area is to be used r to vect in raster_thin out raster_vect feature area Smoothing vectorized lines and area data A newel according to the chosen pixel resolution does generally occur during the conversion of raster data into vector data Thus GRASS offers the possibility to smooth this under indication of an accu rately threshold to be chosen via the module v clean and the parameter prune Resulting steps depending on the set resolution can be visible in the resulting map This occurs because the converting modules do not follow the raster pixel center during the vectorization but conduct the line creation via the pixel borders GDF Hannover Courses 93 13 2 Converting vector data into the raster model In figure 28 the smoothing of a vectorized raster line is s
45. which are able to export GRASS vector data into different external vector formats Table 11 A range of modules for exporting vector data GRASS Export Module commands Vector formats v out ascli GRASS ASCII v out ogr SHAPE TIGER S57 MapInfo DGN Memory CSV GML ODBC and PostgreSQL v out pov Povray 7 3 Exporting sites In GRASS 6 0 sites are considered as vectors The known sites formats from GRASS 5 4 can still be exported via the module s out ascii Otherwise the module v in sites is used in order to convert existing sites data into the vector format and then to transform them into different export formats Exporting elevation data from raster maps For exporting elevation data from a raster map into the xyz format it is necessary to adjust the res olution of the location to the resolution of the raster map Afterwards the X Y and Z values will be written into an ASCII file cell by cell g region rast elevation dem p r stats 1 g input elevation dem gt spearfish_elevation txt GDF Hannover Courses 45 8 Graphical user interface In the field of GIS usability plays a more and more important role Although GIS traditionally preferred the prompt From this point of view we want to go into the development of the graphical user interface of GRASS GIS because a lot of innovations and updates have taken place in the last month and years 8 1 GIS Manager Since GRASS 6 0 there
46. x base b F max x y Z largest value of those listed median x y z median value of those listed min x y z smallest value of those listed mode x y z mode value of those listed not x 1 if x is zero 0 otherwise rand a b random value between a and b round x round x to nearest integer Ic sin x sine of x x is in degrees F sqrt x square root of x F tan x tangent of x x is in degrees F The result is a floating point value if a constant is a floating point value gt The result is a floating point value The result is an Integer value GDF Hannover Courses 100 15 3 Internal variables in r mapcalc 15 3 Internal variables in r mapcalc Table 14 Internal variables in r mapcalc Variable Meaning row current row of moving window col current col of moving window x current x coordinate of moving window y current y coordinate of moving window ewres current east west resolution nsres current north south resolution null NULL value For explaining the different interpretation of r mapcalc instructions two simple examples are follow ing Raster map soils minus map reclass multiplied by 2 New map soils reclass 2 Raster map soils reclass multiplied with 2 New map soils reclass 2 15 4 Masking The masking of image ranges can preliminarily be helpful for image analysis It is possible to use an alr
47. 0 9 7 Digitizing raster data Example using the Spearfish dataset You have a landuse map landuse and you only want to analyse this map in areas where the ground height lies above 1200 m In order to determine this limit choose the elevation map elevation 10m which you are able to convert into a mask via the module r mapcalc The creation of the mask could be as follows g region rast elevation 10m p r mapcalc mask1200 if elevation 10m gt 1200 0 1 nu11 g copy rast mask1200 MASK Only raster data are analyzed in those ranges for which a 1 is indicated in the MASK map as long as the map MASK is available in the current mapset This should be verified by displaying the map d rast elevation 10m d rast o roads During any project the availability of a mask in the command line can be recognized by the reap pearing text Raster MASK present For deleting the MASK the command g remove is used Afterwards the total current region is involved in the analysis again g remove rast MASK If the created mask is supposed to be used again later it can also be renamed in order to deactivate it g rename rast MASK Mask 9 7 Digitizing raster data GRASS offers the possibility to digitize points lines and areas based on raster via the module r digit Thereby each feature can be assigned with a category value and a label r digit Please choose one of the following A define an area C define a circle L define a
48. 01 7 cat coords3d txt v in ascii z out elevation v category in elevation out elevation2 op add v category elevation2 op report Examples of how to extract sites from existing databases are given in chapter 10 GDF Hannover Courses 37 6 Georeferencing This chapter can be skipped if no unreferenced data are to be imported In order to import scanned raster maps to be later georeferenced two project regions need to be defined The scanned maps are first imported in a XY location without projection and afterwards equalized geocoded in a second location with a defined coordinate system GRASS target location with geocoding GRASS XY Location without geocoding scaned raw map rectified result map Figure 13 Implementation of georeferencing in GRASS 6 1 Preparation for georeferencing The desired projection of the target location is to be defined before starting the equalization according to the required geographical borders and resolution In principle any projection supported by GRASS can be defined The resolution of the target location should not be too low If the resolution of the target location is too low compared to the resolution of the data to be georeferenced resampling during the georeferencing process will result in a low quality digital map data loss On the other hand too high relative resolution will result in a high quality map requiring an unreasonable amount of stora
49. 1 Shapelib Software Suite http shapelib maptools org 2004 22 Skencil http www skencil org 2004 23 Xfig Software Suite http www xfig org 2004 GDF Hannover Courses 156
50. 15 Raster map arithmetic with r mapcalc 99 15 1 Operators in r mapcalc 2 ee ee ae oS ode Ge wee He ee Oe 99 15 2 Features in r mapcalc 2 2 eae 6 eA ee ER RSS EEE EE Ode oe BS 100 15 3 Internal variables in r mapcalc 2 1262446 a eee wow Pe ee Gee ee eee 101 15 4 Masking ode eee de aee te heaee Giga vee ehadieteoaeecdgaees 101 16 3D visualization and animation 103 16 1 Displaying a 3D map with NVIZ 2 et 103 16 2 Displaying raster volume layers VOXEL Ethos ae cae ae eee ee a ee ee 105 16 3 Creating an animation 2 22 2 e028 heave eebeteettavevebadees 107 17 Visualizing and creating maps ready for press 108 17 1 Map export into a postscript map 22 46 eee ee ee ee 108 17 2 Map export with PNG driven s t44s5e2 62528 bea dee obatade es 111 17 3 Creating shading effects 2 2 ee 111 17 4 Processing maps with Xfig Aa a a G Gye a a G aks e as 112 17 5 Processing maps with Skencil aooaa a 116 18 QGIS 117 18 1 Working with vector and raster data o oo e 0 002000 02 eee 117 18 2 Visualizing and categorizing Be ery ea ee Bee Boe ara etch ee Oe a A 120 18 3 Editing op a oh aoe ne Sak gs ee Gea Ene ee eee ae Soe a ete ee ee 121 18 3 1 GRASS vectordata ss sce amp ca ace ee RA atk a a eh a ae eB 122 18 3 2 Shapefile lt 2 sco eo5 56d 2 oem SEP eSeEe ae O54 oR A SS eR EES 123 18 4 GRASS ToolDOX 2254 62 46 55504646993 2 44 84g BG edb es 2h A 124 18 5 Processing GPS data 60 be Ra ee Bk Oe he oe oR a E
51. 23 BOOSO8Se0R8E8 Qaaa4soeagase iT PE pepe fees ft fan a LiL Gegkseseeaa22 BRE OUBEEBOBREREB ik g F 3 fa eaeaaacade geese melt letclelet l 1 1 Figure 34 Simple result map ps map Soil map with legend in the Spearfish region 110 GDF Hannover Courses 17 2 Map export with PNG driver 17 2 Map export with PNG driver In the GRASS monitor maps are displayed with screen resolution The PNG driver offers the possibility to display images in a higher resolution and guarantees TRUE COLOR 24 bit quality The application of the PNG driver is almost identical to the usage of the GRASS monitor The creation of a TRUE COLOR image of the soils map with overlaying roadnet from the Spearfish example dataset is carried out as follows d mon start PNG d mon select PNG The maps are called up d rast soils d vect roads col black the PNG driver is terminated and the GRASS monitor used before is chosen again d mon stop PNG d mon select x0 A map map png occurs in the current directory that can be viewed with a graphical program such as xv The exact settings of the resolution of the PNG map can be defined before with the following variables export GRASS_WIDTH lt width gt export GRASS_HEIGHT lt height gt export GRASS_PNGFILE lt name of the resulting file gt export GRASS_TRUECOLOR TRUE FALSE The result can now be processed in graphical programs such as Xfig or Skencil A simple map layout
52. 28 13 Implementation of georeferencinginGRASS 20200 4 38 14 Searching control points of a scanned topographical map with the GRASS module points a o s dow ewe Ge ee GO ee a oe Sek eae Ge eo ee 41 15 d m GIS Manager of GRASS 6 0 including FRIDAdata 46 16 Representation of different line transects of a relief model with d profile 54 17 _Buffering raster data with r buffer 2 2 2 ee ee 56 18 Representation of the GRASS 6 0 vector architecture 63 19 VMAPO data Germany oaaao noona aa 73 20 Digitizing GUI of the module v digitl a saoao oaaao aoso 76 21 _Topographical map of the Spearfish region including landuse information 79 22 Creating an attribute table during digitization o o sosoo a 80 23 Attribute entry during TE m a R a ceo a a Oe a en es 82 24 Settings of the snapping threshold during digitization 84 25 Basemap Roads and hospitals of Osnabrueck aaoo 86 26 __ Assignment of the next achievable roads to the hospitals 90 27 Modules for converting raster data into vectordata 92 28 Smoothing vectorized data 6 6s 6 a A ER eR HES 93 29 Modules for converting vector dataintorasterdata 94 30 _NVIZ graphical control window ns eee eS ee Eee Ee 103 31 Volume panel for volume layer visualization 2 00000040 105 32___ Different precipitation
53. 41 Command Description g access g ask Prompts the user for the names of GRASS data base files g copy Copies available data files in the user s current mapset search path and location to the appropriate element directories under the user s current mapset Prosecution on next side GDF Hannover Courses 142 Prosecution Command description g filename Prints GRASS data base file names g findfile Searches for GRASS data base files and sets variables for the shell g gisenv Outputs the user s current GRASS variable settings g list Lists available GRASS data base files of the user specified data type to standard output g manual display the HTML man pages of GRASS g mapset Change current mapset g mapsets Modifies the user s current mapset search path affecting the user s access to data existing under the other GRASS mapsets in the current location g mlist Apply regular expressions and wildcards to g list g mremove Apply regular expressions and wildcards to g remove g parser g parser g proj Prints and manipulates GRASS projection information files g region Program to manage the boundary definitions for the geographic region g remove Removes data base element files from the user s current mapset g rename To rename data base element files in the user s current mapset g setproj g setproj g tempfile Creates a temporary file and prints the file name g version Displays version and copyrig
54. 4s ea Be ee A eR A E 74 14 2A DataOVSIAY 26 4 4c Sa dda dd hOGA SA RAS GRDA REARS ADE EDS 74 11 3 Data extraction 2 202 0020 2 ee 74 11 4 Data selection s soo cota 20 202 ee 75 11 5 Topology managemen t aaoo a eS eS ee ee wee eee 75 11 6 Digitizing with GRASS aoaaa a 76 12 Application example vector based optimization of operation areas 85 12 1 Importing example data ee saoo Ee ERK RR eR ee we eS 85 12 2 Extracting hospitals from the point file lt lt se 62s eke hee eGR eee eS 87 12 3 Assigning hospitals to the roadnet i he he eS SSS ES SE a She ee owe S 87 12 4 Assignment of the regions of optimal achievability p gasin io to Den e ao eh a 89 13 Data conversion 92 13 1 Vectorization of raster data ee as ek ee SESE eS SEU Kee ES 92 13 2 Converting vector data into the raster model a no aoao 94 14 Data interpolations 96 14 1 Data interpolation into the raster model aooaa 0000020004 96 14 1 1 Inverse Distance Weighted a aaao 00200 ee eee 96 14 1 2 Regular splines with tension interpolation oaoa aa 97 14 2 Data interpolation into the vector format a aoao 00000 00048 97 GDF Hannover Courses v Contents
55. ASS 5 0 5 4 v in shape d in vector_areas shp Attribute layers available in vector_areas shp 1 ShapeID int4 4 2 TypID int4 2 3 Name text 50 4 TypName text 50 lt q in shape in vector_areas shp out vector attr TypID label TypName 11 1 Network analysis In general network analyses are based on vector topology Various network analysis modules are available because GRASS is a topological GIS which has been supplemented by DGLib Directed Graph Library GDF Hannover Courses 70 11 1 Network analysis e Shortest Path Analysis d path and v net path e Subnets within a vector network v net alloc e Minimum Steiner Tree Problem v net steiner e Travelling Salesman Problem v net salesman e Cost analysis v net iso As an example the optimization of hospital catchment areas is explained in chapter 12 11 1 1 Shortest Path Analysis The shortest distance between two given points can be determined in two different ways By default the length of the vectors is used as cost source Other attributes of the vectors like information about the speed limit on the road or information about the road status can be used for calculating a path Cost information can also be assigned to both vector directions Attributes of the nodes e g cycle times of the traffic lights at a crossroad can also be considered d path d path directly calculates the shortest distance between two given points on the GRASS monit
56. An introduction to the practical use of the Free Geographical Information System GRASS 6 0 Version 1 2 2004 2005 GDF Hannover bR Imprint This document is no original documentation of the described software The software and hardware descriptions named in this document are in most cases registered trademarks and are therefore subject to the legal requirements GRASS GIS is subject to the GNU General Public License Find more information on the GRASS GIS Homepage 12 The details data results etc that are given in this document have been written and verified to the best of knowledge and responsibility of the editors Nevertheless mistakes concerning the content are possible Therefore all data are not liable to any duties or guarantees The editors and publishers do not take any responsibility or liability for failures and their consequences Your are always welcome for indicating possible mistakes This document has been set with IATEX It is available as ATEXsource code online as HTML as well as in printed version via the GDF Hannover bR 9 The figures shown in this script are based on Free Geodata The figures and the used software are either liable to the Public Domain the GNU General Public License or an appropriate license Further information concerning Free Software GRASS GIS and Free Geodata can be found on the Internet pages of the GRASS User Association e V GAV 14 of the FreeGIS Project 16 and
57. DBMS If data with coordinate pairs X Y and attributes are available as DBF CSV MS Excel PostgreSQL and so on it is possible to generate a map in GRASS A simple table stations saved in PostgreSQL in the database mydb is used for this example v in db driver pg database host localhost dbname mydb user postgres table stations x east y north z quota key ID output stations If no ID column is available in dBase tables you need to create an incremental ID number using an external programs e g Openoffice org GDF Hannover Courses 64 10 2 Management of vector geometries 10 2 3 Creating geometries using XY and or XYZ textfile If XY or XYZ coordinates are saved as a simple ASCII text coords txt 2D or 3D maps can be created as follows a Example for a 2D map 1664619 5103481 1664473 5095782 1664273 5101919 1663427 5105234 1663709 5102614 Import to GRASS cat coords txt v in ascii out my2dmap Supplementation of missing category values for attaching attributes later v category in my2dmap out my2dmap_final op add v category my2dmap_final op report b Example for a 3D map 1664619 51034811445 1664473 50957821534 1664273 51019191532 1663427 5105234 454 1663709 5102614 525 N PON EF Import to GRASS cat coords txt v in ascii z out my3dmap Supplementation of missing category values for attaching attributes later v category in my3dmap out my3dmap_final op
58. GRASS Toolbox Since QGIS version 0 7 the GRASS plugin GRASS Tools includes GRASS functionality It allows to run GRASS modules from QGIS if it was started from a GRASS shell The modules work with GRASS data only It is easy to modify the menu and add new modules e E E aa Modules S 0 Vector overlay 0 pVector union 5 0 fi Vector intersection D 0 P Vector subtraction i L 0 Vector non intersection Buffer i ie Yp vector buffer ba g Raster buffer Extract features from vector i i D Select features overlapped by features in another map phe 4 E Select features by attributes Geomorphology i B cenerate slope map from DEM digital elevation model i Jsenerate aspect map from DEM digital elevation model Convert a vector to raster i ra E Convert a vector to raster using constant Convert a raster to vector Figure 47 QGIS Toolbox GDF Hannover Courses 124 18 5 Processing GPS data The toolbox provides an XML interface for easy implementation of more GRASS commands Cur rently there are modules like vector analysis v overlay v select v extract and raster analysis r slope aspect is implemented It is possible to include further GRASS modules if they provide a command line interface and can be controlled with parameters Programming skills are not necessary to implement GRASS modules so that adaptions to the per sonal needs are easy Further informa
59. License or any later version applies to it you have the option of following the terms and conditions either of that specified version or of any later version that has been published not as a draft by the Free Software Foundation If the Document does not specify GDF Hannover Courses 137 a version number of this License you may choose any version ever published not as a draft by the Free Software Foundation ADDENDUM How to use this License for your documents To use this License in a document you have written include a copy of the License in the document and put the following copyright and license notices just after the title page Copyright YEAR YOUR NAME Permission is granted to copy distribute and or modify this document under the terms of the GNU Free Documentation License Version 1 2 or any later version published by the Free Software Foundation with no Invariant Sections no Front Cover Texts and no Back Cover Texts A copy of the license is included in the section entitled GNU Free Documentation License If you have Invariant Sections Front Cover Texts and Back Cover Texts replace the with Texts line with this with the Invariant Sections being LIST THEIR TITLES with the Front Cover Texts being LIST and with the Back Cover Texts being LIST If you have Invariant Sections without Cover Texts or some other combination of the three merge those two alternatives to suit the situation If
60. OTAL 1519 00000 A display of univariate statistics values is possible via the module r univar This calculates the number of pixels and the minimum maximum arithmetical average median variance standard de viation and variance coefficient of the map attribute based on the current region and raster resolution settings g region rast elevation 10m p r univar g elevation 10m n 2654802 min 1061 06 max 1846 74 range 785 679 mean 1348 37 stddev 175 494 variance 30798 3 coeff_var 13 0153 9 6 Methods for manipulating rastermaps 9 6 1 Reclassification When classifying a rastermap a new attribute table for the rastermap is created The actual map remains unaffected The memory requirement is small because this only involves a table The source map is however the necessary base map for the new classified map The module r reclass can be operated interactively or via the command line prompt The necessary classification standards should be saved in a file which is indicated at the time of execution of the module The exact command syntax should be looked up in the detailed description g manual r reclass before using it AS an example assume the roadmap roads in the Spearfish region needs to be reclassified Instead of the five available categories only a specification of good or bad condition is needed CLASSIFICATION BEFORE r report roads 1 interstate 2 primary highway hard surface 3 secondary highway hard
61. PSET g gisenv MAPSET To modify a variable use the following syntax g gisenv set OVERWRITE 1 This will set the variable OVERWRITE to overwrite mode which is deactivated by default A detailed list of GRASS specific variables can be found at the help pages g manual variables Note Besides the currently mentioned variable OVERWRITE it is also possible to force the vector and rastermodules to overwrite maps by using the switches o or overwrite with two minus signs So it it possible to force overwriting during each command individually but default maps are still write protected GDF Hannover Courses 10 3 Installation of GRASS Three different variants can be chosen when deciding to install GRASS GIS on your computer Al though this book is an introduction into GRASS version 6 0 installation of the version 5 4 will be discussed briefly The choice of which version to install depends on the requirements of the user and the applications that are necessary for the project work with GRASS GIS The GRASS versions can be described as follows e GRASS 5 4 This version finishes the development of the official GRASS 5 x series It is used for production work in companies for many years now It can surely be considered as a very robust and stable version GRASS 5 4 covers all raster functionality of GRASS 6 0 0 but not the new vector functionalities For users who only need raster functionalities GRASS 5 4 is a save c
62. RASS r info Outputs basic information about a user specified raster map layer Prosecution on next side GDF Hannover Courses 146 Prosecution Command description r kappa Calculate error matrix and kappa parameter for accuracy assess ment of classification result r le patch r le pixel r le setup t le setup r le trace r los Line of sight raster analysis program r mapcalc rmapcalc r mapcalculator r mapcalculator Calculates new raster map from r mapcalc ex pression r median r mfilter r mode r neighbors r null r out arc r out ascii r out bin r out gdal r out gridatb r out mat r out mpeg r out png r out pov r out ppm r out ppm3 r out tiff Finds the median of values in a cover map within areas assigned the same category value in a user specified base map Raster file matrix filter Finds the mode of values in a cover map within areas assigned the same category value in a user specified base map Makes each cell category value a function of the category values assigned to the cells around it and stores new cell values in an output raster map layer The function of r null is to explicitly create the NULL value bitmap file Converts a raster map layer into an ESRI ARCGRID file Converts a raster map layer into an ASCII text file Exports a GRASS raster to a binary array Exports GRASS raster data into various formats requires GDAL Exports GRASS raster map to GRIDATB FOR m
63. SP is NP hard heuristic algorithm is used by this module and created cycle may be sub optimal Create Steiner tree for the network and given terminals Note that Minimum Steiner Tree problem is NP hard and heuristic algo rithm is used in this module so the the result may be sub optimal tests for normality for points Convert a GRASS binary vector map to a GRASS ASCII vector map Prosecution on next side GDF Hannover Courses 152 Prosecution Command description v out dxf Exports GRASS vector files to DXF file format v out ogr Convert to OGR format v out pov Convert to POV Ray format GRASS x y z gt POV Ray x z y v overlay Overlay 2 vector maps v patch Creates a new binary vector map layer by combining other binary vector map layers v perturb Random location perturbations of GRASS sites v proj Allows projection conversion of vector files v qcount indices for quadrat counts of sites lists v random Randomly generate a GRASS vector points map v reclass Changes vector category values for an existing vector map ac cording to results of SQL queries or a value in attribute table col umn v sample Sample a raster file at site locations v segment Create points segments from input lines and positions read from stdin in format v select Select features from ainput by features from binput v surf idw Surface interpolation from sites data by Inverse Distance Squared Weighting v surf rst Interpolatio
64. TION WITH INDEPENDENT WORKS A compilation of the Document or its derivatives with other separate and independent documents or works in or on a volume of a storage or distribution medium is called an aggregate if the copyright resulting from the compilation is not used to limit the legal rights of the compilation s users beyond what the individual works permit When the Document is included in an aggregate this License does not apply to the other works in the aggregate which are not themselves derivative works of the Document If the Cover Text requirement of section 20 is applicable to these copies of the Document then if the GDF Hannover Courses 136 Document is less than one half of the entire aggregate the Document s Cover Texts may be placed on covers that bracket the Document within the aggregate or the electronic equivalent of covers if the Document is in electronic form Otherwise they must appear on printed covers that bracket the whole aggregate TRANSLATION Translation is considered a kind of modification so you may distribute translations of the Document under the terms of section 20 Replacing Invariant Sections with translations requires special permis sion from their copyright holders but you may include translations of some or all Invariant Sections in addition to the original versions of these Invariant Sections You may include a translation of this License and all the license notices in the
65. al query at the monitor r raster For raster data processing i imagery For image processing v vector For vector data processing g general General file operation commands p paint Map design commands ps postscript Map design commands for postscript size db database Database management modules r3 voxel raster For 3D raster data processing 2 5 Help for using GRASS modules A help file is available for nearly all of the 400 GRASS modules in which the command and the syntax are described For using a module a short help is available using the parameter help d rast help Detailed descriptions and examples of a module that correspond to the help pages on the GRASS Homepage can be displayed with the command g manual module name g manual d rast Thereby a browser is started which displays the helping text An overall index is also integrated into the help which is also available at the end of this booklet see chapter 21 2 6 GRASS variables During a GRASS session some variables are set The can be printed and modified with the module g gisenv If the module is called without parameters GRASS displays the current environment variable settings g gisenv GISDBASE home holl grassdata GRASS_DB_ENCODING utf 8 MAPSET PERMANENT LOCATION_NAME spearfish GRASS_GUI tcltk GDF Hannover Courses 9 2 6 GRASS variables To display the current mapset the module needs to be called with the parameter MA
66. als must be achievable as quickly as possible Like already mentioned this is the simplest method of assignment without considering additional influencing factors such as speed or driving direction In this case additional parameters are imagin able which can be assigned to the module v net alloc via additional attribute columns v net alloc input hospitals_net output hospitals_alloc ccats 40 215 As a result subnets which are assigned to the hospitals by means of the determined costs are calculated from the roadnet Each road is therefore exactly assigned to the hospital for which the lowest costs arise due to the distance along the roadnet If required new nodes can be set within the vector in order to define an exact border GDF Hannover Courses 89 12 4 Assignment of the regions of optimal achievability ie E Ls re pe Ta a Bani Figure 26 Assignment of the next achievable roads to the hospitals D ARN N The result map of this example can be found in figure 26 The result can be displayed via d m interactive or via the command d vect d vect map hospitals_alloc color red cats 40 d vect map hospitals_alloc color green cats 41 d vect map hospitals_alloc color blue cats 69 GDF Hannover Courses 90 12 4 Assignment of the regions of optimal achievability d vect map hospitals_alloc color black cats 215 In total GRASS offers seven different network modules which are shortly introduced in chapter 11 1 Th
67. ap file TOP MODEL Exports a GRASS raster to a binary MAT File Raster File Series to MPEG Conversion Program Export GRASS raster as non georeferenced PNG image format Converts a raster map layer into a height field file for POVRAY Converts a GRASS raster file to a PPM image file at the pixel resolution of the CURRENTLY DEFINED REGION Converts 3 GRASS raster layers R G B to a PPM image file at the pixel resolution of the CURRENTLY DEFINED REGION Exports a GRASS raster file to a 8 24bit TIFF image file at the pixel resolution of the currently defined region Prosecution on next side GDF Hannover Courses 147 Command Prosecution description r param scale r patch r plane r profile r proj r quant r random cells r random r random surface r reclass area r reclass r recode r region r regression line r report r resamp rst r resample r rescale eq r rescale r ros Extracts terrain parameters from a DEM Uses a multi scalar ap proach by taking fitting quadratic parameters to any size window via least squares Creates a composite raster map layer by using known category values from one or more map layer s to fill in areas of no data in another map layer Creates raster plane map given dip inclination aspect az imuth and one point Outputs the raster map layer values lying on user defined line s Re project a raster map from one location to the current location This
68. apid and intuitive visualiza tion query and management of available data The functions are the following Display selected layers current region is used in order to display all in the display manager chosen maps see red box in the current set region and resolution Display selected layers default region is used in order to display all chosen maps in the total extent default region and the defined default resolution see g region d Display from saved region settings is used in order to display maps in a previously defined extent and resolution see g region help Erase to white is used for deleting the content of the current monitor in order to call a new map see d erase help GDF Hannover Courses 47 8 1 GIS Manager Zoom allows to zoom in and or out of map cutouts Thus it is important to take the assignment of the mouse buttons in the command interpreter into consideration Return to previous zoom zooms to the previously selected region Pan and recenter is used in order to pan in the currently displayed map Please pay attention to the notifications in the command interpreter Query map allows to query for raster and vector maps The results of the raster maps are shown in the command interpreter the results of the vector maps are visualized in a pop up window and can be modified according to the settings The respective map must be chosen before Add group is used in order to
69. ates two columns must be added to the attribute table This can be done using software such as OpenOffice or directly in GRASS create additional integer column in dBASE format echo ALTER TABLE lt vectormap gt ADD COLUMN lt column gt integer db execute Add vector length v to db map lt vectormap gt option length units meters col1 lt column gt Query for verification echo SELECT FROM lt vectormap gt db select 10 3 3 Manipulating vector attributes GRASS also offers the possibility of manipulating vector attributes Attributes can be updated ac cording to different query criteria via the SQL command UPDATE GDF Hannover Courses 68 10 3 Managing vector attributes update column area larger than 200 echo UPDATE lt table gt SET attributei 2 WHERE area gt 200 db execute If PostgreSQL is used as attribute storage more SQL commands are available via the commandline tool psql which comes with the postgres distribution It offers the possibility to update entries based on calculating results The above examples could be changed to the following update column area larger than 200 based on calculations echo UPDATE lt table gt SET area area 1000 WHERE area gt 200 psql d lt PG database gt Manipulating vector attributes interactively is also possible The vector file is opened and queried by the module d what vect The attributes are displayed in a separate popup wi
70. auptdreiecksnetz SPHEROID bessel 6377397 155 299 1528128000033 TOWGS84 590 5 69 5 411 6 0 796 0 052 3 601 8 3 PRIMEM Greenwich 0 UNIT degree 0 0174532925199433 PROJECTION Transverse_Mercator PARAMETER latitude_of_origin 0 PARAMETER central_meridian 9 PARAMETER scale_factor 1 PARAMETER false_easting 3500000 PARAMETER false_northing 0O UNIT meters 1 Origin 3368561 280000 5928333 120000 Pixel Size 0 32000000 0 32000000 Corner Coordinates Upper Left 3368561 280 5928333 120 Lower Left 3368561 280 5927132 160 Upper Right 3369703 680 5928333 120 Lower Right 3369703 680 5927132 160 Center 3369132 480 5927732 640 7d 1 12 86 E 53d28 18 24 N 7d 1 14 67 E 53d27 39 41 N 7d 2 14 77 E 53d28 19 26 N 7d 2 16 56 E 53d27 40 43 N 7d 1 44 71 E 53d27 59 33 N 1N FPN EO TN OES GDF Hannover Courses 18 4 2 Projections It is important that such information is precisely controlled and scrutinized and that they should be available as completely as possible Small deviations an incorrect DATUM or SPHEROID can produce enormous deviations in data positioning 4 2 Projections Before creating your own project region Location it is important to consider which projection will be used The following chapters will give a brief introduction to the most common projections their properties and parameters Figure 10 show
71. ause sites are saved as vector data in GRASS 6 0 14 1 2 Regular splines with tension interpolation The splines interpolation approximation method is also appropriate for filling up large data blanks During this method a thin surface is created which passes through or near the available data points The target is that the surface clearly represents the available data points and closes the data blanks In order to receive a reasonable result of interpolation it is necessary to familiarize with the individual modules and the parameters of usage Further details for optimizing the interpolation parameters can be found in 7 Based on the vector data the following modules calculate a Splines with Tension Interpolation result ing in a raster model including simultaneous conversion GRASS modules for RST Interpolation v surf rst v vol rst G3D grid volume Like mentioned before in chapter 14 1 1 sites are now handled as vectors in GRASS The RST interpolation module has accordingly been reshaped for the sites as v surf rst Further GRASS modules for the interpolation surf area surf contour r r r surf fractal r surf gauss r surf random 14 2 Data interpolation into the vector format The point information e g measurement values representative for a region can be conducted via the area by using the Thiessen Polygon Calculation GDF Hannover Courses 97 14 2 Data interpolation into t
72. base map r basins fill Generates a raster map layer showing watershed subbasins r bilinear Bilinear interpolation utility for raster map layers r blend Blends color components of 2 raster maps by a given first map r buffer Creates a raster map layer showing buffer zones surrounding cells that contain non NULL category values r cats Prints category values and labels associated with user specified raster map layers r circle Creates a raster map containing concentric rings around a given point r clump Recategorizes data in a raster map layer by grouping cells that form physically discrete areas into unique categories r coin Tabulates the mutual occurrence coincidence of categories for two raster map layers r colors Creates Modifies the color table associated with a raster map layer r composite Combines red green and blue map layers into a single composite map layer r compress Compresses and decompresses raster files Prosecution on next side GDF Hannover Courses 145 Prosecution Command description r contour Produces a GRASS binary vector map of specified contours from GRASS raster map layer r cost Outputs a raster map layer showing the cumulative cost of moving between different geographic locations on an input raster map layer whose cell category values represent cost r covar Outputs a covariance correlation matrix for user specified raster map layer s r cross Creates a cross product of
73. color or creating short picture animations The conirol window features contain Auto Clear Clear Surface Vectors Sites Volumes Cancel XY position Height look here look cancel zexag Perspective Twist Reset If active the graphic window is automatically cleaned before a surface sur face appears Cleans the graphic window with background color Shows loaded raster surface with currently set options Shows loaded vector map on the surface Shows loaded sites map vector points on the surface Shows loaded volume maps volume surface in 3 dimensional space Stops the calculation of the display Contains a point which represents the viewer The position of the viewers can be changed by clicking on it Regulates the height position of the viewers Allows that the user can click on a point of the data surface which remains central even if the position of the viewer has changed Cancels the look here feature standard Manipulates the vertical dimension of the surface The x y and z values are set equal by the value 1 0 If for instance the eastings and northings are indicated in meters and the height is however indicated in feet the zexag value 305 would display the true dimensions of the surface Due to the rising of the model zexag gt 1 0 a falsification takes place but the visual output is mostly more representative Displays the viewing angle Displays the dispos
74. considered free software Free software is a matter of liberty not price To understand the concept you should think of free as in free speech not as in free beer Free software is a matter of the users freedom to run copy distribute study change and improve the software More precisely it refers to four kinds of freedom for the users of the software e The freedom to run the program for any purpose freedom 0 e The freedom to study how the program works and adapt it to your needs freedom 1 Access to the source code is a precondition for this e The freedom to redistribute copies so you can help your neighbor freedom 2 e The freedom to improve the program and release your improvements to the public so that the whole community benefits freedom 3 Access to the source code is a precondition for this A program is free software if users have all of these freedoms Thus you should be free to redistribute copies either with or without modifications either gratis or charging a fee for distribution to anyone anywhere Being free to do these things means among other things that you do not have to ask or pay for permission You should also have the freedom to make modifications and use them privately in your own work or play without even mentioning that they exist If you do publish your changes you should not be required to notify anyone in particular or in any particular way The freedom t
75. ct grey grey eq grey log byg byr gyr rainbow ramp random ryg wave rules rules options aspect bcyr byg byr elevation evi grey gyr rainbow ramp ryg slope srtm terrain wave By indicating the variable rules we can assign our own colortable colors map geology color rules lt lt EOF 100 200 0 255 130 7 100 129 187 222 180 39 43 18 200 EOF ON OOP HK For transferring the colortable from one rastermap to another or for assigning an individual or already specified colortable use the module r colors with the parameter rast r colors rastermap rast orig_rastermap The newly assigned colortable can be visualized via the module d colortable d colortable rastermap 9 5 Map statistics GRASS also offers built in modules for calculating map statistics In addition a direct interface to the statistical software R exists for more complex geostatistic analysis see bibliography Histograms and pixel distributions Information about image histograms and image statistics are important for image improvement and image analysis contrast adjustment stretch operations Image histograms can be generated using the module d histogram d histogram rastermap In the interactive mode the pixel distributions are represented in terms of bars It is also possible to display the result as a pie chart GDF Hannover Courses 57 9 5 Map statistics The module r stats is presents the pixel distribution as table This module is very ext
76. d animations For this purpose the module NVIZ is internally available and compatible to Free Software programs like Vis5D and Vis5D 16 1 Displaying a 3D map with NVIZ NVIZ is a tool generated from the module SG3d for visualizing 3 dimensional raster data vector data and or sites as well as for 3D queries and creating picture animations File Panel Scripting Auto W Clear Feature W Surface W Vectors W Sites W Volumes DRAW Clear Cancel View eye center LOOK here height zexag _ 22250 00 10 00 center top cancel Zl perspective 40 0 E RESET 0 0 twist Figure 30 NVIZ graphical control window Before starting the program the resolution of the running GRASS region is supposed to be verified because it determines the maximum possible resolution in NVIZ Large region dimensions such as a 1000 x 1000 w h size decelerate the processing speed of NVIZ The module can either be started by indicating the map to be loaded GDF Hannover Courses 103 16 1 Displaying a 3D map with NVIZ nviz elev elevation_map or with the parameter q Parameter q Quickstart elevation optional name of a GRASS raster map as z value relation vector optional name of a GRASS vector map After starting NVIZ a graphic window and a control window is opened in which the individual features are displayed From the control window additional menu windows can be started e g color selection background
77. d for any textual work regardless of subject matter or whether it is published as a printed book We recommend this License principally for works whose purpose is instruction or reference APPLICABILITY AND DEFINITIONS This License applies to any manual or other work in any medium that contains a notice placed by the copyright holder saying it can be distributed under the terms of this License Such a notice grants a world wide royalty free license unlimited in duration to use that work under the conditions stated herein The Document below refers to any such manual or work Any member of the public is a licensee and is addressed as you You accept the license if you copy modify or distribute the work in a way requiring permission under copyright law A Modified Version of the Document means any work containing the Document or a portion of it either copied verbatim or with modifications and or translated into another language GDF Hannover Courses 131 A Secondary Section is a named appendix or a front matter section of the Document that deals exclusively with the relationship of the publishers or authors of the Document to the Document s overall subject or to related matters and contains nothing that could fall directly within that overall subject Thus if the Document is in part a textbook of mathematics a Secondary Section may not explain any mathematics The relationship could be a matter of histo
78. d remote sensing Hanover July 2005 1 Introduction Today Free Software has become a synonym for innovation and progress Free use modification and distribution of the programs and their open source codes are guaranteed due to the support of free idea exchange between users and developers This means a steady worldwide organized and demand oriented advancement in short periods of time for the Geographical Information System GRASS GIS This document offers a short introduction in the Geographical Information System GRASS It ex tends the known German and English literature 5 A by aspects of the use and the installation of GRASS 6 0 In addition modified material for using the latest GRASS developments is therefore handed out from the date of publication Before reading this script we want to introduce you a little insight and view in the future of GRASS GIS by the help of a Roadmap Fig 11 It shows the directions in which GRASS development has been moved since 2001 and will move in the future Roadmap GRASS GIS Development 6 5 7 5 1 x 5 0 5 1 code mix CVS HEAD 6 0 5 0 x CVS HEAD 2o Ne a Ng 5 0 x 5 4 x CVS release branch l CVS release branch 5 0 2 5 0 3 Figure 1 Roadmap of the GRASS development since 2001 Status 1 2005 5 4 0 GDF Hannover Courses 1 2 Design and Structure GRASS is a hybrid and modular structured GIS with raster oriented and vector oriented functions Each fu
79. define a map group for visualization This map group can be saved as a kind of project wherever you like It is recommended to save it in the directory of the current mapset Add raster makes the call of a new raster map possible Add vector makes the call of a new vector map possible Add paint label is used in order to integrate images into the map which are stored in the paint labels folder See v label Create new command makes possible to define commands or even command sequences which can be recalled with a mouse click Digitize vector map is used in order to change the geometries of vector maps loaded in d m Thus the digitalizing module v digit is started The respective map must be chosen with the mouse before Cut selection allows to delete maps or also commands from the GIS manager These maps are still available in the location For deleting maps from the databasis it is necessary to use the module g remove Create new workspace file makes possible to create a kind of project file in which maps are saved including their color assignments visualization sequence and so on Open an existing workspace file is used in order to recall a project file in which maps are saved including their color assignments visualization sequence and so on Save workspace file is used in order to save a created project file in which maps are saved including their color assignments visualization sequence and so on Print map
80. e 125 18 6 Geospatial bookmarks sua ak ee e we ek ee Re a RR eH 125 18 7 Creating analog maps with QGIS a oaoa 2 ee 126 19 Definition of Free Software 128 20 GNU Free Documentation License 131 21 Command index 139 Cited literature 155 GDF Hannover Courses vi List of Figures List of Figures 1 Roadmap of the GRASS development since 2001 Status 1 2005 See ee E 1 2 _ Geometry and attribute data within Geographical Information Systems 3 3 Comparison of raster and vector data types in an identical aay ea wives ect Se 4 4 Data dimensions in GIS 2 35 4 eB e oo el ae Bae we HS 5 5 _ Example structure of a GRASS 6 0 database 004 6 6 _ Innovations between GRASS 5 4and6 0 2 20000 ees 11 7 _ TcelTk start screen in GRASS 2 16 8 _ Screen for defining a new Location in GRASS ooo 17 9 Screen for integrating an EPSG codel aoo sooo 2 0000 ee eee 17 10 _ Projection of the earth s surface on a map a saosaoa 19 11 _Various projection models cylindric conic and azimuthal ee ee e ere 21 12 Specifications to the extent of the project region and grid resolution
81. e downloaded at http grass itc it download data php Importing the TK24 into the Spearfish dataset Download Spearfish demonstration location and TK24 wget http grass itc it sampledata spearfish_grass57data tar gz wget http grass itc it sampledata spearfish_toposheet tar gz Unpack Spearfish location in grassdata and start GRASS tar xvzf spearfish_grass57data tar gz home user grassdata grass60 home user grassdata spearfish57 PERMANENT Importing TK24 GeoTiff into the location tar xvzf spearfish_toposheet tar gz r in gdal e in spearfish_topo24 tif out tk24 Visual control GDF Hannover Courses 78 11 6 Digitizing with GRASS g region rast tk24 ap d mon x0 d rast tk24 For training purposes the local recreation area around Lookout Peak east of Spearfish is supposed to be recorded In order to register points lines and area data the point of interest Lookout Peak height information and forest areas are digitized into three thematic maps see figure 21 Figa iler i cS i Figure 21 Topographical map of the Spearfish region including landuse information To save the newly created vector data in a separate user specific mapset you need to exit GRASS in order to exit the location PERMANENT and start again with a new mapset Exit GRASS exit Start GRASS again and create a new mapset grass60 indicate the new name of the mapset in GUI or in the console STRG ESC
82. e module is implemented via a separate graphical menu in which the most important features are integrated as buttons EVA ale RA s aa ae Middie mouse button Right mouse button Figure 20 Digitizing GUI of the module v digit Before introducing a short example illustrating the usage of the new digitizing module all important features and their properties are described briefly by means of figure 20 from left to right Digitize new point is used in order to digitize a new vector point The module function options are layer allocation to be chosen and the category value of the point In this case the following possibilities are available no category manual entry and next not used If an ap propriate attribute table is available in the database it is automatically opened after the feature has been digitized see figure 23 These options also apply to Digitize new line Digitize new boundary and Digitize new centroid described below Digitize new line is used in order to digitize a new vector line Digitize new boundary is used in order to digitize a new closed boundary vector line If an ap propriate attribute table is available in the database it is automatically opened after the feature GDF Hannover Courses 76 11 6 Digitizing with GRASS has been digitized If an area is digitized the attributes to be allocated to this area are not con nected to the boundary but to a ce
83. e usage is always similar so that this application example is representative for the other v net x modules GDF Hannover Courses 91 13 Data conversion It is frequent that vector data are supposed to be created from raster data lines or areas In the reverse case vector data for instance contour lines are to be converted in the raster model in order to interpolate a relief model As a hybrid GIS GRASS offers the possibility to convert data from one data model into an other 13 1 Vectorization of raster data In GRASS raster data can automatically be converted into the vector model This conversion can be conducted in continous as well as in linear and isolinear structures GRASS Rasterdata GRASS Vectordata r to vect feature area r thin r to vect feature line v digit handcrafted Figure 27 Modules for converting raster data into vector data Vectorization into lines and isolines GRASS offers two interesting modules for converting linear raster data automatically into vector lines or isolinevectors These are r to vect as well aS r contour For the conversion into vector lines the module r to vect can be used In this case the module supports the geometry types line polygone and site whereby line is set by default If the lines are too wide in the available raster format several pixels the lines have to be thinned out in the raster file to the width of one pixel by the module r thin before starting the
84. eady available raster map as mask via the command g copy For this purpose the map must be named MASK capital letters in order to pose as mask All values that are not NoData NULL are used as mask values All other values are used during any analysis Masks can also be created via the module r mapcalc Simple copying of a map as mask r mapcalc MASK map More complex operations for creating a mask only mask where category value 1 and 3 are present r mapcalc MASK if map 1 map 3 nu11 map GDF Hannover Courses 101 15 4 Masking As an example we will do a rasterbased analysis on the spearfish sample dataset only on this areas of the map geology where an owner is registered in map fields Create mask for areas in map fields r mapcalc mask_map if fields 1 nu11 g copy rast mask_map MASK Control d rast geology Now only the geological areas with a valid user registered in the rastermap fields are visible It must be taken into consideration that a mask that is set will be applied to all raster analysis vector analysis are not concerned If the mask is not used anymore the map MASK must be deleted see chapter 9 6 2 In case a mask is set the comment Raster MASK present always reminds you in the prompt GDF Hannover Courses 102 16 3D visualization and animation Besides the creation of 2D maps GRASS also provides the possibility to create 3D visualizations an
85. ensive with many application possibilities Therefore have a look at the help page before using this module For instance multiple rastermaps can be queried simultaneously r stats rastermap The module r report which reverts to r stats can conveniently be used in this context This module is able to display interactively controlled pixel distribution area analysis and so on as table As an example a query of the landuse and geology is shown g region rast landuse p r report hen landuse geology units h 1lresidential 676 00000 A PeaSSan ena an es E 1 metamorphic 23 00000 3l igneous 18 00000 4 sandstone 125 00000 5 limestone 70 00000 6 shale fee ae is a Oe A a a a A ee es ee 4 2500000 Pied y shale ge ee Ge es oh a wh gh ot Me oe ee Ee al 29 000001 8lclaysand 14 00000 I9lsand citar Fee een ahh howe eve er Tee ee AL ly 42 00000 a aR Ce 25 2 commercial and services 115 00000 i eo ca E Sate sae 1 metamorphic 16 00000 4 sandstone 19 00000 eral A a ba ape a eae ar a Sasa 8 transportation and utilities 400 00000 SSR eROR SS aa ess Se E pos SaaS 4 sandstone tee ew we we 34 000001 li bUPimestones cate ae Bo aoe Boo ek A ae al 8 00000 6 shale 104 00000 7 lsandy shale 26 00000 8lclaysand 4 00000 I9lsand 224 00000 GDF Hannover Courses 58 9 6 Methods for manipulating rastermaps T
86. ent raster formats Generally three format types should be considered Image format The individual rasters always have positive integral values in the known pixel based image formats such as PPM PNG JPEG and GIF ASCII format The individual rasters of the ASCII format can contain positive and negative integral values as well as floating point values The ASCII GRID of Arcinfo is an example of this format Binary format In the binary raster format the individual pixels with positive and negative integral values or floating point values can also be saved in different channels with different resolutions Geo TIFF or ERDAS IMG are examples for this format Now it is time to mention a property of GRASS GIS related to raster data import raster maps are always imported with their original resolution and border coordinates but they are exported with the current resolution and border setting of the region see chapter 7 1 For importing non georeferenced data there are two cases to be considered 1 If the location including resolution is defined and the map has to fit in the scan resolution complies with the required resolution GRID RESOLUTION 2 If the parameter of the location can comply with the map to be imported especialy the resolu tion it has to be installed in such a way that the image can be imported unchanged Table 7 gives a list of modules used to import raster data in different formats i e formats of other
87. ersion by various parties for example statements of peer review or that the text has been approved by an organization as the authoritative definition of a standard You may add a passage of up to five words as a Front Cover Text and a passage of up to 25 words as a Back Cover Text to the end of the list of Cover Texts in the Modified Version Only one passage of Front Cover Text and one of Back Cover Text may be added by or through arrangements made by any one entity If the Document already includes a cover text for the same cover previously added by you or by arrangement made by the same entity you are acting on behalf of you may not add another but you may replace the old one on explicit permission from the previous publisher that added the old one The author s and publisher s of the Document do not by this License give permission to use their names for publicity for or to assert or imply endorsement of any Modified Version GDF Hannover Courses 135 COMBINING DOCUMENTS You may combine the Document with other documents released under this License under the terms defined in section 20 above for modified versions provided that you include in the combination all of the Invariant Sections of all of the original documents unmodified and list them all as Invariant Sec tions of your combined work in its license notice and that you preserve all their Warranty Disclaimers The combined work need only contain one copy
88. es Basically it is usefull to keep control about the Polygon Resolution A high polygon resolution lt 3 leads to longer computation times on not up to date computers and therefor should be avoided GDF Hannover Courses 105 16 2 Displaying raster volume layers VOXEL Figure 32 Different precipitation levels above Slovakia The dataset shown in this application was produced by 4 and can be downloaded as a ready to use GRASS location from the site of GDF Hannover bR see 9 GDF Hannover Courses 106 16 3 Creating an animation 16 3 Creating an animation Besides the simple visualization NVIZ can also be used in order to create and display animated data This is especially reasonable when time periods are supposed to be analyzed NVIZ offers the possibility to create a simple fast animation via the graphical user interface or a professional script based variant Now this simple variant is supposed to be introduced Animation Panel 4 m b p Tot Frames 25 0 E TPRR TAT PATNA TOTO Key Frames Ada Clear All Show J Path J Vect _ Sites Tension intep Linear Spline gt a Run and Save Close Figure 33 Creating a simple animation in NVIZ The control window for creating an animation can be found in the menu Panel gt Animation see figure 33 The total number of images to be used for the animation is indicated at first In o
89. es of the project region are defined The entry is in meters which means a 7 digit number for the northern value and a 6 digit for the eastern value Here is an example of a UTM project region g region p projection 1 UTM zone 32 datum potsdam ellipsoid wgs84 north 6100000 south 5880000 west 500000 east 630000 nsres 12 5 ewres 12 5 rows 17600 cols 10400 4 5 5 Creating a latitude longitude project region A latitude longitude location contains data in latitudes and longitudes 0 90 north and or south 0 180 east and or west expressed in the sexagesimal system degree minutes seconds letter indicating the orientation or decimal system pos neg decimal degrees The entry of the border coordinates and standard raster resolution can be in the decimal degrees system or sexagesimal system coordinate system for location latitude longitude B Here is an example of a lat lon project region g region p GDF Hannover Courses 30 4 6 Deleting maps and projects projection 3 Latitude Longitude zone 0 datum unknown default WGS84 ellipsoid unknown default WGS84 north 90N south 90S west 180W east 180E nsres 0 04 48 ewres 0 04 48 rows 2250 cols 4500 4 6 Deleting maps and projects In order not to destroy the internal structure of the GRASS database the command g remove is to be used for deleting single maps within a mapset It is not recommended to delete files w
90. es or B using an existing reference map in the target location GDF Hannover Courses 40 6 2 Georeferencing procedure GRASS 5 0 2 cvs Monitor x0 LWIT ZOA Figure 14 Searching control points of a scanned topographical map with the GRASS module i points A If control points for georeferencing are known e g from an available analog paper map clearly identifiable points such as GauB crosses or indicated edge coordinates are chosen by clicking on the imported map and entering the coordinates in X term separated by a space B If a georeferenced map exists in the target location which exhibits distinctive points such as crossroads or buildings and which can also be found in the map to be referenced the georeferenced map can be loaded into the right window with the PLOT RASTER function Thus it is possible to find and to mark corresponding reference points in both monitor windows The ZOOM function allows exact placement of control points see Figure 14 The control points should be evenly distributed throughout the map The RMS error can be deter mined via the ANALYSE function which should not be higher than half of the raster resolution of the target location All partial RMS errors are calculated to an overall error Where required it is GDF Hannover Courses 41 6 2 Georeferencing procedure possible to ignore or reassign an inexactly assigned contr
91. essing maps with Skencil 17 5 Processing maps with Skencil An additional possibility for producing maps is the free drawing program Skencil 22 This python based program offers a Geo Object Plugin as enlargement so that ESRI SHAPES can be red SHAPES can directly be overlain This is possible by geo information in the SHAPE data In order to use the Geo Object Plugin SHAPElib library 21 and the necessary python connections 18 have to be installed as well TEE 00 db S O Rah D y Y TB 300 200 alisa jas3 bss des o gt Ki a gt o Osnabr ck Daten in Skencil hp joinea porjoinea shp Browse import as is fit to page register with selected x Ausw hlen ge ndert 54 1 140 0pt 640 0pt Figure 39 Skencil with Geo Object Plugin at the example of the FRIDA dataset of Osnabrueck Skencil also supports importing Xfig files GDF Hannover Courses 116 18 QGIS The free geodata viewer QGIS 19 offers direct access the GRASS database For this purpose an appropriate plugin is available for vector data GRASS raster data are connected in QGIS via the already mentioned GDAL suite 11 Furthermore all vector formats supported by OGR and raster formats supported by GDAL are also readable in QGIS Thus all data available in the current GRASS location are also available for the visual
92. f 12 cm per kilometer at the outer meridian stripes because a diagonal axial mercator projection is conducted at each single meridian stripe The extent complies to 100 km in each direction of the main meridian Thus an overlapping of the individual meridian stripe systems of approx 23 km occurs The northings on the main meridian are seen as the distance from the equator In order to GDF Hannover Courses 24 4 5 Creating different project regions in GRASS avoid negative values with the easting the value 500000 m is adopted for the main meridian Based on this the distance in meters between a given point and the main meridian can be calculated by reducing or adding 500000 from the easting value A number derived by the decimal degree of the main meridian divided by 3 is added at first order Northing is always calculated as distance from the equator LUneburg lies e g in the system of the 9th longitude on 3593000 5902000 easting northing and in the system of the 12th longitude on 4392753 5902298 easting northing UTM coordinate system The UTM System Universal Transverse Mercator is currently based on the WGS84 ellipsoid The earth is covered by 60 meridian stripes between 84 northern latitude and 80 southern latitude These stripes are 6 longitudes wide each An intersection cylinder is used for the projection in order to avoid distortions of the longitudes at the border meridians Thus the central meridian is not equidistan
93. for creating a new Location are entered as described in chapter 4 5 1 GDF Hannover Courses 16 4 1 Calling up a GRASS project P dassau berlin gdf cvs g57 images Befehisfenster Konsol MEE Sitzung Bearbeiten Ansicht Lesezeichen Einstellungen Hilfe GRASS 5 7 cus LOCATION This is the name of an available geographic location spearfish is the sample data base for which all tutorials are written MAPSET Every GRASS session runs under the name of a MAPSET Associated with each MAPSET is a rectangular COORDINATE REGION and a list of any new maps created DATABASE This is the unix directory containing the geographic databases The REGION defaults to the entire area of the chosen LOCATION You may change it later with the command g region LOCATION osnabrueck Center list for a list of locations MAPSET PERMANENT or mapsets within a location DATABASE gdf grassdata AFTER COMPLETING ALL ANSWERS HIT lt ESC gt lt ENTER gt TO CONTINUE OR lt Ctr1 C gt TO CANCEL Befehlsfenster Befehlsfenster 2 Figure 8 Screen for defining a new Location in GRASS B If an EPSG code is exists for the project Location it can be used to create a new Location automatically Click with the mouse on the button Create Location from EPSG and enter the appropriate code number see Fig 9 The button EPSG Codes lists existing codes with their appropriate definitions ur Epsg Sett
94. formation could then be used to adapt them to a particular situation This application is also explained in detail in chapter 12 11 1 3 Minimum Steiner Tree Problem The Minimum Steiner Tree describes the optimal connection of nodes within a network star The following example should help to make this clear Lets say Several hospitals distributed in a city need new network cables for telemedicine services The target is to lay the necessary cable as good as possible along the available roads so that only few cable is needed and all hospitals are connected to the new cable network The GRASS module v net steiner is available for these tasks 11 1 4 Travelling Salesman Problem This question contains the determination of a perfect route between different points excursion For instance the hospitals distributed in a city which are supposed to be visited by a pharmarceutical company representative The GRASS module v net salesman calculates the perfect path for the traveler which could be either the shortest path by distance or time v net salesman in hospital_net out pharmarepresentative ccats 40 215 11 1 5 Cost analysis The GRASS module v net iso creates cost analysis on a vector network This means a calculation of iso distances which can be considered as a calculation of concentrical distances around a point Thus run length e g for sewage channel systems can be calculated based on the vector length or other attributes
95. ge space file size 6 1 1 The optimal scan resolution If an analog map is to be imported into GRASS GIS the scan resolution of the map also determines the resolution of the location which is to be chosen This may seem very simple but requires some trial and error to find the balance between not too high file size and not too low data loss scan value The following example shows how to proceed in order to adjust the location optimally on the GDF Hannover Courses 38 6 1 Preparation for georeferencing geodata or vice versa a Sample calculation of the resolution for a 300dpi scan 300dpi 300rows 2 54cm 118 11rows cm b Calculation of the compatible raster resolution for a 1 25000 map scale Route_in_nature scan rows_per_cm 25000cm 118 11rows 2 12m row If the location with its resolution is already defined a conversion between scan resolution and geo graphical resolution will be oe to determine the value for the scan resolution The example shown above is thus counted back 5 6 1 2 Creating the needed project regions The first step is to create a XY location for the scanned raw map to be imported The extent of the project region should at least comply with the number of pixel in X rows height and Y columns width direction of the map to be imported e g use xv for determination It is important that the XY location be large enough to accomodate the raw data GRASS allows the locations to be large
96. gical operations are offered which are briefly introduced break breaks overlaying lines at their intersection points and displaces them by a node rmdupl deletes lines that occur twice Please handle the attributes with care rmdangle deletes so called dangles Please consider the indication of the threshold chdangle changes the data type of the so called dangles from boundary into line Please consider the indication of the threshold rmbridge deletes topologically illegal connections between an area and an isle or between two isles chbridge changes the data type of a connection between an area and an isle or two isles from boundary into line snap depending on the threshold lines are connected with the next following vertices GDF Hannover Courses 75 11 6 Digitizing with GRASS rmdac deletes centroids in polygons that occur twice bpol topological clean up of data which do not have their own topology e g SHAPE Creating a new topology with clean vertex to line transitions prune deletes vertices depending on the indicated thresholds of lines and boundaries without changing or damaging the topology rmarea deletes micro areas depending on the indicated thresholds and allocates them to the biggest adjacent area rmsa makes small angles disappear between lines and nodes 11 6 Digitizing with GRASS During the redesign of the vector features the digitizing module v digit has also been rewritten Th
97. gion The border coordinates are defined by the pixel extent of the non referenced map s to be imported These can be determined among other things with the program xv Windows gt Image Info Starting from the defined attachment in the left edge below only a north and an east value is added according to the rows and columns of the original picture The raster resolution must consequently be 1 This procedure will be discussed again in the context of georeferencing a scanned map see chapter 6 Here is an example of a XY project region g region p projection 0 x y zone O north 8000 south 0 west O east 8000 nsres 1 ewres 1 rows 8000 cols 8000 4 5 4 Creating an UTM project region The creation of an UTM location Universal Transverse Mercator resembles the creation of a Gau Kr ger location but with a smaller cylinder In this case it is not referred to a Ber hrzylinder with the basic bessel ellipsoid but to a Schnittzylinder with the basic WGS 84 ellipsoid With respect to the GauB Kriiger projection the parameters that have changed are shown below GDF Hannover Courses 29 4 5 Creating different project regions in GRASS coordinate system for location UTM C specify ellipsoid name z B wgs84 world geodetic system 1984 do you want to specify a map datum for this location z B wgs84 Enter Zone 32 UTM zone for Germany Is this South Hemisphere n Afterwards the coordinat
98. graphic index In a tan beta map from elevation map Simulates TOPMODEL which is physically based hydrologic model Outputs raster map layer values lying along user defined transect line s Calculates univariate statistics from the non null cells of a raster map calculates univariate statistics from a GRASS raster map Watershed basin creation program Watershed basin analysis program Queries raster map layers on their category values and category labels r3 commands Command Description r3 in ascii Convert a 3D ASCII raster text file into a binary 3D raster map layer r3 in v5d import of 3 dimensional Vis5D files i e the v5d file with 1 variable and 1 time step r3 info Outputs basic information about a user specified 3D raster map layer r3 mapcalc r3 mapcalc r3 mask Establishes or removes the current working 3D raster mask r3 mkdspf Prosecution on next side GDF Hannover Courses 150 Prosecution Command description r3 null Explicitly create the 3D NULL value bitmap file r3 out ascii Converts a 3D raster map layer into an ASCII text file r3 out v5d Export of GRASS 3D raster file to 3 dimensional Vis5D file r3 timestamp print add remove a timestamp for a 3D raster map v commands Command Description v buffer Create a buffer around features of given type areas must contain centroid v build all v build all v build Creates topology for GRASS vector data v bui
99. gt database scheme UNIX User gt database user UNIX Group gt database group Now it is possible to grant certain permissions to groups corresponding to mapsets and location Inside GRASS the module g access is available Please keep in mind that Unix and database users must be synchronized manually This is impor tant when removing a Unix user The corresponding database user needs to be removed manually by the administrator as well 10 3 1 Display attributes The module v db select provides a basic report of vector attributes inside the console All attributes will be printed separated by defined field separator Print attributes of vector map roads v db select map roads fs GDF Hannover Courses 67 10 3 Managing vector attributes cat label Olno data 1 interstate 2 primary highway hard surface 3 secondary highway hard surface 4 light duty road improved surface 5 unimproved road 10 3 2 Adding attributes The module v to db allows the addition of helpful attributes to the vector objects These are e clear category values as long as these are not already available cat means IDs e coordinate pairs coords e area sizes of the polygons provided with a centroid area e length of the vector lines length e number of features per category count e categories of the left and right limiting areas sides e results of a query query However an additional column in the case of point coordin
100. h none one or several attributes property For administation in GRASS the dBase data format is used by default Interfaces to different external DBMSs Database Management System like data bases e g PostgreSQL MySQL Oracle and so on are also available In comparison to raster data vector data are characterized by their comparatively low memory requirements and short computing times for conducted analyses Unlike raster data vector data have a topology which means that the lines and areas know which nodes they possess and or on which areas they border Point data Sites can be considered as a special form of vector data They are used for saving selectively spread spatial information This data type can be saved as vector sites in GRASS 6 0 but not in version 5 4 Accordingly it has the properties of vector data Attribute data categories are attributes which are interconnected with the data types mentioned above They are mostly saved within GIS or in a database system coupled with GIS via DBMI Database Management Interface GDF Hannover Courses 3 2 2 Data dimensions in GIS Graphics data eventually describe the method how a spatial object is displayed under a certain topic on acertain output device monitor plotter etc In GIS they are qualitatively and quantitatively set in relation as specimen via the combination of the described data types These phenomenons and objects entities to be saved in a GIS occur in two
101. he minimum number of control points needed by polynomial degree is given in table 9 Polynomial degrees of first to third order are proven of value Whereby at polynomial degrees of third order more than 10 control points are required GDF Hannover Courses 43 7 Data export The data export is naturally just as important for working in GIS as the data import described in chapter 5 There is a possibility between the export of data in exchange formats which are further to be processed with other GIS software or the export in image formats for a professional visualization with external graphic software such as Xfig or Skencil GRASS offers a range of modules which can export raster data vector data and sites The respective command syntax can be learned or like all the other modules printed with the parameter help 7 1 Exporting raster formats In table 10 those modules are listed which can export GRASS raster data into different external formats Besides this formats of other GIS systems and also special exchange formats of remote sensing data belong to these modules Table 10 A range of modules for exporting raster data GRASS Export Module commands Raster formats r out arc ARC INFO ASCII GRID r out ascii ASCII r out mpeg MPEG r out png PNG see also d mon PNG DRIVER with True Color Support r out pov POV r out ppm PPM PNM r out tiff TIFF TFW r
102. he vector format Before calculating area polygons from perpendicular bisectors of the side Thiessen polygons via Inverse Distance Weight IDW interpolation sites with z information needs to be digitized manually Eventually the given resolution needs to be adopted by g region v surf idw in point file out output file Thiessen npoints 1 In this case different application methods of the triangulation are carried out For further information it is reasonable to have a look at the manual pages g manual v surf idw GDF Hannover Courses 98 15 Raster map arithmetic with r mapcalc The module r mapcalc is used for manipulating analyzing and producing raster maps via arithmetical operations It can interactively been started or directly been used at the prompt Existing raster maps constants integer values or floating point values as well as features can therefore be used In GRASS no values and values with the 0 value are differentiated as follows NULL no data Zero 0 data e g freezing point in Celsius The usage of r mapcalc presupposes knowledge concerning image formats map projections and the currently set extend of the project region region Before using it is recommended to have a look at the help pages because this module is very powerful 15 1 Operators in r mapcalc Table 12 Operators in r mapcalc Operator Meaning Type Priorit
103. hen redistributing the program you cannot add restrictions to deny other people the central freedoms This rule does not conflict with the central freedoms rather it protects them You may have paid money to get copies of free software or you may have obtained copies at no charge But regardless of how you got your copies you always have the freedom to copy and change the software even to sell copies Free software does not mean non commercial A free program must be available for commer cial use commercial development and commercial distribution Commercial development of free software is no longer unusual such free commercial software is very important Rules about how to package a modified version are acceptable if they don t substantively block your freedom to release modified versions Rules that if you make the program available in this way you must make it available in that way also can be acceptable too on the same condition Note that such a rule still leaves you the choice of whether to publish the program or not It is also acceptable for the license to require that if you have distributed a modified version and a previous developer asks for a copy of it you must send one or that you identify yourself on your modifications In the GNU project we use copyleft to protect these freedoms legally for everyone But non copylefted free software also exists We believe there are important reasons why it is
104. hod NN 2 Splines Interpolation Regularized Splines with Tension RST Two GRASS interpolation modules can be used for the second mentioned application 1 Inverse Distance Weighted IDW 2 Splines Interpolation Regularized Splines with Tension RST 14 1 1 Inverse Distance Weighted This locally working interpolation method is based on the following assumptions The nearer a point to be interpolated is located to a point with known value the more similar is the value of the point to be interpolated to the known value in close distance At first the distance between the point searched for and the surrounding support points is therefore calculated In the following the calculation of the point searched for is conducted as mean value of the surrounding support points The weighting is the reciprocal value of the distance 1 d Mostly the distance is exponentiated depending on the respective properties of the underlying true surface 1 d2 or 1 d3 Good knowledge about the surface to be interpolated is necessary in order to guarantee an optimal area result via interactive control of the interpolation parameters The output file is a raster map GDF Hannover Courses 96 14 2 Data interpolation into the vector format GRASS module for the IDW interpolation v surf idw input file vector data r surf idw input file raster data The IDW interpolation module for sites s surf idw of GRASS 5 4 is reshaped in v surf idw be c
105. hoice e GRASS 6 0 This GRASS version is the most recent GRASS version which is released early 2005 It is based on the development version 5 7 and includes all known raster functionalities of version 5 4 and the newly developed vector library The development of GRASS is continuing on the basis of GRASS 6 0 Therefor we like to encourage the users to use and test the version 6 0 this is necessary for further development The GDF Hannover bR only uses this version for its work GRASS 6 0 0 d m module GUIs Points sites as vectors 2D 3D vector support Vector network analysis DBMS support _Spatial Index Figure 6 Innovations between GRASS 5 4 and 6 0 The following descriptions are related to the installation on GNU Linux systems Thus they are accordingly modified transmissible on other platforms Each stables version will shortly be described GDF Hannover Courses 11 3 1 Installation of a binary version 3 1 Installation of a binary version GRASS versions 5 4 and 6 0 can be downloaded from the official GRASS GIS homepage 12 as binary versions Additionally GDF Hannover bR offers RPM packages for recent GNU Linux distribu tions 3 1 1 GRASS 5 4 Like mentioned before the GRASS Version 5 4 0 is officially released at the 5th of november 2004 In comparison to version 5 0 they include important further developments of raster functionalities The newly developed vector library
106. hors of the Document all of its principal authors if it has fewer than five unless they release you from this requirement 3 State on the Title page the name of the publisher of the Modified Version as the publisher 4 Preserve all the copyright notices of the Document 5 Add an appropriate copyright notice for your modifications adjacent to the other copyright no tices 6 Include immediately after the copyright notices a license notice giving the public permission to use the Modified Version under the terms of this License in the form shown in the Addendum below 7 Preserve in that license notice the full lists of Invariant Sections and required Cover Texts given in the Document s license notice 8 Include an unaltered copy of this License 9 Preserve the section Entitled History Preserve its Title and add to it an item stating at least the title year new authors and publisher of the Modified Version as given on the Title Page If GDF Hannover Courses 134 there is no section Entitled History in the Document create one stating the title year authors and publisher of the Document as given on its Title Page then add an item describing the Modified Version as stated in the previous sentence 10 Preserve the network location if any given in the Document for public access to a Transparent copy of the Document and likewise the network locations given in the Document for previous versions it was
107. hown as an example where a high threshold is chosen for demonstrating purposes The original map after the vectorization is displayed in red the map smoothed by the module v clean is overlain in blue It can be recognized that the number of vertices is reduced without destroying the topology of the map This can evoke a required visual effect and can also reduce the amount of data It is necessary to mention again that during a vectorization a change of geometries and also map information can occur Thus this modules must be handled with care Another possible procedure is to find the best threshold value with several attempts Converting sites During the reorganization of the vector architecture the sites format sites known in GRASS 5 4 has disappeared as own format Sites are now processed by the vector library The already intro duced module r to vect including the parameter feature point also vectorizes raster points 13 2 Converting vector data into the raster model For converting vector data areas lines and points into the raster model the module v to rast is available for this purpose During this process the parameters of the vector file which are supposed to be adopted in the raster map must be indicated GRASS Vectordata GRASS Rasterdata v to rast v to rast Figure 29 Modules for converting vector data into raster data according to 5 p The following options can be chosen attr gt
108. ht based licenses cannot and which isn t mentioned here as legitimate we will have to think about it and we will probably decide it is non free When talking about free software it is best to avoid using terms like give away or for free because those terms imply that the issue is about price not freedom Some common terms such as piracy embody opinions we hope you won t endorse See Confusing Words and Phrases that are Worth Avoiding for a discussion of these terms We also have a list of translations of free software into various languages Finally note that criteria such as those stated in this free software definition require careful thought for their interpretation To decide whether a specific software license qualifies as a free software license we judge it based on these criteria to determine whether it fits their spirit as well as the precise words If a license includes unconscionable restrictions we reject it even if we did not anticipate the issue in these criteria Sometimes a license requirement raises an issue that calls for extensive thought including discussions with a lawyer before we can decide if the requirement is acceptable When we reach a conclusion about a new issue we often update these criteria to make it easier to see why certain licenses do or don t qualify If you are interested in whether a specific license qualifies as a free software license see our list of licenses If the license yo
109. ht information i commands Command Description i cca Canonical components analysis cca program for image pro cessing i class i class i cluster An imagery function that generates spectral signatures for land i fft i fusion brovey i gensig i gensigset cover types in an image using a clustering algorithm The re sulting signature file is used as input for i maxlik to generate an unsupervised image classification Fast Fourier Transform FFT for image processing Brovey transform to merge multispectral and high res panchro matic channels Generates statistics for i maxlik from raster map layer Generate statistics for i smap from raster map layer Prosecution on next side GDF Hannover Courses 143 Prosecution Command description i group Creates and edits groups and subgroups of imagery files i his rgb Hue intensity saturation his to red green blue rgb raster map i ifft i image mosaic i maxlik i oif i ortho photo i pca i points i rectify i rgb his i smap i spectral i target i tasscap i vpoints i ZC color transformation function Inverse Fast Fourier Transform ifft for image processing Mosaics up to 4 images and extends colormap creates map mosaic An imagery function that classifies the cell spectral reflectances in imagery data based on the spectral signature information gen erated by either i cluster i class or i gensig Calculates Optimum Index
110. ierka 3D Precipitation Example Dataset Slovakia 2004 5 M Neteler GRASS Handbuch Der praktische Leitfaden zum Geographischen Information ssystem GRASS Geosynthesis 11 Geographisches Institut der Universitat Hannover 2000 6 M Neteler and H Mitasova Open Source GIS A GRASS GIS Approach Kluwer Academic Publishers Boston 2002 7 M Neteler and H Mitasova Open Source GIS A GRASS GIS Approach 2nd edition Kluwer Academic Publishers Springer Boston 2004 8 G Sherman T Sutton R Blazek and L Luthmann Quantum GIS User Manual Version 0 6 2004 Web References 9 GDF Hannover bR http www gdf hannover de 2005 10 Free Software Foundation Europe FSFE http www fsfeurope org 2005 11 GDAL Software Suite http www gdal org 2004 12 GRASS GIS http grass itc it 2005 13 Intevation GmbH http www intevation de 2005 14 GRASS Anwender Vereinigung Heimatseite http www grass verein de 2005 15 OGR Software Suite http www gdal org ogr 2004 16 FreeGIS Project http www freegis org 2005 17 FRIDA Projekt http frida intevation org 2005 18 pyshapelib bindings ftp intevation de users bh pyshapelib 2004 19 QGIS Development Team http www qgis org 2004 20 QGIS Wiki http wiki qgis org qgiswiki 2005 2
111. ilable line in 2 Delete line deletes an available line an additional click confirms the choice Edit attributes edits attributes of available elements Please consider One ele ment can represent several features Red button Exit digitizing module 18 3 2 Shapefile In comparison to the described GRASS plugin editing with shapefiles is different Due to the data format either point objects or line objects or polygone objects can be edited in one shape But it is possible to create new shapes The type of object must also be defined as point or line or polygone object This function can be found in the menu layer gt New vector layer In the following dialog window the vector type must be defined Processing the shapes can be started after entering the file name For this purpose the context menu of the appropriate layer offers two buttons for starting and stopping the process If a shape is in editing mode the symbol of the shape is signed with a little blue pen GDF Hannover Courses 123 18 4 GRASS Toolbox Vector Layer Zoom to extent of selected layer Toggle In Overview Remove Open attribute table Start editing Stop editing Properties Figure 46 Starting and stopping the editing process The editing functions of shapefiles are merely restricted on adding digitization The opulent range of functions of the GRASS plugin see Table 15 is not yet achieved for shapesfiles 18 4
112. in media that commonly have printed covers of the Document numbering more than 100 and the Document s license notice requires Cover Texts you must enclose the copies in covers that carry clearly and legibly all these Cover Texts Front Cover Texts on the front cover and Back Cover Texts on the back cover Both covers must also clearly and legibly identify you as the publisher of these copies The front cover must present the full title with all words of the title equally prominent and visible You may add other material on the covers in addition Copying with changes limited to the covers as long as they preserve the title of the Document and satisfy these conditions can be treated as verbatim copying in other respects If the required texts for either cover are too voluminous to fit legibly you should put the first ones listed as many as fit reasonably on the actual cover and continue the rest onto adjacent pages If you publish or distribute Opaque copies of the Document numbering more than 100 you must either include a machine readable Transparent copy along with each Opaque copy or state in or with each Opaque copy a computer network location from which the general network using public has access to download using public standard network protocols a complete Transparent copy of the Document free of added material If you use the latter option you must take reasonably prudent steps when you GDF Hannover Courses 133 begin di
113. in ogr If failure messages occur during import like it can be found in the polygone datasets FRIDA V1 0 1 try to correct these failures with the module v clean see chapter 11 5 Before starting to assign already available nodes within the roadnet to the individual hospitals it is necessary to create a new internal layer column It is thus possible to connect different attribute tables with the same vector map via layer allocations GDF Hannover Courses 86 12 2 Extracting hospitals from the point file Entry of a 2nd layer v category points out points_2f layer 2 op add Control v category points_2f layer 1 2 op print gt layer 1 layer 2 12 2 Extracting hospitals from the point file As next those points are extracted from the map points_2f that are assigned as hospitals in the region of Osnabrueck Extracting hospitals v extract in points_2f out hospitals_pre type point where poiTypName Klinik Hospital v select ainput points_2f binput hospitals_pre out hospitals Control v info hospitals gt one dblink v category hospitals layer 1 2 op print gt 2 layers d erase d vect roads d vect hospitals disp attr attr poiNameID bgcolor white bcolor black d vect hospitals col red icon basic diamond 12 3 Assigning hospitals to the roadnet In figure 25 the initial situation for calculating the optimal region borders is displayed For assigning the hospitals to the roads it
114. ings Name of new location newLocation Database ligat g rassdata Path to the EPSG codes file usr local share proj epsg browse EPSG code number of projection EPSG codes ok cancel u Figure 9 Screen for intergating an EPSG code C In some cases the data already contain all necessary projection information It is thus possible to generate a new Location during a running GRASS session using the projection information GDF Hannover Courses 17 4 1 Calling up a GRASS project contained in the data set to be imported For example a new Location can be created with a SHAPE file or a GeoTIFF file if a correct projection file prj is available unfortunately this is rarely the case Example Content of a SHAPE projection file prj PROJCS Transverse Mercator GEOGCS bessel DATUM Deutsches_Hauptdreiecksnetz SPHEROID bessel 6377397 155 299 1528128 TOWGS84 590 5 69 5 411 6 0 796 0 052 3 601 8 30 PRIMEM Greenwich 0 UNIT degree 0 0174532925199433 PROJECTION Transverse_Mercator PARAMETER latitude_of_origin 0O PARAMETER central_meridian 9 PARAMETER scale_factor 1 PARAMETER false_easting 3500000 PARAMETER false_northing 0 UNIT meter 1 Example Projection data of a raster map GeoTiff Driver GTiff GeoTIFF Size is 3570 3753 Coordinate System is PROJCS Transverse Mercator GEOGCS Deutsches_Hauptdreiecksnetz DATUM Deutsches_H
115. ist of all formats supported by OGR can be found in chapter 8 on page 34 as well as on the internet page of the OGR Software Suite 15 GDF Hannover Courses 63 10 2 Management of vector geometries ESRI SHAPE files can be used directly in GRASS For this purpose the new integrated module v external is used which makes the necessary connection between GRASS and the OGR source During this process a GRASS internal pseudo topology is automatically created for non topological data so that network analyses are also possible with this data Note that when using v external GRASS has read only access to the data which is slower than if the data are imported Create a SHAPE link v external dsn gdf shapes layer frida_stras out frida_stras_ext Display SHAPE d vect frida_stras_ext Query SHAPE d what vect frida_stras_ext In order to change the data the OGR data source must be imported into the native GRASS format g copy vect frida_stras_ext frida_stras_int v digit frida_stras_int This can be done by copying the already mounted map with the module g copy or by importing the dataset with the module v in ogr see chapter 5 2 Similarly all formats supported by OGR can directly accessed and or imported into GRASS Also PostGIS can be used to interface with the UMN mapserver So it is easy to present GRASS results through PostGIS and UMN mapserver on the internet 10 2 2 Creating geometries out of
116. istant Projection The distance between sites on the map remains undistorted on equidistant illustrations This is especially important for traffic maps 4 3 Examples of map projections Some examples of the different projection types and their characteristics are named in table 4 5 and 6 Further information concerning this topic can be found in 2 and 3 GDF Hannover Courses 22 4 3 Examples of map projections 4 3 1 Azimuthal Projections Table 4 Examples of azimuthal map projections Type Genomic Stereographic Orthographic Light source Vanishing point at the geocenter Vanishing point oppo site to the projection Vanishing point so far away that radiation center dips in parallel Properties true to scale where orthomorphic true to only true to scale in meridians and par scale where merid the projection center allels cross neither ians and parallels neither orthomorphic orthomorphic nor cross nor equal area equal area Application Circular regions In case of satellite im pages 4 3 2 Conic Projections Table 5 Examples of conic map projections maps of the middle latitudes Type Lambert Conformal Conic Albers Equal Area Conic Properties Orthomorphic Equal area Application For large scale and middle scale The parallels stand in pole proximity closer together than at the equator
117. it is issued p as edition If this map is supposed to be printed on a paper of DIN A4 a scale of 1 100000 is a possible variant The extent of the map on the paper of DIN A4 is 19 02 x 14 31 centimeter GDF Hannover Courses 113 17 4 Processing maps with Xfig 19 02 km 1902000 meter 100000 19 02 centimeter 14 31 km 1431000 meter 100000 14 31 centimeter Xfig offers the possibility of indicating a scale Thus it is easy to create an image frame including the necessary extent chosen scale by the drawing and editing features and to layout this image frame according to the own requirements see figure 37 nae Paint functions ae Edit functions SS S El 2 3 Include of pictures Rotate Rotate Figure 37 Range of interesting drawing and editing features in Xfig The export of the map from GRASS can be conducted with the PNG driver according to chapter 17 2 In order to get an optimal resolution of the raster map the variables GRASS_WIDTH and GRASS_HEIGHT of the PNG driver are supposed to be set according to the maps GDF Hannover Courses 114 17 4 Processing maps with Xfig Karte E metamorphic m transition E sandstone E limestone E sandy shale E claysand O no data C igneous Fer l b Figure 38 Simple map layout with Xfig at the example of the geological map from the Spearfish region GDF Hannover Courses 115 17 5 Proc
118. ith the command d rast For this purpose a GRASS monitor has to be started before with d mon x0 Starting the Display Manager d m amp GDF Hannover Courses 33 5 2 Importing vector data Displaying the map in the prompt d mon x0 d rast asterdem30m 5 2 Importing vector data In the latest version 6 0 GRASS the vector libraries underwent a complete reorganization This was necessary because the GRASS version 5 4 had a strong focus on raster data and sites analysis This course will focus on the new GRASS version 6 0 vector functions The changes to the vector format can be found in chapter 10 To import vector data it is essential to take a multitude of different format and standards into consid eration Compared to raster formats the structure of vector data is more complex This makes vector import more complicated Table 8 lists the formats which are supported by GRASS GIS Probably the most frequently used format is the ESRI SHAPE format Once the vector file is imported it will be available in the native GRASS binary vector format The geometries topologies and all attributes are stored in the internal GRASS database A topology is created for each map during the import The current topology status can be displayed via the command v info More vector related commands are described in chapter 10 Table 8 GRASS modules for importing vector data GRASS Import Module command Vector format
119. ithout sufficient knowledge and it should never be carried out manually outside of GRASS or with UNIX commands and or programs in Linux By using the command g mremove it is possible to delete several maps at the same time Exception The deletion of a complete mapset and location For this purpose GRASS has to be exit using the command exit The command rm r or a file manager e g konqueror can delete a mapset and or a location within the GRASS database Attention Accordingly all saved data maps files of the respective directories location mapset will be deleted For example The command rm rf grassdata Hanover irrevocably deletes without further en queries the complete location named Hanover with all its containing mapsets GDF Hannover Courses 31 5 Data import Before starting with the data import we should mention the model of the GRASS GIS data structure see chap 2 3 The terminology used in this section is explained in detail in the model Interoperability is an important condition for working with GIS for instance the import of raw data or data conversion from other software packages GRASS offers a large quantity of modules for importing vector data raster data and sites The specific command syntax can be displayed with the help parameter or the module g manual v in ogr help g manual v in ogr amp r in gdal help 5 1 Importing raster formats GRASS GIS supports the import of many differ
120. ition of the surface Sets all values on default In the following menus settings can be made concerning light conditions surface background color and further data Furthermore animated movies can interactively be created or programmed The help button is very productive in the graphical surface of NVIZ GDF Hannover Courses 104 16 2 Displaying raster volume layers VOXEL 16 2 Displaying raster volume layers VOXEL NVIZ displays also volume data besides raster surfaces Therefore the panel volumes is available It can be found at the menu Pane gt Volumes see figure 31 Volume Panel Current precip3d 500250 PERMANENT New Delete Visualization Type isosurfaces 4 Polygon Resolution Shading v 3 Position Isosurface Attribute _ toggle normal direction level 800 000000 N level 1000 000000 level 1300 000000 Delete Add Move Up Move Down Draw Current Close Figure 31 Volume panel for volume layer visualization Note This function requires an appropriate dataset with 3D options inside the actual mapset The GRASS module v in ascii offers a possibility to import 3D point data into the native 3D GRASS format using the switch z The button Add adds different levels of 3 dimensional layers to the display above the surface Color transparency shininess etc can be adjusted separately for each level using the button Ilsosurface Attribut
121. ity of a tower 15m over terrain computionally extensive at 10m original resolution r los in elevation 10m out visibility coord 593670 4926877 GDF Hannover Courses 53 9 3 Different raster applications GRASS PROGRAM profile PLOTTING PROFILE MAUSE Left DO ANOTHER BUTTON Middie CLEAR DISPLAY MNJ Right GUIT Ar From 591900 59 4920017 88 to 595248 12 4925717 69 1840 j B From 597638 44 4916114 78 to 582458 18 4917291 89 1340 Bi e C From 60B831 60 4925985 50 to 599830 75 4924726 42 1840 1066 D From B0B893 55 4916382 57 to 603486 08 4921195 02 1840 1066 Figure 16 Representation of different line transects of a relief model with d profile obs 15 max 30000 Control erase Shaded relief elevation 10m units meters rast elevation 10m_shade rast o roads a A A K QA rast o visibility 9 3 3 Overlapping of individual maps As already mentioned it is possible to overlay raster maps visually However the module r patch can be used to save the overlay as a new map Thus it is possible to combine several maps to a single map via patching o GDF Hannover Courses 4 9 3 Different raster applications r patch in map1 map2 map3 map4 out total map The first map indicated lies on top All other maps are successively placed under each other and only appear in those places where the maps lyi
122. ization and editing in QGIS In order to transmit all GRASS relevant variables to QGIS the program is supposed to be started out of a running GRASS session Figure 40 QGIS Screenshot including FRIDA dataset of Osnabrueck GDF Hannover Courses 117 18 1 Working with vector and raster data 18 1 Working with vector and raster data The advantage of QGIS is visualization of any data of any prevalent formats Thereby raster and vector data can be visualized to the same degree Like already described all raster formats including GRASS raster data can be loaded by GDAL Also large satellite image scenes can be visualized fluidly and quickly The continuously transparency is also a very good function which can be assigned to each raster layer Thus it is possible to display overlaying raster layer so that are shining through each other The context menu of the layer view contains the appropriate throttle for creating transparency Raster Layer Zoom to extent of selected layer Toggle In Overview Remove Transparency Properties Figure 41 Alpha Blending is supported by default QGIS also supports the creation of raster pyramids for a quick display of maps with different zoom stages For this purpose images with less resolution are created which are used by QGIS in depen dence of the already chosen zoom stage The whole range of functions of QGIS 0 7 is not only restricted t
123. l Thereby it needs to be considered that the pathes of additional programs and libraries must also be indicated when entering the command configure An example for keeping GDAL and PostgreSQL support could be the following configure with gdal usr local bin gdal config with postgres includes usr include pgsql usr include pgsql server with postgres libs usr lib make make install A detailed description of the configuration parameters offers the command configure help GDF Hannover Courses 13 3 3 Installation from CVS Examples of configurations can be downloaded from the Website of the GDF Hannover bR 9 under http www gdf hannover de download or from the GRASS Homepage 12 3 3 Installation from CVS Another variant is to download the source code of the GRASS versions 5 4 or 6 0 as a tarballed CVS snapshot from the GRASS Homepage 12 or directly from CVS For the latter the CVS needed environment variable CVSROOT has to be set Afterwards log into the CVS server which asks for a password and download the current source code on your computer and compile it like described in chapter 3 2 The following example shows this for a bash Shell export CVSROOT pserver grass guest intevation de home grass grassrepository cvs login PW is grass Now a copy of the source code can be downloaded with the following command cvs Z3 co grass
124. ld polylines Build polylines from lines v category Attach delete or report vector categories to map geometry v clean Toolset to clean vector topology v convert all v convert Imports older versions of GRASS vectors v db connect prints sets DB connection for a vector map v db select Print vector attributes v delaunay Create a Delaunay triangulation from an input vector of points or centroids v digit v distance Find the nearest element in vector to for elements in vector from Various information about this relation may be uploaded to the attribute table of input vector from or printed to stdout v external Create a new vector as a read only link to OGR layer Available drivers v extract Selects vector objects from an existing vector map and creates a new map containing only the selected objects If list file and where options are not specified all features of given type and layer are extracted categories are not changed in that case v hull Uses a GRASS vector points map to produce a convex hull vector map v in ascii Convert GRASS ascii file or points file to binary vector v in db Create new vector points from database table containing coor dinates Prosecution on next side GDF Hannover Courses 151 Prosecution Command description v in e00 Import of E00 file into a vector map v in garmin Upload Waypoints Routes and Tracks from a Garmin GPS re ceiver into a
125. levels above Slovakia 00 0550004 106 33 Creating a simple animationinNVIZ 0 eee ee es 107 34 Simple result map ps map Soil map with legend in the Spearfish region TERETE 110 35 Creating simple shading effects withd his o oo sooo 0000055 2s 112 36 __ Processing simple map layouts with Xfig pa a aa Sad Ee e G BH HU ee a ee ee A 113 37 Range of interesting drawing and editing features in Xfig ee ee ae ee ee e 114 38 Simple map layout with Xfig at the example of the geological map from the Spearfish TEJON 234 Hes a ee o wes a 2 ek a Sete eet ta aS eS 4a EE ae 115 GDF Hannover Courses vii List of Figures 39 Skencil with Geo Object Plugin at the example of the FRIDA dataset of Osnabrueck 116 40 _QGIS Screenshot ia ek ea ew Ee we 117 41 _Alpha Blending is supported by default 0 0 0 04 4 118 42 Dialog of the supported projections 0000 eee ee eee 119 43 Define your own projection 2 2 0 ee 120 44 Properties of the vector layer 2 ee es 121 45 QGlS in the editing mode of a GRASS vector map 122 46 Starting and stopping the editing process 2 0000005 124 47 _QGIS Toolbox aoo es 124 48 GIS GPS plugi lt s do tier e ee eh eee eee eae E a eE eas ea bas 125 49 Geospatial bookmarks a aoa a
126. line Q quit and create map In this way it is very simple to create masks but not necessarily precise GDF Hannover Courses 61 10 Restructuring vector features In GRASS Version 6 0 a complete revision of the vector features has taken place This contains a new vector format which removes the restrictions present in version 5 4 Thus a multitude of interesting innovations and changes are introduced at this point in the overview 10 1 New properties of GRASS 6 0 Vector geometries e Support of external simple feature data formats such as SHAPE or PostGIS without pre vious import at read only access via v external as virtual maps e Import into and export from GRASS to all OGR supported vector formats e New spatial index for reducing the computing time e g at v build for structuring the vector topology formerly v support in 5 4 Database Management e Attributes are stored in the DBMS SQL based interfaces to dBase files PostgreSQL MySQL and ODBC e Multi attributes are now internally saved in dBase files default or externally saved in DBMS e Multilayer features of a vector can be linked with one or more external database tables e 3D vectors can be created e g TINs CAD drawings and are also visually supported by NVIZ Modules e Support of SQL queries selections by for instance d vect v extract and v surf rst e Direct updating attributes is possible in the query e g attributes direct
127. ly linked with d what vect can be changed e Vector network analysis based on DGLIB Directed Graph Library e new digitalizing module v digit with GUI e export of SHAPE file DGN TIGER MapInfo and GML2 via the OGR library e user friendly module management with popup menus via the forms library e new GIS Manager d m In order to familiarize with the use of the new vector features the following chapters are mainly focused on the innovations of GRASS 6 0 especially the management of geometries and attributes GDF Hannover Courses 62 10 2 Management of vector geometries 10 2 Management of vector geometries The management of vector geometries has completely been changed in GRASS version 6 0 Ge ometries are stored in the new GRASS specific vector format native format as standard setting This basic setting can thus be modified without any problem so that at present PostGIS SHAPEs and other OGR supported formats can be saved and processed Geometrie Attribute Figure 18 Representation of the GRASS 6 0 vector architecture For a better comprehension for instance the use of the different currently supported vector formats will be introduced The Free Geodata of the FRIDA project are used for this purpose see 17 10 2 1 Working with OGR formats Due to the new implementation of the OGR support the support for a quantity of vector formats is now available A detailed l
128. n Name Click the button submit in order to update the new entry in the attribute table This is confirmed by the message Record successfully updated Once the digitization is complete exit the module v digit using the button Exit Thus the map forest is automatically saved and its topology is built Building topology 478 primitives registered 46 areas built isles built Topology was built Number Number Number Number Number Number Number Number of of of of of of of of nodes primitives points lines boundaries centroids areas isles 357 478 367 46 46 GDF Hannover Courses 84 12 Application example vector based optimization of operation areas A short training concerning the network module v net alloc is respresentatively introduced in this chapter for the new vector features Starting from defined points hospitals those regions are supposed to be determined which have to be achievable as quickly as possible for the respective first aid staff in an emergency situation Thus it is basically possible to assign different direction referred influencing factors speed road condition one way streets to the individual vectors and nodes roads and crossroads The application is restricted to an analysis by means of the distance that is to be travelled for this introducing example 12 1 Importing example data Like in some former examples the Free Geodata of the FRIDA pr
129. n and topographic analysis from given point or contour data in vector format to GRASS floating point raster format using regularized spline with tension v to db Load values from vector to database In uploaded printed cate gory values 1 is used for no category and null if category cannot be found or multiple categories were found v to points Create points along input lines v to rast Converts a binary GRASS vector map layer into a GRASS raster map layer v transform Transforms an vector map layer from one coordinate system into another coordinate system v type Change the type of geometry elements v univar Calculates univariate statistics for attribute Variance and stan dard deviation is calculated only for points v vol rst Interpolates point data to a G3D grid volume using regularized spline with tension RST algorithm v voronoi Create a Delaunay triangulation from an input vector of points or centroids Prosecution on next side GDF Hannover Courses 153 Prosecution Command description v what rast Upload raster values at positions of vector points to the table GDF Hannover Courses 154 Literature 1 R Bill and D Fritsch Grundlagen der Geo Informationssysteme Bd 1 Hardware Software und Daten Wichmann Karlsruhe 1991 2 G Hake and D Gr nreich Kartographie Berlin 1994 3 H Kamen Vermessungskunde Berlin 1986 4 H Mitasova and J Hof
130. nction of GIS is conducted by its own module Thus GRASS GIS is clearly structured and seems very transparent Another advantage of this modularity is that only the necessary modules are running which preserves the resources of the computer 2 1 Geographical Data GIS is characterized by four main components 1 e Input e Administration e Analysis e Presentation The discussed data types of this four component model are classified in three categories such as geometry data attribute data and graphics data with the following properties Geometry data describe the spatial situation of objects concerning their form and their relative situa tion in space Usually the spatial relation of individual points lines or areas is made via the integration in a coordinate system resulting in the relation to the real world and the metrics Geometry data can be available as raster data pixel or vector data polygons areas lines sites see Fig 2 Raster data are data continuously spread in space which are structured in a measured matrix of usually quadratic cells and cells with the same size Each cell gets an attribute property at tribute date which represents an appropriate phenomenon e g temperature or color value The storage of the cells is carried out by their coordinates They are adjusted in rows and columns The geometrical data are accessed via the geographical coordinates or by specifying the row and o
131. ndow where they can be selected using the mouse and subsequently edited The newly designed GRASS plugin in the geodata viewer QGIS 19 provides yet another means for changing GRASS vector file attributes A short description of this software package can be found in chapter 18 GDF Hannover Courses 69 11 Working with vector data The file structure for saving vector data differs between GRASS 5 4 and GRASS 6 0 as illustrated in figure 5 of chapter 2 3 For this reason old and new vector data can be created and managed in parallel in the same location mapset Furthermore file names can be maintained by converting data from GRASS 5 4 into the new native GRASS 6 0 format The module v convert converts old vector data out of GRASS 5 4 into the new native vector format v convert in grass5old_vector out grass60_vector g region p vect grass60_vector v info grass60_vector v db connect p grass60_vector d vect grass60_vector If necessary conversion from GRASS 6 0 format to the old vector format is possible via the ASCII format or the SHAPE format the latter process is recommended Note that the vector format of GRASS 5 4 can only save one attribute and one label each When using v in shape the attribute columns can be displayed by GRASS 5 4 with the parameter d EXPORTING VECTOR MAP FROM GRASS AS SHAPE v out ogr in grassnew_vector dsn layer vector_areas type area IMPORTING SHAPE INTO GR
132. ng above have the value NULL no data As an example the geological map and the roadmap from the Spearfish data set are to be overlayed It is important to consider that GRASS modules basically work in the current region and resolution Therefore the region with its resolution and area must be adjusted to the maps to be patched g region rast geology roads p res 12 5 a r patch in roads geology out roads on geol If the order of the maps is changed the entire roadmap is overlayed by the geological map Such an output map would ultimately be identical to the map geology 9 3 4 Buffering raster data The module r buffer allows the user to define a buffer based on the raster data This function can be used for creating noise protection zones for the individual road categories of the map roads Using the Spearfish data set first list the available categories Which road categories are available g region rast roads p r report h roads 1 interstate 2 primary highway hard surface 3 secondary highway hard surface 4 light duty road improved surface 5 unimproved road no data Problem To define buffer zones with distances of 100 250 and 500 meters around the interstate roads only The initial map has a resolution of 30 m which is maintained thoughout the exercise Extracting the category interstate with r reclass r reclass roads out interstate lt lt EOF 1 1 interstate EOF or extracting the categor
133. ntioned below such as Acknowledgements Dedica GDF Hannover Courses 132 m6 tions Endorsements or History To Preserve the Title of such a section when you modify the Document means that it remains a section Entitled XYZ according to this definition The Document may include Warranty Disclaimers next to the notice which states that this License applies to the Document These Warranty Disclaimers are considered to be included by reference in this License but only as regards disclaiming warranties any other implication that these Warranty Disclaimers may have is void and has no effect on the meaning of this License VERBATIM COPYING You may copy and distribute the Document in any medium either commercially or noncommercially provided that this License the copyright notices and the license notice saying this License applies to the Document are reproduced in all copies and that you add no other conditions whatsoever to those of this License You may not use technical measures to obstruct or control the reading or further copying of the copies you make or distribute However you may accept compensation in exchange for copies If you distribute a large enough number of copies you must also follow the conditions in section 20 You may also lend copies under the same conditions stated above and you may publicly display copies COPYING IN QUANTITY If you publish printed copies or copies
134. ntroid This centroid is thus inserted into the new digitized area see also feature Digitize new centroid Therefore you need to set the category mode to no category when Digitize new boundary and want to end up in areas Digitize new centroid is used in order to digitize a new centroid within a new area If an appropriate attribute table is available in the database it is automatically opened after the feature has been digitized Attrioutes are connected with areas via centroids Move vertex allows users to displace vertices Attributes can not be attached to vertices Also note that vertices are not nodes Vector points and centroids are never vertices and cannot be changed by this function The same applies for Add vertes and Remove vertex Add vertex allows users to add vertices Remove vertex allows users to delete vertices Split line makes it possible to interrupt a line at any position Here a new node is set for connecting additional lines as well as for attaching additional attributes Move point line boundary or centroid allows users to displace vector points vector lines and centroids If an area is disconnected by several nodes the total area is not displaced only the appropriate boundary Delete point line boundary or centroid allows users to delete vector points vector lines and centroids If an area is disconnected by several nodes the total area is not deleted only the appropriate boundary Zoom in
135. o no category The reason is that the area attributes are not supposed to be connected to the boundaries but to the centroids It is important to set the snapping threshold correctly so that lines are snapped together properly The default setting for the snapping threshold is 10 screen pixels but can be adapted to your own requirements using the button settings gt settings see figure 24 GDF Hannover Courses 83 11 6 Digitizing with GRASS _ settings Symbology Settings Table Background Snapping threshold in screen pixels f 0 snapping threshold in map units Ww fi 0 000000 Figure 24 Settings of the snapping threshold during digitization If a boundary has been digitized a centroid is supplemented to the area so that attributes can be connected with the area For this purpose click on the button digitize new centroid change the Mode from no category to Next not used and search on the monitor for an appropriate point within the newly created area in order to place the centroid If the centroid has been set with the left mouse button a graphical window is opened in which it is possible to assign additional attributes to the already set point according to the attribute columns defined before see figure 23 In this training only the category value is supposed to be supplemented by the landuse type Click into the window and enter the landuse type forest into the colum
136. o be explained see Figure 38 A detailed help is integrated in the program for a detailed description of the individual features Working with the program Xfig is easy to learn and besides numerous graphical features also some interesting properties are offered for creating map layouts Thus a scale can be indicated at the beginning which facilitates the drawing of map frames and captions see figure 36 GDF Hannover Courses 112 17 4 Processing maps with Xfig OUIETA Veaheraoentus Tenttscer tat tva enttas Teanttarovengard onntasdcnagetitrantttr esttea orsene anttardstente Temater eattteasemnetitveattiet tant tarTe iie EEA o x spearf ish_nap fig Legende E metamorphic oe m transition map area We 25 oO igneous ia ae Q 4 mai Scale ae jo Masta 1 100000 an eats Figure 36 Processing simple map layouts with Xfig Choosing the right scale Normally the procedure of creating a map layout starts with the consideration which scale the analog map is supposed to have This is mostly adopted to the paper format A4 A3 In the Spearfish region the extent of the location in east west direction is 19 02 km from the North to the South 14 31 km This can be found out for instance with the module g region g region d res 1 p The number of columns and rows of the total location d with a raster resolution of 1 res 1 in this case meter as un
137. o use a program means the freedom for any kind of person or organization to use it on any kind of computer system for any kind of overall job and without being required to communicate subsequently with the developer or any other specific entity The freedom to redistribute copies must include binary or executable forms of the program as well as source code for both modified and unmodified versions Distributing programs in runnable form is necessary for conveniently installable free operating systems It is ok if there is no way to produce a binary or executable form for a certain program since some languages don t support that feature but you must have the freedom to redistribute such forms should you find or develop a way to make them In order for the freedoms to make changes and to publish improved versions to be meaningful you must have access to the source code of the program Therefore accessibility of source code is a necessary condition for free software GDF Hannover Courses 128 In order for these freedoms to be real they must be irrevocable as long as you do nothing wrong if the developer of the software has the power to revoke the license without your doing anything to give cause the software is not free However certain kinds of rules about the manner of distributing free software are acceptable when they don t conflict with the central freedoms For example copyleft very simply stated is the rule that w
138. o visualize the current version also provides editing functions for vector data see chapter 18 3 It is also possible to change projections on the fly This means that data with different projections can be visualized in one target projection GDF Hannover Courses 118 18 1 Working with vector and raster data Generell Projection C Enable on the fly projection Projection Coordinate Systems Spatial Reference Id i Voirol 1879 2647 Voirol 1879 Paris 2667 WGS 72 2583 WGS 72BE 2584 mea WGS 84 2585 Xian 1980 2596 Yacare se ee ey QGIS SRSID 2585 PostGIS SRID 4326 proj longlat ellps WGS84 datum WGS84 no_defs i Figure 42 Dialog of the supported projections In figure 42 you can see the dialog box with the available projections If a needed projection is not yet predefined it is possible to define your own projection see fig 143 GDF Hannover Courses 119 18 2 Visualizing and categorizing Custom Projection Definition Name Projection Family e Parameters lt lt lt CIC reol gt oaae cese Figure 43 Define your own projection If the geodata do not contain any projection information QGIS automatically sets the view to a LatLong projection with WGS84 ellipsoid 18 2 Visualizing and categorizing Vector data can be provided with different displaying items on base of defined attributes For this
139. oject will be used here http frida intevation org These contain vector data of the city of Osnabrueck Germany Besides the current roadnet they also contain information concerning available waters and parks as well as interesting places hospitals schools etc The data format is ESRI SHAPE The creation of the necessary GauB Kruger location is automatically been carried out by importing the data into a new FRIDA location during a running GRASS session see also chapter 5 2 The import of the necessary SHAPE data is done by the module v in ogr e g in the Spearfish location STARTING ONE grass SESSION e g Spearfish dataset grass60 grassdata spearfish60 user1 IMPORTING ROADNET INCLUDING CREATION OF THE NEW LOCATION v in ogr dsn frida 1 0 1 shp joined strassen joined shp output strassen loc frida exit RESTART WITH NEW LOCATION grass60 grassdata frida PERMANENT IMPORTING SITES hospitals v in ogr dsn frida 1 0 1 shp joined poi joined shp output points GDF Hannover Courses 85 12 1 Importing example data 1a Ped E RR W sate PTT Ser res i Stk lt ES sav E RRO A A TOAN GA Uf a Ce EES BS COCO aA TB AR RX RL NN SY TP SKY BESS SA ora eee AS he ley apna S R fmm L A ee cH is Dirge NU ant 1 km HR A aeons HA SV BERR AFR ORT Figure 25 Basemap Roads and hospitals of Osnabrueck Topology problems are usually corrected during the import with v
140. ojection of a location can always be set on the previously defined default values via the module g region d While working with GRASS the module g region p lists the projection and resolution values currently being used 4 5 2 Creating a GauB Kriger project region The Gau Kr ger coordinate system uses a transverse mercator projection Accordingly the cylinder rotated 90 is transversely put over the Bessel ellipsoid Distortions occur in the border area max 12 cm km on a length of 2 This means the GauB Kriiger sheet sides are not displayed parallel to the sides of the paper in topographical maps using this projection Now the first task would be to choose the desired projection system from the menu However the GauB Kriiger system is not listed therefore we must select other These are the steps to be followed For the GauB Kriger system coordinate system for location other D GDF Hannover Courses 26 4 5 Creating different project regions in GRASS Followed by a short description of the project region one line description for location e g Hanover Further data of the projection are now following specify projection name tmerc Transverse Mercator specify ellipsoid name bessel Bessel Ellipsoid Do you want to specify a map datum for this location potsdam Enter Central Parallel lat_0 23N ON Enter Central Meridian lon 96W 9E Enter Scale Factor at the Central Meridian 1
141. ol point by double clicking on the point in the ANALYSE function window Points can be disconnected in this way to reduce the RMS error or to redistribute the points more evenly An even distribution of points with suboptimal RMS error can produce an overall lower error than a poor distribution of points with optimal RMS error The module i points is exited after the successful assignment of the control and reference points The coordinate assignments are automatically saved on exit This also applies to previously assigned points from prior executions of i points With a new call you can continue working on the same location Depending on the original data and the selected polynomial degree of the equalization to be per formed the module i rectify is started when sufficient points for georeferencing have been set In this context the group of images to be equalized must first be indicated The query follows whether the map 1 shall be transformed into the current region of the target location complies with the currently set parameters cutout resolution of the target location 2 or in the minimal region GRASS independently calculates the range in the target location If in this menu point 1 current region is chosen it is important to ascertain again before referencing that the current settings of the target location cutout and resolution are correctly chosen Due to the fact that all data are automaticall
142. on GDF Hannover Courses 25 4 5 Creating different project regions in GRASS 4 5 1 Examples Creating new project regions After starting GRASS see Chapter 4 1 click with the mouse on the button Create New Location for creating a new location Now the text based mode is opened see Fig 8 This is equivalent to starting GRASS with the setting grass60 text When a session is ended the start mode is saved and become the default start mode The start mode can be changed using the option grass60 gui or text Three entries must be made in the start window to define a new Location LOCATION The name of the project region to be created e g Hanover MAPSET The the name of a work area which is located within the Location e g Kronsberg DATABASE The full path to the GRASS database created using mkdir grassdata in which the project data have to be saved e g home user grassdata Please remember The mapset PERMANENT in which the general information of the project region is saved in individual files will automatically be created by GRASS see Chapter 2 3 even if you have entered an other name in the sector mapset Subsequently the keystrokes lt ESC gt lt ENTERs that is typical for GRASS leads you to the screen for defining the project region The creation of a GauB Kruger Location is described in chapter 4 5 2 The procedure for defining other coordinate systems is similar Advice The values for the pr
143. ons of the units used e g meter WIND Specifications of the current REGION and of the MAPSET pro jection VAR Specifications of the database driver and path 2 3 2 Design of further mapsets Each GRASS user can create one or several mapsets in which he administers his own project data They can have the extent of the whole project or smaller This characteristic of the GRASS database structure makes it possible to work with several users on one project at the same time e g in computer networks without running the risk of changing or destroying another user s data The mapsets of the other users can be specifically integrated in the users own project by granting read only permission The resulting maps of any analysis are saved in the mapset of the users current GRASS session GDF Hannover Courses 7 2 4 Command structure in GRASS Mapset file structure cats Category values e g color or temperature values and attributes classes with caption of the individual raster maps cell Individual raster maps cellhd Header rows of the individual raster maps cell_misc Statistical data of the individual raster maps colr Color information of the individual raster maps dbf Contains the internal vector attributes in DBASE format fcell Raster maps with floating point numbers f floating point hist Developing history of the individual raster maps vector Contains the individual vector data geometry topology etc
144. or During this process the module is controlled via the mouse and directly displays the result on the current vector map displayed on screen This module has only been designed for the entry of two points the start and end point If additional points are supposed to be used and or the resulting map is supposed to be saved the module v net path must be used v net path v net path works similarly to d path but needs more parameters Another difference is that it gener ates anew vector map containing the results Thus this module allows the user to save the generated pathes separately in vector datasets A possible application of this module is the calculation of the shortest paths based on a roadnet The free FRIDA dataset 17 of the city of Osnabrueck is available as a sample dataset The following command will find the shortest path between point 40 and point 71 echo 1 40 71 v net path mygraph out mypath For the use of driving directions the attribute columns forward and backwards can be included in the calculation GDF Hannover Courses 71 11 1 Network analysis The map mypath is created as the output map which contains the shortest path between the given points 11 1 2 Subnets within a vector network The module v net alloc can calculate subnetworks within a given vector network For example this can be used to to calculate the scope of several police stations within a city This kind of in
145. p for using GRASS modules 2 2 2 0 000 eee ee 9 2 6 GRASS Vallables 2 32 34 22344 45 4 6464045466 64823 59444 5 4 E6844 9 3 Installation of GRASS 11 3 1 Installation of a binary version oaoa a 12 Ot GRASS OA yeee be OR e e S a Se oO ee ee ee eee 12 3 1 2 GRASS 6023 ee ee sprr aa eed dba SSR GS EADS ERM EASES SS 12 3 2 _ Installation from source code 2 ec we ee ee ee 13 3 3 Installation from CVS es oak ee OR OY Oe ARSE w OSS EL RS AS amp Ered 14 4 GRASS Project database 15 4 1 Calling up a GRASS project 2 2 2 2 ee 15 4 2 Projecti rns s srog a si Ble poni Gok A eth BAR Ee SHI Bee O98 Bod bw BoE 19 4 2 1 GSO s sx fa Ek SS SEK SSS EER Ge AER Yee OOM YES amp Eres 19 42 2 EPSON gost ecards eh Be Sek Bk Se ee ee ee ee es Se Se 19 4 2 3 DaM re redeas he ee hee eGo eRe edad eA 20 4 24 Map projection types 2 wd ke ee ee eRe ee ee EE 20 4 2 5 Choosing the projectiontype 2 a ee ee 22 4 3 Examples of map projections 2 2 2 00 ee ee ee 22 4 3 1 Azimuthal Projections 5 202 62 ae ea we we Reid ee ee eS 23 4 3 2 Conic Projections ooa e re6 Raw SE eGR E DEL EA 23 4 3 3 Cylindric Projections oie Pe ke AR ae Bee OE Ee Se eS 23 4 4 Coordinate systems 2 ee ee 24 4 4 1 Global coordinate systems ooo ee 24 4 4 2 2and3 dimensional coordinate systems 44 24 4 5 Creating different project regions in GRASS aooo 25 4 5 1 Examples Creating ne
146. plugin offers a convenient GUI for digitizing vector data Therefore all features of the GRASS module v digit are supported Attributing new vector structures as well as attributing vector structures that are already available in the file is also possible QGIS was born in May of 2002 and since then in steady development Therefore it is possible that some functions do not yet work as espected Nevertheless QGIS already offers some interesting features like simple reading out of GPS devices georeferencing of raster maps QGIS plays an important role for GRASS concerning the GUI devel opment and this program should therefore be kept in mind At present the functions of table 15 for digitizing with the GRASS plugin are available GDF Hannover Courses 122 18 3 Editing Table 15 GRASS digitization tools according to 8 a Tool Aim New point digitizes new point New line digitizes new line choose new tool for exit New boundary digitizes new boundary choose new tool for exit New centroid digitizes new centroid label available surfaces Move node selects an existing node on a line and displaces this node to a new position New node adds a new node to an existing line Delete node Deletes a node of an existing line an additional click confirms the choice Displace line selects an existing line and displaces this line to a new position Divide line divides an ava
147. po the header information head the vector geometries coor the history hist the spacial index sidx and the category index cidx as well as a link to the corresponding attribute data dbIn are stored According to the default the attribute data has been stored within GRASS in the directory dbf as DBASE format also during the import If required it is possible to have a look at the content of the newly imported attribute table streets dbf with an appropriate editor Under GNU Linux this can be done with OpenOffice Gnumeric or Koffice Other methods for importing vector data or generating vector data based on databases such as PostgreSQL or PostGIS can be found in chapter 10 If the vector data contain their own projection information a new location can be created during a GRASS session which is based on this information The necessary information of SHAPE data are saved in the file with the ending prj Creating a new location with the import of the data has the following syntax v in ogr dsn frida 1 1 shp joined streets joined shp out streets location osnabrueck 5 3 Importing sites In GRASS 6 0 sites are no longer stored seperately in a directory site_lists but they are saved as vector points and analysed with the vector modules Vector sites that are for instance available as SHAPE data will be imported with the module v in ogr like it is mentioned in the following example GDF Hannover Courses 35 5 3 Impo
148. r than needed so when in doubt it is possible to play it safe and define a generous location storage space does not cost extra The resolution is set to 1 so that each pixel of original image can be assigned to a raster field in GRASS Usually the geographical resolution e g in meters determines the number of pixel of the scanned map However this connection is irrelevant in the projection free XY location Only later with the transformation to another coordinate system will the genuine resolution specified by the scan resolution and the map scale be assigned The second step is to create a target location into which the georeferenced map is to be transformed The target location will provide the projection extent and resolution required by the project In the simplest case a target location already exists to which the georeferenced map will be added The creation of a target location is described in chapter 4 5 1 Procedure for several map segments Ifa map consists of several segments each segment should be imported independently into separate XY locations in order to exclude slips of the pen during the georeferencing Otherwise the map can be composed with an image editing program before importing into GRASS in order to import the map as a whole but only if the scans are properly cut This is only recommended if the data to be imported already lie properly one upon the other as image data An example could be unreferenced
149. r column Working with raster data allows the application and analysis of remote sensing data such as color infrared images of aerial operations satellite photographs images and more The necessary memory requirements and the appropriate high demand on comput ing resources cpu time which rise exponentially with the increase of resolution is to be seen as a disadvantage of raster data Due to steady increasing CPU power and larger storage capacities this disadvantage has become less important over the last few years Additionally raster data are not associated with so called neighborhood relationships because each pixel is defined by its own situation in the coordinate system GDF Hannover Courses 2 2 1 Geographical Data Rasterdata Vectordata 10 23 23 35 35 44 67 88 88 y 52 4 25 18 5 y X X Pointdata attribute data x 3595555 5774906 Lts y i x R y 3595249 5774455 Lts A o 3595009 5774123 Ls x 3595867 5774983 Su j xX X 3595339 5774445 Ls 3595889 5774101 Lts X Figure 2 Geometry and attribute data within Geographical Information Systems Vector data are used for the storage of line information and or for the storage of homogeneous areas at closed lines polygons One line connects two end points nodes each which also have coordinates Each vector object can be assigned wit
150. rder to guarantee a passably fluent animation there should be at least 100 images Now the starting position of the animation is defined By clicking on the button Ada this first position is saved Afterwards a new position is selected on the timeline Key Frames and the map is displaced to a new position within the control window see figure 30 The second setting is also be saved with the button Ada This procedure is repeated until the timeline is full If all settings are defined and tested the result can be saved with the button Run and Save The images saved in a separate folder can now be combined to a GIF animation or an mpeg movie via external programs 6 GDF Hannover Courses 107 17 Visualizing and creating maps ready for press An important component for working with spacial data is their visualization and presentation no matter as analog 2D paper map digital 3D model or as a picture animation The requirements a contem plator claims to GIS often correspond to the experiences from professional graphic software and are accordingly set high In this sector GRASS offers two different possibilities On the one hand there is the module ps map in order to create simple map layouts in the postscript format On the other hand the possibility of exporting result maps into different image formats is offered These image formats can thus be processed with external professional graphic softwa
151. re 17 1 Map export into a postscript map ps map offers a possibility to create hardcopy concept maps The result is a postscript map which might be enough for getting an overview The interactive query can optionally be saved as a textfile This offers the advantage of modifying the layout without running through the complete interactive query for several times The textfile of figure 34 will be as follows and was copied from the helpfile see g manual ps map raster soils outline color black width 1 end comments soil cmt where 1 6 font Helvetica end colortable y where 1 6 5 cols 4 width 4 font Helvetica end setcolor 6 8 9 white setcolor 10 green vlines roads width 2 style 0111 color grey GDF Hannover Courses 108 17 1 Map export into a postscript map masked n end vlegend where 4 5 0 font Courier fontsize 8 end text 30 100 SPEARFISH SOILS MAP color red width 1 hcolor black hwidth 1 background white border red size 500 ref lower left end line 606969 73 3423092 91 616969 73 3423092 91 color yellow width 2 end point 40 60 color purple symbol basic diamond size 25 masked n end scale 1 125000 scalebar f where 4 5 6 5 length 5000 height 0 05 segment 5 numbers 5 end geogrid 60 s color blue numbers 2 yellow end paper a4 end end GDF Hannover Courses 109 Map export into a postscript map 17 1 mds CPERMGNEUTS GDF Hannover tooo aaggei3222a
152. reas built O isles built Topology was built Number of nodes 203 GDF Hannover Courses 82 11 6 Digitizing with GRASS Number Number Number Number Number Number Number of of of of of of of primitives points lines boundaries centroids areas isles Forest areas east of Spearfish Finally the forest area surrounding the landmark is to be digitized Also in this case the module v digit is started and a new map forest is automatically created by the option n The imported topological map tk24 is loaded as background map Start the digitizing module and create new blank map g region rast tk24 d mon x0 v digit n map forest bgcmd d rast tk24 The GUI of the module v digit see figure 20 is automatically started again and the TK24 is loaded in the GRASS monitor x0 as background map A new attribute table including an extra column Name is now newly created in the v digit GUI via the button settings gt Table see figure 22 Then zoom into the region east of Spearfish see figure 21 and start to digitize the forest areas by clicking on the button digitize new boundary and by searching an initial range on the monitor for the digitization The assignment of the mouse buttons can be found in the GUI Here it is also possible to determine the layer entry and the kind of the allocation of the category values For digitizing the forest areas change the mode from Next not used t
153. rical connection with the subject or with related matters or of legal commercial philosophical ethical or political position regarding them The Invariant Sections are certain Secondary Sections whose titles are designated as being those of Invariant Sections in the notice that says that the Document is released under this License If a section does not fit the above definition of Secondary then it is not allowed to be designated as Invariant The Document may contain zero Invariant Sections If the Document does not identify any Invariant Sections then there are none The Cover Texts are certain short passages of text that are listed as Front Cover Texts or Back Cover Texts in the notice that says that the Document is released under this License A Front Cover Text may be at most 5 words and a Back Cover Text may be at most 25 words A Transparent copy of the Document means a machine readable copy represented in a format whose specification is available to the general public that is suitable for revising the document straightforwardly with generic text editors or for images composed of pixels generic paint programs or for drawings some widely available drawing editor and that is suitable for input to text formatters or for automatic translation to a variety of formats suitable for input to text formatters A copy made in an otherwise Transparent file format whose markup or absence of markup has been arranged to thwa
154. rt or discourage subsequent modification by readers is not Transparent An image format is not Transparent if used for any substantial amount of text A copy that is not Transparent is called Opaque Examples of suitable formats for Transparent copies include plain ASCII without markup Texinfo input format IATEX input format SGML or XML using a publicly available DTD and standard conforming simple HTML PostScript or PDF designed for human modification Examples of transparent image formats include PNG XCF and JPG Opaque formats include proprietary formats that can be read and edited only by proprietary word processors SGML or XML for which the DTD and or processing tools are not generally available and the machine generated HTML PostScript or PDF produced by some word processors for output purposes only The Title Page means for a printed book the title page itself plus such following pages as are needed to hold legibly the material this License requires to appear in the title page For works in formats which do not have any title page as such Title Page means the text near the most prominent appearance of the work s title preceding the beginning of the body of the text A section Entitled XYZ means a named subunit of the Document whose title either is precisely XYZ or contains XYZ in parentheses following text that translates XYZ in another language Here yb XYZ stands for a specific section name me
155. rting sites v in ogr o dsn frida 1 1 shp joined poi joined shp out poi 268 primitives registered O areas built O isles built Number of nodes 268 Number of primitives 268 Number of points 268 Number of lines Number of boundaries Number of centroids Number of areas O G O GOG O Number of isles Importing Eastings and Northings X Y Often sites are given as eastings and northings in simple ASCII table to be imorted into GIS For this purpose GRASS offers the module v in ascii The sites should be listed in the order Easting Northing Value The separator plays no special role For example a file coord txt shall be imported whose columns are separated by the pipe sign 1664619 5103481 1664473 5095782 1664273 5101919 cat coords txt v in ascii out points Missing category values IDs can be added after the fact using the v category module so that it is possible to assign additional attributes to be stored in the database v category in punkte out points2 op add v category points2 op report The site information is then available as GRASS vector format in the current location in the folder vector of the GRASS database Importing elevation data X Y Z If a third column contains elevation data as the attribute the parameter z must be added to the v in ascii command 1664619 5103481 101 2 GDF Hannover Courses 36 5 3 Importing sites 1664473 5095782 102 2 1664273 5101919 1
156. s can apply the knowledge acquired through the exercises and examples to daily use even after finishing the course The content of this book is based on the GDF Hannover bR course titled An introduction in the practical use with the Free Geographical Information System GRASS 6 0 This book is mostly based on the longtime experiences of our internal and external employees of being used as teaching material at the University of Hanover and of the cooperation in the GRASS Development Team Corresponding to our company philosophy we always endeavor an active contri bution for promoting distributing and advancing Free GIS Software For this reason all chapters of this book are published according to the GNU Free Document License and are available on the GDF Hannover bR 9 website The topics of our beginners courses are chosen depending on the respective duration as well as on the specific ambitions of the participants The individual chapters are therefore designed to provide an overview of the basic functions of the GRASS system and do not refer to any specific examples or contents of GRASS courses of the GDF Hannover bR This book is meant to be a compact and clear introduction to GRASS 6 0 and quickly inform the reader about the basic functions of the program For more insight in the software see the appropriate book titles of the respective topics indicated in the bibliography GDF Hannover Solutions for spatial data analysis an
157. s of the GRASS GIS Homepage 12 3 1 2 GRASS 6 0 The install procedure is identical to GRASS 5 4 and will be mentioned here see chapter 3 1 1 GDF Hannover Courses 12 3 2 Installation from source code Again the program and the appropriate installation script need to be downloaded into an arbitrary directory before installing the version with root permissions su RK sh grass6 0 0_i686 pc linux gnu_bin tar gz grass6 0 0_1686 pc linux gnu_bin tar gz If the requirements differ from these requirements it is necessary to compile the present source code of the version GRASS 6 0 0 on your own computer This procedure can be useful because the binary version mostly does not include all features and modules e g external database support After a successful installation GRASS 6 0 can be started from the command line by typing grass60 3 2 Installation from source code For the case that it is necessary to compile the source code of the GRASS versions 5 4 or 6 0 on your own computer we shortly want to explain this procedure with an example It should be taken into account that this requires a little experience in compiling as well as studying of the installation helps for installing GRASS without any problems in the required version The compiling and the installation is conducted with the rule of proportion which is common for Unix after the downloaded source code is unpacked configure make make instal
158. s the steps involved in deriving a map projection from real spatial data i y I i Xx ee Projection to Area with Ellipsoid to plain area coordinates Figure 10 Projection of the earth s surface on a map according to 7 4 2 1 Geoid A more precise definition of the earth s shape especially of the heights can be made via the identi fication of the geoid This considerably more complex physical calculation results from the quantity of the earth masses which occur differently strong from region to region and therefore have different gravitation forces which affect on the earth s shape Thus the geoid represents the gravitation field of the earth In case of the view in Figure 10 the shape of the earth looks really distorted Due to the mathematical complexity the earth s shape is usually displayed by ellipsoids in Geographic Information Systems 4 2 2 Ellipsoid The simplified acceptance of the earth in spherical shape sphere is not exactly enough for creating maps in higher scales than 1 2 Mio Rotation ellipsoids or else spheroids try to readjust the complex form of the earth mathematically as exactly as possible Thereby the distance between the poles GDF Hannover Courses 19 4 2 Projections and the geocenter is smaller than between the equator and the geocenter see Fig 10 There is a range of ellipsoid models existing that should give optimi
159. satellite images which have been supplied congruently for different spectral ranges GDF Hannover Courses 39 6 2 Georeferencing procedure 6 2 Georeferencing procedure Once the XY location with the raw map and the target location with the projection have been created we are ready to georeference the raw map as follows 1 Indicate the name of the map and image data that are to be transformed into a newly created image group i group e Assign names for this group e g map e Select the map s to be imported with an x 2 Indicate the target location target and mapset e g a GauB Kruger location in which the map and image data shall be transferred i target e The target location should not be zoomed Otherwise the end product is only transferred to the zoomed cutout because GRASS always works with the current region Reset the standard resolution in the target location as follows g region dp 3 Start a GRASS monitor d mon start x0 4 Assign the GauB Kriger coordinates to the four edges or coordinate crosses of the region to be transformed see chapter 6 2 1 i points Related to raster maps i vpoints Related to vector maps e Indicate the image group to be transformed for this example map 6 2 1 Choosing control points The imported map image is clickably displayed in the GRASS monitor on the left hand side There are two possibilities for georeferencing either A using reference coordinat
160. stribution of Opaque copies in quantity to ensure that this Transparent copy will remain thus accessible at the stated location until at least one year after the last time you distribute an Opaque copy directly or through your agents or retailers of that edition to the public It is requested but not required that you contact the authors of the Document well before redistribut ing any large number of copies to give them a chance to provide you with an updated version of the Document MODIFICATIONS You may copy and distribute a Modified Version of the Document under the conditions of sections 20 and 20 above provided that you release the Modified Version under precisely this License with the Modified Version filling the role of the Document thus licensing distribution and modification of the Modified Version to whoever possesses a copy of it In addition you must do these things in the Modified Version 1 Use in the Title Page and on the covers if any a title distinct from that of the Document and from those of previous versions which should if there were any be listed in the History section of the Document You may use the same title as a previous version if the original publisher of that version gives permission 2 List on the Title Page as authors one or more persons or entities responsible for authorship of the modifications in the Modified Version together with at least five of the principal aut
161. sun position and DEM Either A exact sun position is specified or B date time to calculate the sun position by r sunmask itself Surface area estimation for rasters Surface generation program from rasterized contours GRASS module to create a fractal surface of a given fractal di mension Uses spectral synthesis method Can create interme diate layers showing the build up of different spectral coefficients see Saupe pp 106 107 for an example of this Use this module to generate naturally looking synthetical elevation models DEM Prosecution on next side GDF Hannover Courses 149 Prosecution Command description r surf gauss GRASS module to produce a raster map layer of gaussian devi ates whose mean and standard deviation can be expressed by the user It uses a gaussian random number generator r surf idw Surface interpolation utility for raster map layers r surf random r terraflow r texture r thin r timestamp r to vect r topidx r topmodel r transect r univar r univar sh r water outlet r watershed r what Produces a raster map layer of uniform random deviates whose range can be expressed by the user Flow computation for massive grids Float version Generate images with textural features from a raster map Thins non zero cells that denote linear features in a raster map layer Print add remove a timestamp for a raster map Converts a raster map into a vector map layer Creates topo
162. surface GDF Hannover Courses 59 9 6 Methods for manipulating rastermaps 4 light duty road improved surface 5 unimproved road x no data RECLASSIFICATION r reclass in roads out roads rcl Enter rule s end when done help if you need it Data range is 1 to 5 gt 12 3 1 good condition gt 4 5 2 bad condition gt end CLASSIFICATION AFTER r report roads rcl 1 good condition 2 bad condition no data The module r mapcalc offers the possibility of creating an independent map again g region rast roads rcl p r mapcalc newmap roads rcl 9 6 2 Masking The masking of image ranges can be very helpful in the forefront of raster operations Masks that are set influence all successive raster analyses just like the currently set region or resolution Basically only a map with the name MASK in upper case is considered as mask in the respective mapset by the raster modules For this map no analysis will be made for areas where the pixel value NoData NULL is assigned in the MASK All other areas are used during the calculation A mask can be created in many different ways If an appropriate map is already available it can simply be copied or renamed g copy rast Mask MASK g rename rast Mask MASK The module r mapcalc offers an other possibility For a potential mask it allows the extraction of pixel values which have to operate as a mask see chapter 15 GDF Hannover Courses 6
163. t anymore but shows a diminution factor of 0 9996 At Gau B Kr ger the northing is measured in kilometer as the distance of the point from the equator On the contrary 10000 km are added on the southern hemisphere in order to avoid negative values The distance from the central meridian which has the values 500km like at GauB Kriger is defined by the x values The appropriate coordinates are indicated with E East and N North The central meridians can be found at 3 9 15 and so on in eastern and or western longitude The zones are divided into 8 latitude stripes from the South pole to the North Pole and they are indicated with letters This system is used for military maps of the United States and of the NATO According to the international usability of the UTM coordinate system also Germany and or Europe endeavor the introduction of this coordinate system 4 5 Creating different project regions in GRASS After this excursion though the world of projections which play an important role for working with geographical information systems it is time to introduce the process of defining project regions Lo cations in GRASS see Chapter 4 1 To create a Location the following parameters must be known 1 Coordinate system xy environment or environment with projection ellipsoid and datum 2 Area of interest minimum and maximum coordinates of the work area 3 Raster resolution usually the most frequently occurring raster resoluti
164. t is absolutely important to note that during the deletion of the vectormap all attribute tables which are indicated in the dbin and therefore linked with this map are deleted In order to avoid this it one can make a copy of the respective attribute table and link the copy to the vectormap instead of the original db copy from_driver dbf from_table origtable to_driver dbf to_table copytable For changing the current settings of a database the following commands are available e DBF driver dbf database GISDBASE LOCATION_NAME MAPSET dbf GDF Hannover Courses 66 10 3 Managing vector attributes e ODBC driver odbc database grass60test e PostgreSQL driver pg database host pgserver itc it dbname grass60test user name e mySQL driver mysql database grass60test The db modules are completely independent from the v modules in GRASS and do only allow the modification of attribute tables The dbf format is used as default This can be set with the following command db connect driver dbf database GISDBASE LOCATION_NAME MAPSET dbf User password management with external databases For attribute data storage in external databases like PostgreSQL user management is also possible The module db login takes control about a database and store its information in HOME grasslogin6 So working in groups is possible A possible scenario can be as follows Location gt database Mapset
165. ted here can additionally be varied by the situation of the illustration plane to the earth Normal 0 to the axis of the earth oblique 45 to the axis of the earth or diagonal axial 90 to the axis of the earth GDF Hannover Courses 21 4 3 Examples of map projections 4 2 5 Choosing the projection type The decision for a projection depends on the illustration properties needed in the project Despite the fact that a map projection is generally never displayable without distortions of one or several characteristics area form distance scale direction or relation it must be specified before which properties have priority at the planned usage of the geodata Orthomorphic Projection The scale remains the same from one point in all directions The merid ians and parallels intersect by 90 The scale is locally the same and thus the form of the areas remain Additionally the angles between the lines remain unchanged These maps are mainly used in the navigation and the surveying technology Equal area Projection Here the area dimensions remain scaled as well as the proportional re lations of the areas also remain Scale form and angle are distorted The meridians do not intersect the parallels in the right angle But this is not very important concerning smaller areas These projections are often used for land use mapping and population mapping as well as for other researches that are related to one specific area Equid
166. th legend A rastermap with appropriate legend can be displayed quickly by entering the following command d rast leg rastermap 9 2 Query of raster cell values and metadata In order to get coordinates and raster attributes of individual pixels the module d what rast can be run after displaying the raster map d what rast It is also possible to query multiple rastermaps that have not been displayed d what rast map elevation dem geology soils By clicking on a pixel with the mouse its characteristic values are displayed in the terminal window Also the attribute values of a pixel can be queried in several maps displayed in the monitor Exit the module by clicking the right mouse button r info The r info module is used for displaying basic information and metadata information for the rastermap It also shows a data description data type the map projection and the value ranges of available categories r info landuse r info r landuse r cats To control the attributes of a rastermap create a table with assigned label numbers and appropriate text attributes using the r cats module cats map landuse residential commercial and services f 1 2 3 industrial 4 other urban 5 reservoirs GDF Hannover Courses 51 9 2 Query of raster cell values and metadata 6 bare exposed rock 7 quarries strip mines and gravel pits 8 transportation and utilities r report To determine the area of individual geological units in
167. the Spearfish region for example use the r report module as shown below also see r stats This module calculates statistics based on the current region and raster resolution settings Therefore zooming in prior to executing this command will describe the cutout region only g region rast geology p r report h geology units h 1 metamorphic 1051 000 2 transition 13 000 3 igneous 3285 000 4 sandstone wo Gh Se te Be Ae ah oh A ee Ae ae fas Se tl 9675550007 5 limestone ee ee ee ee ee ee ee 655 37 0001 6 shale 4170 000 7 sandy shale 1019 000 8lclaysand 1307 000 9lsand 3295 000 no data on 168 000 asete a e a TOTAL 26 600 000 poo r timestamp For processing time series it is often necessary to provide maps with a timestamp time of creation data acquisition and so on For this purpose the module r timestamp is used Absolute and relative dates can be indicated which are stored independently from the file history r timestamp landuse date 27 Sep 2003 r timestamp landuse date 27 Sep 2003 20 Feb 2004 GDF Hannover Courses 52 9 3 Different raster applications A more detailed description of the available timestamp formats can be found in the help file via g manual r timestamp 9 3 Different raster applications GRASS is very extensive especially with regards to raster
168. the category values from multiple raster map layers r describe Prints terse list of category values found in a raster map layer r digit r digit r distance Locates the closest points between objects in two raster maps r drain Traces a flow through an elevation model on a raster map layer r fill dir Filters and generates a depressionless elevation map and a flow direction map from a given elevation layer r fillnulls Fills no data areas in raster maps using v surf rst splines interpo lation r flow Construction of slope curves flowlines flowpath lengths and flowline densities upslope areas from a raster digital elevation model DEM r grow Generates a raster map layerwith contiguous areas grown by one cell r his Generates red green and blue raster map layers combining hue intensity and saturation his values from user specified input raster map layers r in arc Convert an ESRI ARC INFO ascii raster file GRID into a binary raster map layer r in ascii Convert an ASCII raster text file into a binary raster map layer r in bin Import a binary raster file into a GRASS raster map layer r in gdal Import GDAL supported raster file into a binary raster map layer r in gridato Imports GRIDATB FOR map file TOPMODEL into GRASS raster map r in mat Import a binary MAT File v4 to a GRASS raster r in poly Create raster maps from ascii polygon line data files in the current directory r in srtm Import SRTM90 HGT files into G
169. the dataset there will be data loss and the resulting GIS will be less than satisfactory Therefore it is useful to choose the standard resoultion default to be equal to the resolution of the most important data layers The raster resolution can always be adjusted once the region has been created When importing data the original resolution and map size is preserved Now that the properties of the project region and the data resolution have been determined the next step is to create a subdirectory for the GRASS database This is usually called grassdata see chapter 2 3 4 1 Calling up a GRASS project If the start script of the version GRASS 6 0 is in the path PATH GRASS can be started within an open command interpreter X Terminal via the command grass60 A more detailed description can be found in chapter 3 The resulting start screen is shown in which some data must be entered via mouse or keyboard A graphical or text based variant can be chosen by setting the parameter text or gui when starting GRASS see Fig 8 and 7 grass60 text text based start screen grass60 gui graphical start screen GDF Hannover Courses 15 4 1 Calling up a GRASS project 6 0 cvs Data Selection Welcome to GRASS GIS Version 6 0 cvs Please select location and mapset or define a new location Database home neteler grassdata Browse a Location Accessible Mapsets Create new mapset
170. the name of the viewpoint Click with the mouse in the window and enter Lookout Peak in the column Name and then click on the button submit in order to add the new entry to the attribute table This is confirmed by the message Record successfully updated Now cloes the v digit module by clicking on the Exit button Thus the created map lookout is automatically saved and its topology is built Building topology GDF Hannover Courses 80 11 6 Digitizing with GRASS 1 primitives registered O areas built o O isles built Topology was built Number of nodes Number of primitives Number of points Number of lines Number of boundaries Number of centroids Number of areas O O O OO FF Fe Number of isles Digitizing contour lines The next exercise is to digitize the 100m contour lines situated around the point of interest As in the previous example the module v digit is started again and a new map contour_lines is automat ically created by the option n The imported topographical map tk24 is loaded as the background map Start the digitizing module and create new blank map d mon x0 g region rast tk24 v digit n map contour_lines bgcmd d rast tk24 The graphical user interface GUI of the module v digit see figure 20 is automatically started and the TK24 is loaded into the GRASS monitor x0 as the background map Now create a new attribute table including an extra column height in the v digit GUI
171. tion The module v extract extracts vector geometries and attributes from a map and saves them as a new map In the following example the political border of the Federal State Lower Saxony is extracted from the map pol_borders v extract in pol_borders out pol_borders_nds type area new 1 where nam NIEDERSACHSEN GDF Hannover Courses 74 11 4 Data selection 11 4 Data selection The map roads contains the most important roads throughout Germany The roads of the Federal State of Lower Saxony are only supposed to be interesting for a project In order to extract them those road vectors are selected from the map roads based on the political borders of Lower Saxony map pol_borders_nds which lead throughout the Federal State of Lower Saxony For this purpose use the module v select v select ain roads bin pol_borders_nds out nds_roads 11 5 Topology management For creating analyzing and repairing topology of vector data the modules v build as well as v clean are available v build The module v build is the successor to the module v support known from GRASS 5 4 It makes the reorganization of the topology possible which is normally completed automatically Furthermore it contains so called DUMP functions which pass information concerning the topology or spatial index to standard output v clean The module v clean allows a user to change and or repair the topology of a vector file At present twelve topolo
172. tion are provided in the QGIS Wiki 20 18 5 Processing GPS data The QGIS GPS plugin offers the possibility to import and or export GPS data in the GPS eXchange file format of the GPS device Lade GPX Datel importiere andere Datei Von GPS herunterladen In GPS hochladen Description GPX ist das GPS eXchange Dateiformat welches gebraucht wird um Informationen zu Wegpunkten Routen und Spuren zu speichern Selektiere eine GPXdatei und dann selektiere den zu ladenden Objekttyp Datei Objekttypen Figure 48 QGIS GPS plugin Thus QGIS offers the possibility to read created tracks as a layer by help of the GPS device If required this can be saved as GRASS dataset 18 6 Geospatial bookmarks In QGIS 0 7 it is possible to place geospatial bookmarks So you can jump directly to a place only by clicking on the bookmark GDF Hannover Courses 125 18 7 Creating analog maps with QGIS Name Project Extent Id Europe 2 59152 39 6019 21 9833 59 1092 2 South lower saxony 9 03582 51 0725 11 2874 52 8598 3 GDF Office 9 62746 52 2877 9 89658 52 5013 4 Figure 49 Geospatial bookmarks This makes it easy to zoom to a given extent in large projects 18 7 Creating analog maps with QGIS In chapter 17 some Free Software packages has been pointed out which can be used for creating analog maps Since version 0 7 QGIS also has a promising module for creating simple map layouts
173. tribute values of individual fea tures points lines boundaries and centroids by selecting them with the mouse The layer allocation the category value as well as the key column are displayed as additional information Optionally the encoding can also be controlled when saving attributes The current possibilities are utf 8 ascii iso8859 1 and koi8 r Open settings allows users to make different basic settings for the digitization process This includes the function for changing the symbol color for the display in the monitor symbology The setting of the snapping thresholds done in pixel units or map units settings Users can also create an attribute table Table The determination of background maps can be carried out on whose basis it is supposed to be digitized This can deal with several maps in vector or raster format background Exit After the digitization is finished leave the module v digit with the Exit Button All edits are saved within the map as well as and an automatic reorganization of the topology will be done Sample application for digitization A few topographical information based on the TK 1 24000 see figure 21 of the Spearfish region are supposed to be digitized as an example of digitization The topographical map for the GRASS example dataset Spearfish has explicitly been released by the South Dakota Geological Survey SDGS for teaching purposes with GRASS GIS This is already prepared and can b
174. u are concerned with is not listed there you can ask us about it by sending us email at mailto licensing gnu org lt licensing gnu org gt GDF Hannover Courses 130 20 GNU Free Documentation License Version 1 2 November 2002 Copyright 2000 2001 2002 Free Software Foundation Inc 59 Temple Place Suite 330 Boston MA 02111 1307 USA Everyone is permitted to copy and distribute verbatim copies of this license document but changing it is not allowed PREAMBLE The purpose of this License is to make a manual textbook or other functional and useful document free in the sense of freedom to assure everyone the effective freedom to copy and redistribute it with or without modifying it either commercially or noncommercially Secondarily this License preserves for the author and publisher a way to get credit for their work while not being considered responsible for modifications made by others This License is a kind of copyleft which means that derivative works of the document must them selves be free in the same sense It complements the GNU General Public License which is a copyleft license designed for free software We have designed this License in order to use it for manuals for free software because free software needs free documentation a free program should come with manuals providing the same freedoms that the software does But this License is not limited to software manuals it can be use
175. uitable for dis play by d text d vect chart d vect d what rast d what vect d where d zoom Displays charts of GRASS vector data in the active frame on the graphics monitor Displays GRASS vector data in the active frame on the graphics monitor Allows the user to interactively query the category contents of multiple raster map layers at user specified locations within the current geographic region Allows the user to interactively query a vector map layer at user selected locations within the current geographic region Identifies the geographic coordinates associated with point loca tions in the active frame on the graphics monitor Allows the user to change the current geographic region settings interactively with a mouse db commands Command Description db columns list all columns for a given table db connect Connect to the database through DBMI db copy Copy a table Either from_table optionaly with where can be used or select option but not from_table and select at the same time db describe Describe a table in detail db drivers List all database drivers db droptable db execute Execute any SQL statement db login Set user password for driver database db select Select data from database db tables List all tables for a given database db test Test database driver database must exist and set by db connect g commands GDF Hannover Courses 1
176. using the button settings gt Table see figure 22 The next step is to zoom into the region east of Spearfish again see figure 21 and to start digitizing the lines by clicking on the button digitize new line Afterwards choose a primary line in the monitor which should be digitized with the left mouse button The assignment of the mouse buttons can be found in the GUI Here it is also possible to determine the layer entry and the kind of the allocation of the category values GDF Hannover Courses 81 11 6 Digitizing with GRASS Attributes New record was created cat 4 toene p i Assume data encoding as Figure 23 Attribute entry during digitization According to the completion of the digitization of a line a graphical window is opened in which it is possible to assign additional attributes according to the attribute columns defined beforehand see figure 23 In this exercise the category value is supposed to be supplemented by the elevation of the line Click in the window and enter the elevation e g 4200 in the column height and then click on the button submit in order to adopt the new entry in the attribute table This is confirmed by the message Record successfully updated Once the digitization is complete exit the module v digit with the button Exit Thus the map contour_lines is automatically saved and its topology is built Building topology 825 primitives registered O a
177. v db connect p roads_hospital Note If the map roads_hospitals would be deleted at this place please consider that all attribute tables connected to this map are deleted this also includes the attribute tables hospitals and roads see chapter 10 3 This risk can be avoided by copying the attribute data to be connected In the following the hospitals and the roadnet are automatically connected and saved in a new map roads_hospitals GDF Hannover Courses 88 12 4 Assignment of the regions of optimal achievability Create connecting lines between hospitals and roads v distance p from hospitals to roads output roads_hospitals_connect upload dist column dist Patch connecting lines with roads and hospitals v patch in roads_hospitals roads_hospitals_connect out hospitals_net_pre correct topology v clean in hospitals_net_pre out hospitals_net tool break snap clean up g remove vect hospitals_net_pre hospitals_pre The map hospitals_net now contains the roadnet the hospitals and the connecting lines between both Furthermore category values are allocated to the hospitals via the internal layer 2 These category values are used as starting points for the calculation of the achievability 12 4 Assignment of the regions of optimal achievability After the basedata have successfully been edited and prepared the calculation of the regions is now supposed to be carried out Due to their distance along the roadnet the hospit
178. ve frame on the graphics monitor d path Find shortest path for selected starting and ending node d profile Interactive profile plotting utility with optional output d rast arrow d rast edit d rast d rast leg d rast num d redraw d resize d rgb d rhumbline d save d slide show d split d text freetype d text Draws arrows representing cell aspect direction for a raster map containing aspect data d rast edit Displays and overlays raster map layers in the active display frame on the graphics monitor Displays a raster map and its legend on a graphics window Overlays cell category values on a raster map layer displayed to the graphics monitor d redraw Resizes active display monitor Displays three user specified raster map layers as red green and blue overlays in the active graphics frame Displays the rhumbline joining two user specified points in the active frame on the user s graphics monitor Create a list of commands for recreating screen graphics Slide show of GRASS raster vector maps Divides active display into 2 frames amp displays maps executes commands in each frame Draws text in the graphics monitor s active display frame using TrueType fonts Draws text in the active display frame on the graphics monitor using the current font Prosecution on next side GDF Hannover Courses 140 Prosecution Command description d title Outputs a TITLE for a raster map layer in a form s
179. w project regions 004 26 GDF Hannover Courses iii Contents 4 5 2 Creating a GauB Kriger projectregion 2 00007 26 4 5 3 Creating a XY project region 2 22000 eee ee eee 29 4 5 4 Creating an UTM projectregion 0000 eee eee 29 4 5 5 Creating a latitude longitude project region 4 30 4 6 Deleting maps and projects 0 0 2 ee ee 31 5 Data import 32 5 1 Importing raster formats 2c Ke Be ose RRS De eke ea Me ee ee a eS 32 5 2 Importing vector data oo kh ee Sue YS we eee Oe oe ee ee Ye ee 34 5 3 Importing sites bh 844 A446 eh bee SSL ESER SES Eee e hE SE EHS 35 6 Georeferencing 38 6 1 Preparation for georeferencing ete ahs ae A es Yak Mae tar eects My Meee ae ME ee 38 6 1 1 __The optimal scan resolution 2 1 2 2225 26 ba edd ee Ra Ge es 38 6 1 2 Creating the needed projectregions 000 0000 39 6 2 Georeferencing procedure 2 a a 40 6 2 1 Choosing control points Seago es Se Se ae ES Bee Ree ES 40 6 2 2 Determining the correct transformation 0
180. with the inland waterways v overlay ainput pol_borders binput inlandwaterways output lakeinborders operator or When controlling the resulting map s attribute table both category values of the input maps are con served A joint table was created with each column assigned a corresponding prefix a_ or b_ GDF Hannover Courses 73 11 3 Data extraction indicating in the columnheader the source dataset 11 2 2 Data intersection When two vector maps are intersected the resulting map only contains those areas which occur in both input maps All other fields fall out v overlay ainput pol_borders binput inlandwaterways output borderswherelakes operator and In this case the th resulting map shows that only areas of the inland waterways persist 11 2 3 Data cutout Data cutout is the opposite of data union The resulting map shows the features in ainput not overlayed by features in binput v overlay ainput pol_borders binput inlandwaterways output borderswherenolakes operator not 11 2 4 Data overlay During the overlay data features of ainput or binput are adopted as long as ainput is not over lain by binput The following example shows that the features of the maps inlandwaterways and pol_borders are adopted in the new map bordersoverlakes as long aS inlandwaterways is not overlayed by pol_borders v overlay ainput inlandwaterways binput pol_borders output bordersoverlakes operator xor 11 3 Data extrac
181. y interstate with r mapcalc r mapcalc interstate if roads 1 roads zero GDF Hannover Courses 55 9 4 Modification and assignment of colortables Creating buffer zones r buffer in interstate out interstate buf dist 100 250 500 Control d rast leg interstate buf A Figure 17 Buffering raster data with r buffer The resulting map shows the interstates with the three previously defined buffer zones The spec ification of the buffer width is always referred to the middle of the feature to be buffered in this case interstate roads and is calculated in map units e g meters defined by the location The units can be queried in GRASS via the module g proj p g proj p PROJ_UNITS unit meter units meters meters 1 0 The conversion of a raster map into vector datamodel can be found in chapter 13 1 9 4 Modification and assignment of colortables The values available in an image file are visually coded by GRASS via a colortable After creating a raster image the rastermap is assigned to with few exceptions the default colortable rainbow There are several ways to create a map specific colortable One of the standard colortables can be assigned using the module r colors GDF Hannover Courses 56 9 5 Map statistics r colors map raster map color standard table r colors map raster map color special table color options aspe
182. y Exponent arithmetical 5 Rate Modulo arithmetical 4 Division arithmetical 4 Multiplication arithmetical 4 Addition arithmetical 3 Subtraction arithmetical 3 equal logical 2 l unequal logical 2 gt greater than logical 2 gt greater than or equal logical 2 lt less than logical 2 lt less than or equal logical 2 amp amp and logical 1 II or logical 1 pre separation operator arithmetical GDF Hannover Courses 99 15 2 Features in r mapcalc 15 2 Features in r mapcalc Table 13 Features in r mapcalc Feature Meaning Type abs x return absolute value of x we atan x inverse tangent of x result is in degrees Fo atan x y inverse tangent of y x result is in degrees F cos x cosine of x x is in degrees F double x convert x to double precision floating point F eval x y Z evaluate values of listed expr pass results to z exp x exponential function of x F exp x y x to the power y F float x convert x to floating point F graph x x1 y1 x2 y2 convert the x to a y based on points in a graph F if decision options i if x 1 if x not zero 0 otherwise if x a a if x not zero 0 otherwise if x a b a if x not zero b otherwise if x a b c aifx gt 0 bif xis zero cifx lt 0 int x convert x to integer truncates isnull x check if x NULL log x natural log of x F log x b log of
183. y saved it is no problem to leave the module i rectify and GRASS again to verify the current settings of the target location or to change if necessary and to call the XY location and i rectify again 6 2 2 Determining the correct transformation The correct transformation is defined by the polynomial degree This depends on the degree of distortion at central perspective aerial views e g by the relief energy existing in the project region as well as on the quorum of available control points The greater the image internal distortion the higher the needed polynomial degree and the more control points are needed for an exact georeferencing see table 9 Too high polynomial degrees are however mathematically not reasonable As a rule of thumb correct internal image geometry e g scanned topographical maps as orthog onal projection requires a minimal quantity of control points and therefore a minimal polynomial degree Otherwise distorted internal image geometry e g historical map needs a higher quantity of control points and therefore a higher polynomial degree GDF Hannover Courses 42 6 2 Georeferencing procedure Table 9 Polynomial degrees for georeferencing Polynomial degree Minimum number of Module Control points 3 6 i rectify 10 15 A OI N If too few reference points are set for a chosen polynomial degree GRASS does not start the rectifica tion A guide for determining t
184. your document contains nontrivial examples of program code we recommend releasing these examples in parallel under your choice of free software license such as the GNU General Public License to permit their use in free software GDF Hannover Courses 138 21 Command Iindex The following index is a complete list of all GRASS commanads An up to date list can be found at the official GRASS GIS website at 12 under the section manuals d commands Command Description d ask Prompts the user to select a GRASS data base file from among files displayed in a menu on the graphics monitor d barscale Displays a barscale on GRASS monitor d colorlist Output a list of all available display colors with a configurable sep arator default is comma d colors Allows the user to interactively change the color table d colortable To display the color table associated with a raster map layer d erase Erase the contents of the active display frame with user defined color d extend Set window region so that all currently displayed raster vector d font freetype d font d frame d geodesic d graph d grid d his d histogram d info d legend and sites maps can be shown in a monitor Selects the font in which text will be displayed on the user s graph ics monitor Selects the font in which text will be displayed on the user s graph ics monitor Manages display frames on the user s graphics monitor Displays a geodesic
185. zed results for the different regions of the earth In general a sufficient exact basic for the localization of the situation will be possible Table 2 Dimensions of some internationally used ellipsoids data rounded and examples of their usage location according to 7 Earth dimension Semi major axis Semi minor axis Usage location according to m m Bessel 1841 6377397 6356079 Germany Chile Netherlands Swe den Clarke 1880 6378249 6356515 Afrika France Hayford 1909 6378388 6356912 Belgium Finland Italy Spain WGS 1984 6378137 6356752 North America world wide 4 2 3 Datum There are numerous surveying points that are indicated as Datum and that can be calibrated by their heights data The following table contains a few examples for global and also regional datums The versions GRASS 5 4 and 6 0 both support datum transformation see Fig 6 Table 3 Some datums with their general application Datum Region Point of origin Ellipsoid WGS 84 Global Mass center of the earth WGS 84 NAD 1983 North America the Mass center of the earth GRS 80 Caribbean European 1950 Europe North Afrika Potsdam International 4 2 4 Map projection types In order to transfer the 3 dimensional form of the earth into a 2 dimensional plane to project a projection is needed GDF Hannover Courses 20 4 2 Projections TN azimuthal

An Introduction to the Practical Use of GRASS 6.0

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