Home

Visualizing Radar Signatures

Contents

1. In linear interpolation the value to be estimated is a blend of the two closest points Each of the points are weighed with how close they are to the new point The concept can be understood by examining figure 8 Given the points xo Yo and x Y we need to find the value Y for any given 17 56 x0 x x1 Figure 8 Linear interpolation Wikipedia The following equation describes the relationship y Yo x xo Y1 Yo x xo We introduce the parameter X to describe as the interpolation coefficient It describes the proportion of the distance from Yo to X you have traversed when you encounter X x xo x X9 Since Y is known we can calculate and insert it into the first equation to get the expression of Y shown in the equation below Wikipedia y l a yo ay Linear interpolation is slower than nearest neighbor interpolation but still quite fast and sufficiently accurate for most implementations 2 3 3 Cubic spline interpolation Spline interpolation is a more complex interpolation method which uses piecewise polynomials also known as splines There are a few different methods in this family of interpolation algorithms In the case of cubic spline interpolation cubic polynomials are used This method often produces very good results but is a lot more complex than linear interpolation 18 56 3 The Method This chapter describes how the different problems of the project where
2. bottom to top z points out of the screen negative values far away positive close normal x sinf fCurrPhi cosf fCurrTheta normal y sinf fCurrTheta normal z cosf fCurrPhi cosf fCurrTheta m pMesh gt m_vVertexNormals push_ back normal Vec3f vert if m_bDisplaceByScalars Vertices if m_bLogScale float scale m pMesh gt m_vVertexScalars nVertex 30 56 vert x vOrigin 0 4 vert y vOrigin 1 4 vert z vOrigin 2 4 logf m_pMesh gt m_vVertexScalars nVertex logf m_fRMin else if m bFourthRootScale tnormal x scale tnormal y scale tnormal z scale float scale m pMesh gt m_vVertexScalars nVertex powf m pMesh gt m_vVertexScalars nVertex 0 25f vert x vOrigin 0 4 vert y vOrigin 1 4 vert z vOrigin 2 4 else vert x vOrigin 0 4 vert y vOrigin 1 4 vert z vOrigin 2 4 else vert x vOrigin 0 normal x vert y vOrigin 1 normal y vert z vOrigin 2 normal m_pMesh gt m_vVertices push_ bac Zr tnormal x scale tnormal y scale tnormal z scale tnormal x m pMesh gt m_ vVertexScalars nVertex tnormal y m pMesh gt m_ vVertexScalars nVertex tnormal z m_pMesh gt m_vVertexScalars nVertex k vert Triangulating a sphere is very simple if you can afford not to have a closed surface The vertex normal calculations in this application allows the surface to be open without any visible effec
3. ring av upphovsr tten vid en senare tidpunkt kan inte upph va detta tillst nd All annan anv ndning av dokumentet kr ver upphovsmannens medgivande F r att garantera ktheten s kerheten och tillg ngligheten finns det l sningar av teknisk och administrativ art Upphovsmannens ideella r tt innefattar r tt att bli n mnd som upphovsman i den omfattning som god sed kr ver vid anv ndning av dokumentet p ovan beskrivna s tt samt skydd mot att dokumentet ndras eller presenteras i s dan form eller i s dant sammanhang som r kr nkande f r upphovsmannens litter ra eller konstn rliga anseende eller egenart F r ytterligare information om Link ping University Electronic Press se f rlagets hemsida http www ep liu se Copyright The publishers will keep this document online on the Internet or its possible replacement for a considerable time from the date of publication barring exceptional circumstances The online availability of the document implies a permanent permission for anyone to read to download to print out single copies for your own use and to use it unchanged for any non commercial research and educational purpose Subsequent transfers of copyright cannot revoke this permission All other uses of the document are conditional on the consent of the copyright owner The publisher has taken technical and administrative measures to assure authenticity security and accessibility According to intellectual property
4. Create Mesh Button 52 56 Create Mesh Object Ea Data Set Mesh Options Mesh Type C profects skolalexiobb BaseToolldetdist bas Mesh Type Options C iprojectsiskolalexjobbiBaseToolidetdist base v Use Displacement Dela Set List ju mare pecans Phi Start Phi Stop Phi Samples 10 25 Gor 1441 Se np E SN Theta Samples 30 0 30 0 181 Scaling Type emove Data Set Normal Scaling 3 Specification Data Add Sector To Set Mesh Label Mesh 3 The Mesh Type Choice Box lets you chose between Square Sector and Ellipse Sector The square sector cuts a square sector from phi start to phi stop and theta start to theta stop out of the data set The ellipse sector does the same but with an elliptical cut discarding data in the corners Unchecking the Use Displacement Check Box will put the values for all angles at the same distance from the origin forming a perfect sphere for a full data set Checking it will displace each value proportional to itself in the direction of the normal forming an object that is easier to analyze The Use Zero Padding Option is useful if the data set contains a very limited number of theta angles It will add two theta angels one above and one below with only zeros This makes the object visible even if it s just one angle thick Only use this option with data sets that are not full or if you limit the theta angles shown It does nothing for phi angles since data sets are assumed to contain full range in phi for all theta
5. Shag UA 9 2 1 2 Inyerse Synthetic Aperture Radar ata 9 DV Stealth rs O a oan key Eae aaa T e a a a E a bane E eia neate 9 Dal gs Detection AO As 10 A oe n cn bow e atin a ea T a a i 10 ZN Local COOT AIM ALE SP ACE sc basen iasiG cae ee NE E Gay Sica 10 22 2 World coordinate PCC fess die A A E pa AE ATE anette 11 ER A E A NN E AA 11 22A 3D SCTE CIES A 12 22 9 Local reflection Mo a ai 14 E A AA 15 227 NS A ns benet en Sic cae coasted Fogel loa A ER ASL SAN at ne eco ris au te uence tune 16 2 2 8 Generating vertex A E er r rn Rs rr ner n rer r rn n rna 16 2 29 N BUCK Shad TS isteir uysa iieii aiaee iis Uls sne sens er iae ase kkr iis ia We souk es 17 2240 PEA MENOS A A Go dra cli 17 23 Interpolation 5005 hei sars rag nin a rd ans a sade ni Reina slain dud de 17 2 3 1 Nearest NETO HD OL cats 230 O 17 2 3 2 Linear interpolations di 17 2 3 3 Cubic spline Interpol esnie nieto ar oea aia a RER EA E a id 18 TE MEM OS ENEE EN TS NS US NEN SSR NAN ada dd 19 3 1 Spherical DIAM 19 LOSA AS A ea TUB E A AA hog ew eo N eles 19 3 3 Visualizing Specification Dita dis dota ica 20 3 4 Generate high quality ViSUaliZatiOD ssserssorssrrsrersresrrsrrsrrnesrrsrrssrrsrrsnnrsr ron 22 3 5 Tools languages and maintainability A a nen nr rr rr rn nr nr nn 22 A lmplenentati do si 24 4 1 Application DESTINA AAA AS 24 4 2 Rendering recia 28 AA DESTA Eo anig aTe E A E E E DO 29 4 41 Optimizations d aia atea 29 4 4 2 Minter POL AVION aa 29 M
6. also more detailed information about the options and settings in the application The manual is enclosed as appendix A 45 56 6 Discussion and conclusions This chapter discusses the results presented in chapter 5 and draws conclusions from these results It also contains recommendations for future work and improvements 6 1 Discussion In creating an application such as BaseTool the usual approach is to ask the end users what they want from the program and then try to implement as much as possible of those wishes In the BaseTool project the input from the end users was mixed In terms of general characteristics the requirements were well defined The end users wanted a good looking application that was fast easy to work with and easily maintainable When it came to actual features there was simply not enough input This is a common scenario in software engineering The application designer asks the end users what they want and the end users reply by asking what the application designer can do In this project it meant that some of the features that were asked for and implemented are of limited value for the user With better interaction with the end users they could probably have been avoided How and if the application will be used remains to see In its current form it is very much a showcase of different techniques to visualize radar signatures The most likely uses are demonstrations and marketing rather than scientific analysis It pro
7. angles that are present Phi Start Phi Stop Theta Start and Theta Stop control what angles are shown Phi Samples and Theta Samples control the number of samples in phi and theta If the number of samples are changed bilinear interpolation will be used to determine the values in the new sample points The Scaling Type Choice Box lets you use normal logarithmic or fourth root scaling For logarithmic scaling log10 of the value is shown the smallest negative logarithm is shown as zero and all the other values are translated outwards which makes it hard to see what the values actually mean in terms of RCS or detection distance Fourth root scaling simply shows the fourth root of each value Taking the fourth root of RCS values roughly gives values that are proportional to the detection distance Using logarithmic or fourth root scaling for detection distance values probably doesn t make much sense 53 56 Specification Set Dialog To compare RCS or detection distance data to specifications you can manually create a data set with the Add Set Button in the Create Mesh Object Dialog The Sampling Controls are similar to those of creating a new Mesh Object except here you create a new data set instead The Base Value is the maximum value that the specification set will take in any point Later on you can modify the set by adding Specification Sectors but for overlapping sectors the smallest value will always be picked which is why the Base Value will ne
8. faster from the video memory than the system memory this is a very helpful tool especially for large meshes The drawback of using vertex buffer objects is that the data cannot easily be changed dynamically since it is locked in place in the video memory but that was not a problem in the case of BaseTool Vertex and fragment shaders were used to allow some dynamic control of the objects and to gain full control of the rendering pipeline Through the shaders the user can control transparency scale color and specularity of the objects Vertex normal calculation was implemented to allow specular shading The algorithm that was used also allows for some degree of edge preservation and was based on work by Nate Robins Robins 1997 The reason for using such a complex method is that the generated meshes often contain a lot of edges Other methods were tried but didn t produce acceptable results Another reason was that the CAD models did not contain vertex normals Usually hard edges are indicated by hand when converting from CAD format to a mesh but that wasn t an option in this project The idea behind the algorithm is described more in detail in section 2 2 8 Multiple render windows with shared context was implemented to improve performance and save video memory This means that rather than creating several copies of a mesh or other render data the information is shared between the different windows or canvases Limited support for this was availab
9. large data sets The spherical displacement concept is more intuitive and shows detail better than the colored sphere visualization 1 56 Preface For me coming into this project with a background in media technology rather than physics has been very interesting Radar was a new subject to me so the first thing I did was to read a few books on the subject I suspect this will often be the case when working with scientific visualization and that makes it all the more interesting This thesis project was carried out at SAAB Communication in Link ping during the spring of 2006 It was advertised on the Internet during the fall of 2005 and I d like to thank David Berg for pointing me to it without his help I would never have found it I also want to thank my supervisor Christer Larsson at SAAB Communication for his help and support and many interesting discussions Finally I want to thank my opponent Erik Carlson and my examiner Bjorn Kruse for their patience and support 2 56 Table of contents PADS UU AE U sass sire tte A ARS RS ARA 1 A 2 Table of contents A Ren RE 3 Table of HE a a a A E is as 5 Table OF tables iiisge wiciad oath aia 6 J TI EO DUG BOM eos passas osier kn Ses ANAR SRA SS e E E SRA SNI Gee E SNR A eta RASAR ABANA ERAN E ah T A TO 7 A NO 7 1 3 Further requirements and considera id 7 OO 9 2A RGAE i pata urs etanercept sk le H r Bern LG eee at a Oa Ua cca Aa a SR Dated 9 2 kl Radar Cross Section i maoni giles clone
10. of interest Finally the specular component is what is commonly known as a highlight practically an image of the light source reflected in the surface This reflection is only seen if the view point is near the 14 56 mirror direction of the light source This specular component is modeled by Is Iixcos Q Where is the angle between the viewing direction and the mirror direction and n is an index that simulates the degree of imperfection of a surface The surface becomes a perfect mirror as n reaches infinity In vector notation this is 1 1 R V R is the mirror direction and Y is the viewing direction Computing R is unnecessarily expensive Instead a halfway vector H is usually calculated H is the unit normal to a hypothetical surface that is oriented in a direction halfway between the light direction and the viewing vector such that H L V 2 Using this halfway vector the specular intensity can be calculated as follows I I N HY Using all this together gives an expression for the light reflected from a point Watt 2000 T 1 k 1 kg L N k N H Figure 6 Local reflection model Watt 2000 Figure 6 shows the vectors and angles used in the local reflection model 2 2 6 Gouraud shading In Gouraud shading Gouraud 1971 the light intensity is calculated in each vertex using the local reflection model method described in the previous section These intensities are then interpolated across the polygon
11. project The new implementation is undoubtedly better looking than the old and some of the images generated by the application could probably be used for marketing purposes Very little testing has been carried out on the user interface but comments have been positive from those who have tried to use the program and they have had no problem getting results with it More testing is required before any further conclusion can be drawn about the user interface 46 56 6 3 Future work and improvements Time was a major limiting factor in the project There are a lot of features that would add value to the application The ability to save a visualization with all the objects and settings as some sort of project would save a lot of time for the users Adding color bars and angle information would help the user understand and analyze the visualization Color bars would act as a legend explaining the color information instead of the currently showed min and max values that are not very intuitive Angle information in this case would be the ability to select a point on a surface and get a reading on what angle that point represents Selecting a point would also make it possible to show the exact distance value in that point Such information is crucial when using BaseTool in conjunction with software that analyze other radar data such as ISAR maps The screen capture function in the application should be improved so that it can produce images of arbitrary resol
12. two dimensional projection on the view surface the monitor screen Watt 2000 Figure 1 shows the different spaces that the vertices are transformed between to achieve the rendering and the different operations that are carried out in those spaces Local coordinate World coordinate View space 3D screen space Display space Space Space Compose scene Cull Hidden surface Object Define view Clip to 3D view removal definition reference Ea Rasterization Define lighting Shading Figure 1 Graphics pipeline Watt 2000 2 2 1 Local coordinate space The vertices of a polygon mesh objects are usually stored in their own coordinate system This makes it possible to for example set the origin in the middle of the object and align the axles with the object It also helps when creating local animations such as the walk of a 3D model of a human The face and vertex normals are usually also stored in the local coordinate system Watt 2000 10 56 2 2 2 World coordinate space This is a global coordinate space into which all objects are transformed so that their spatial relationship can be defined The light sources of the scene are also specified in the world coordinate space Animations of things moving in relative of each other are also done in world coordinate space 2 2 3 View space To be able to render the scene some viewing parameters has to be set The minimum definitions needed are a view point a view direction a view coordi
13. way of accomplishing this is the edge preserving method proposed by Nate Robins Robins 1997 It compares the angles between adjacent faces and splits the shared vertices 16 56 if the angle is larger than some given crease angle The vertices in these points will use the face normal instead giving a sharp edge The method is not perfect It will still miss some edges and split some vertices that are not on edges But it gives a better result for objects with edges than a purely smoothing algorithm would 2 2 9 Vertex Shaders A vertex shader is a small compiled program that is executed once per vertex and frame Such a program has to be loaded onto the graphics card itself and has a limited number of inputs and outputs The vertex shader is a replacement for the transformation and lighting parts of a standard graphics pipeline and is thus executed in world coordinate space The usual inputs to a vertex shader are position the vertex normal some often user specified uniform variables that are the same for all vertices and vertex attributes which are usually arrays of data with one value per vertex A vertex shader is supposed to output the transformed homogeneous vertex position It can also pass other variables to the fragment shader All the output variables will be interpolated across the polygon which means that the fragment shader will be executed a lot more than the vertex shader Vertex shaders are often used to manipulate the mesh or th
14. 74 Edwin Catmull 4 Subdivision Algorithm for Computer Display of Curved Surfaces Ph D Thesis Report UTEC CSc 74 133 Computer Science Department University of Utah Salt Lake City UT 1974 Thiirmer et al 1998 Grit Th rmer Charles A Wiithrich Computing Vertex Normals from Polygonal Facets Journal of Graphics Tools 3 1 1998 pps 43 46 Max 1999 Nelson Max Weights for Computing Vertex Normals from Facet Normals Journal of Graphics Tools 4 2 1999 pps 1 6 Lorensen and Cline 1987 William E Lorensen Harvey E Cline Marching Cubes A High Resolution 3D Surface Construction Algorithm Computer Graphics Proceedings of SIGGRAPH 87 Vol 21 No 4 pp 163 169 Wikipedia Linear interpolation http en wikipedia org wiki Linear_interpolationBaseTool User Manual 48 56 Appendix A Introduction BaseTool is an application that offers the user an easy way to visually analyze and demonstrate magnitude of RCS or detection distance data Features Show RCS data as a colored sphere or a displaced sphere Show the corresponding CAD models Rotate and zoom data freely Create and show specification sets and compare with RCS data Control transparency scale specularity and color of all objects 1 2 visualization windows that can both show several objects at once Small CAD window to show the CAD model at all times Save screen shots to jpg bmp or png files Resize all windows Fast loading times and high perform
15. APS O PASTE Generator a asians dana 30 4 4 4 Vertex Normals with Edge Preservation orel chase 32 AS Specification Sais ies a 33 4 4 6 EITliptiGal S ClOLS il dic 34 4 4 7 Rendering with Vertex Buffer Objects in OpenGL ooooonccnicconocononcconnnconccnonocancconnccnnccnnos 35 A THE V STNG A non secon derb Dnr ber sr sla ab vou aa vekare ETE ln dav Peau E as 36 3 56 4 4 9 Th tamiento 37 O A e Gumi te ome kia Ne hah cel HONAN A EEE 38 S A Spherical dis placemien bixiiva actcassccstiocasucacacs vac ccueusacbeas Vachon E lst Gteaneuewieadl casten A AE R 38 A vend ga ART SNR 38 5 4 D wnsampli gidat er cite ssirisssos cons tera css a Oy ast oN eres SDR RN Se cata E E Vat cone dace FRANS 39 5 5 Visualizing specification daa nen rsn rs rn cata toneudes 40 SG OPMIZAtIONS de Forsa eg esse A AAA Ad 41 5 Showing elliptical EOS a aa 42 PNR IRIT E ACC O Ted at a ued Ga aero 43 5 8 User MI AAA AAA AA 45 G DISCUSSION and CONCIUSIONS da 46 A ohn Sts yan ude ccbu ates ital neu algae ON SR e Yen TESEN AG 46 GALAS ls 46 6 3 Future work and PEO A Te 47 A 525205 cin tess osibns kassar sars eneyoanasinvtete naan nediedcosonsd UNS O TN ds K g ANS te Sa Eae a eTa ga E e E ESO 48 EAN PSs od riset earn A salter A user od un SAR Dawe pte a eae oat opal HORA See VR SEA SARS 49 4 56 Table Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Figure 14
16. Examensarbete LITH ITN MT EX 06 037 SE Visualizing Radar Signatures Tobias Forsl w 2006 06 07 Link pings universitet TEKNISKA HOGSKOLAN Department of Science and Technology Institutionen for teknik och naturvetenskap Link pings Universitet Link pings Universitet SE 601 74 Norrk ping Sweden 601 74 Norrk ping LITH ITN MT EX 06 037 SE Visualizing Radar Signatures Examensarbete utf rt 1 Medieteknik vid Link pings Tekniska H gskola Campus Norrk ping Tobias Forsl w Handledare Christer Larsson Examinator Bj rn Kruse Norrk ping 2006 06 07 Avdelning Institution Division Department 2006 06 07 Institutionen f r teknik och naturvetenskap Department of Science and Technology Rapporttyp ISBN Language Report category C Svenska Swedish Examensarbete ISRN LITH ITN MT EX 06 037 SE Engelska English O B uppsats O C uppsats Serietitel och serienummer ISSN D uppsats Title of series numbering O O URL for elektronisk version Visualizing Radar Signatures F rfattare Author Tobias Forsl w Sammanfattning Abstract It is important for the military to know as much as possible about how easily detected their vehicles are One way among many used to detect vehicles is the use of radar sensors The radar reflecting characteristics of military vehicles are therefor often rigorously tested With measurements and simulations it is possible to calculate likely detection distances to a ve
17. Figure 15 Figure 16 Figure 17 Figure 18 of figures Graphics pipeline Watt 2000 J sssconcs coats c cineri Wanised id 10 Viewing parameters Watt 2000 conociste tido est s 11 Parallel and perspective projections Watt 2000 oooooccnincninccnoccciocononcconccoonccnnnonancconccnos 12 Transformation of a box into 3D screen space Watt 2000 sssssressrsrerssrssrerorsrersren 13 Culling and hidden surface removal Watt 2000 sssssserssersrrsererorssrrsrrersrernrsrrsnrernrsrnsnrn 14 Local reflection model Walt 2000 2 ias 15 Weighting banda o 16 Linear interpolation Wi a a OA Edie 18 Spherical displacement m 2D iconos ralla ero dess Ner EA kg E S ES 19 2D BPE CHICANO datar ao 21 A cag cece sp ah das a a arcuate a dre NGE es RSS olje sma earn anon ea SR 24 Rendering a tease esa lid ds 25 User interface and tool inter Moraira edad anal 26 Color di 8 1 Te a E E AET E AMAGER ewe aya 38 Spherical displacement o a A AA SR NAR 38 DOSS MAR eS a eat stan 39 NS O O ARNE SEN SERA 39 Specular effects n a colored SP CIO sserserserrserserrsrrrsrrsrrsrresrrsrrsrrernrsr renen rs lien abntees 39 Figure 19 Downsampling ComparisOM c cceccceseeeseceseeeeceeeseeesceceseeeaeceseeeeeceseeeeeeeseeeeeeeeenseees 40 Figure 20 Specification AR 41 Figure 21 Elliptical sector in wireframe Mode viii eee irene cirio acid 43 Figure 22 Visualization window of the old VEO ii ia sti as 43 Figure 23 Menu of the Old O N
18. GL then sends the data through the vertex and fragment shaders Interactive parameters to the shaders are also sent via the sphere generator These parameters control the transparency color specularity and scale of the mesh When designing the user interface the main objectives were to make it flexible and easy to use These are often two conflicting interests since flexibility often also creates complexity The script language python and widget library wxPython was used to make the creation of the user interface 25 56 easier and faster Platform independent wxWidgets Python module wxPython C library pyOpenG OpenG C rendering OS specific OS specific gt GLEW module render canvases widgets Output Figure 13 User interface and tool interaction Figure 13 shows how the different tools used in the user interface interact as well as how the OpenGL calls are handled The normal interface widgets such as buttons sliders menus windows dialogs et cetera are created through wxPython The python module of the application contains wxPython instructions that describes how the application should look These instructions are sent through wxPython which is a thin wrapper around the much more complex wxWidgets C library WxWidgets contains functionality to ask the OS for its specific widgets to use This gives the application the look of a Windows XP application To be able to show OpenGL content you
19. N BG ete ee OO OS 44 Figure 24 User interface of the new Version sock 2 Jedi cep eacucti tenga gusts he deca caves Caveats daa 45 5 56 Table of tables Table 1 Specification sector MOS dis Table 2 Optimization tests 6 56 1 Introduction This chapter discusses the background and purpose of the thesis project and also contains the requirements and considerations implied by SAAB Communication 1 1 Background Information has always been a central part of warfare and this is even more so today The key problem for military forces is to gather as much information as possible while keeping the enemy guessing One of the most important means of gathering information today is through the use of radar therefore the research in this area is intense Since the 1950s researchers have been working on the problem of hiding vehicles from detection using so called stealth technology The most commonly known stealth vehicles are probably the American B 2 bomber and F 117A fighter aircrafts To make it easier to create and improve on stealth vehicles the radar reflections can be measured and analyzed to find weaknesses in the design One approach is to use Inverse Synthetic Aperture Radar ISAR to create a set of color coded images that show the magnitude of the reflections for several different angles These images can be projected onto a model of the vehicle itself to illuminate the parts that cause the most reflections The ISAR data also cont
20. Vertex Buffer Objects in OpenGL The vertex buffer objects technique allows the application to save data in the video memory This provides a major speed increase as discussed in section 4 3 The following code sample shows how the data Init is saved to the video memory tialize the mesh for rendering if vertex arrays are used stores vert tex arrays in video memory for fast access in rendering void CSphere RenderInit Store vertex array in video card memory glGenBuffers 1 amp m_nVBOVertexID glBindBuffer GL ARRAY BUFFER m_nVBOVertexID glBufferData GL ARRAY BUFFER m_pMesh gt m_nVertices 3 sizeof float m_pMesh gt m_vVertices begin GL STATIC DRAW Store vertex normal array in video card memory glGenBuffers 1 m nVBONormalID glBindBuffer GL ARRAY BUFFER m nVBONormalID glBufferData GL ARRAY BUFFER m pMesh gt m_nVertices 3 sizeof float m_pMesh gt m_vVertexNormals begin GL STATIC DRAW Store vertex attribute array in video card memory glGenBuffers 1 m nVBOAttribID glBindBuffer GL ARRAY BUFFER m nVBOAttribID glBufferData GL ARRAY BUFFER m_pMesh gt m_nVertices sizeof float amp m pMesh gt m_vVertexScalars 0 GL STATIC DRAW Store index array in video card memory glGenBuffers 1 amp m_nVBOIndexID glBindBuffer GL ELEMENT ARRAY BUFF glBufferData GL ELEMENT ARRAY BUFF 35 56 R m_nVBOInd
21. ains the information to make it possible to calculate the likely detection distances for a vehicle from all possible angles or at least an approximation of them 1 2 Purpose Military platforms usually have specifications involving radar cross section RCS The RCS is a measurement of the amount of the radar signal that is reflected back to the radar from the target The specifications are often broken up into different angular sectors for the platform These sectors correspond to different types of radar threats For each sector a maximum RCS value is typically specified These values will vary greatly across a threat sector and it is often very hard to meet the specifications for all sectors It is also hard to show what difference a change in the design will provide This project aims to create a tool able to visualize the overall radar reflectance properties of a platform as well as compare different measurements or simulations The tool should be highly interactive and able to highlight the different threat sectors to help showing that requirements have been met Such a tool may also be useful to educate military personnel about the radar signature of their vehicle 1 3 Further requirements and considerations The project was carried out at SAAB Communication who had already done some work in the area A tool called BaseTool that could calculate detection distances and show them as colored spheres had already been developed but SAAB felt more w
22. ance 3D visualization Getting Started Start by opening an ISAR data file and create a base file with the precalculation functions This will remove phase information and calculate an averaged RCS data set from the frequency data Next load the base file you ll notice the CAD model showing up in the upper left window the CAD window Now press Add Mesh in the options panel Depending on how you did the precalculation part one or more data sets will show up in the left list Pick one and edit the settings or just click Create Mesh to start with the default settings The dialog will close and your mesh will show up in the list in the Options Panel Select the mesh from the list this will allow you to control settings for that mesh To show the mesh in the Main Canvas check the box for Show on Main Canvas Alpha controls the transparency of the object scale controls the size in relation to other objects while zoom scales everything in all windows and specularity controls the direct light reflections The object is color coded with a mix of three colors the default is Red at maximum distance from the center Blue at minimum distance and Green in the middle These values can be changed per object To show two screens press the Split Window button This enables the secondary canvas and allows you to compare different data sets To create a specification set click Add Mesh then Add Specification Set Set the base value to the maximum value the s
23. attacked and solved and the tools that were used 3 1 Spherical Displacement The detection distance data was previously presented as a colored sphere or sectors of a sphere The key idea of the project is very simple Displace each value from a center point in the normal direction of the sphere with a distance proportional to that value instead of just showing it as a colored sphere The intention of this was to make it easier to detect small variations in the data Figure 9 Spherical displacement in 2D Since the values represent distances in some way spherical displacement was also considered to be a more intuitive way of visualizing the data Using spherical displacement will result in a visualization of the actual detection volume To understand the concept imagine a vehicle inside a transparent object The distance from the vehicle to any point on the surface of the transparent object describes the detection distance for that angle Figure 9 shows the concept in 2D Each point P is displaced a distance d in the normal direction of a sphere or a circle in the 2D case The distance d is the detection distance and the angle describes from what direction the vehicle has this detection distance In this 2D example the vehicle is seen from above with its nose pointing upward This is usually the case for the 3D visualizations as well but an elevation angle is also introduced to give a full sphere of angles 3 2 Scaling Since the rang
24. ave inconsistent ordering of the vertices in the triangles This causes some triangles to show as zero intensity unless dealt with The solution was to treat the object as a two sided object If the dot product between the light vector and the normal is negative simply invert the normal The vertex shader calculates the intensity according to the local reflection model described in section 2 5 Dynamic scaling is also done by the vertex shader Get the position vec4 pos gl Vertex Dynamic scaling pos x pos x fScale pos y pos y fScale pos z pos z fScale Ke Pass the scalar vertex attribute to the fragment shader scalarFrag scalarVert Calculate transformed position light vector and normal vec3 P vec3 gl ModelViewMatrix pos vec3 L normalize gl_ LightSource 0 position xyz P vec3 N normalize gl NormalMatrix gl Normal between normal and normal Two sided object if dot product light vector is negative invert if dot N L lt 0 0 Calculate eye vector and halfway vector vec3 E normalize P vec3 H normalize Eth Calculate ambient diffuse and specular intensities and pass them to the fragment shader Tamb 0 0 tarif max dot N L 0 0 Ispec pow max dot N H 0 0 50 0 Save transformed position gl Position gl ModelViewProjectionMatrix pos 4 4 9 The fragment shader In this project it is the j
25. aves suffer much less attenuation through the atmosphere than light waves and signals in the lower frequency ranges actually propagate over the visible horizon This makes it possible to detect targets long before they are visible optically Radars also work well at night when there is little or no ambient light to illuminate the target Knott et al 1993 The basic principle of a radar is to emit electromagnetic energy and listen to the echo to determine something about the surrounding environment Since the speed of electromagnetic waves is known it is easy to find the distance to the target by clocking the time between transmission and reception To find the location of the target the azimuth and elevation angles must also be determined This can usually be done by measuring the direction of the antenna since most radar antennas are a lot more sensitive in one direction Knott et al 1993 It is also possible to determine the velocity of the target because of the Doppler effect 2 1 1 Radar Cross Section Radar Cross Section RCS is a measurement of the amount of energy reflected by the object back towards the radar antenna It is defined as the effective area of reflection and is uniform in all incident angles only for a perfect sphere but for all practical objects it varies with the azimuth and elevation angles to the radar and therefore shows how detectable the object is to radar from different points of view The RCS also varies with the fre
26. bably works well as a tool to aid in discussions about test data and simulated data 6 2 Conclusions The main idea with the project was to explore the idea of using spherical displacement rather than just colored spheres The spherical displacement was implemented together with several other features resulting in the BaseTool application The admittedly few that has tested the application claim that the spherical displacement is indeed more intuitive and easier to work with in comparison with the colored spheres More testing would be required to properly assert this SAAB also wanted an optimization of the preprocessor code and a general improvement of loading times Section 5 6 clearly shows a significant improvement with loading times up to 200 times faster in the new version of the application Visualization of specification data was also implemented As seen in section 5 5 it is easy to find the points where the specifications are not met In reality it is very likely that mostly the flat sectors will be used because of their simplicity But the other methods could be used to prove a point if the application is used as a demonstration tool during a session discussing the specifications The Gaussian sector is unlikely to be used at all since it is very complex and not all control parameters are available in the application It was left in the application mostly for reference Achieving a high quality visual appearance was one of the aims of the
27. displacement is explained in section 3 1 Figure 14 shows the colored sphere approach of the old version while figure 15 shows the new spherical displacement The old method of visualization is still available in the new version Figure 14 Colored sphere Figure 15 Spherical displacement Both images show the same data but the spherically displaced data conveys it in a better way It shows both detail and the general appearance at the same time and it is a lot easier to get an idea of the magnitude of the variations in the data The color information is still available in the new version but it shows the same thing as the distances to the center By looking at the colors and the minimum and maximum values of the object one can see what values the colors represent 5 3 Specularity The use of specular effects is mostly eye candy but also has some advantages when analyzing the data While good looking visualization is a motive in itself the specular effects also help in enhancing details on the spherically displaced meshes Figure 16 shows a spherically displaced detection distance mesh with specularity effects off and figure 17 shows the same mesh with 38 56 specularity on Geometric detail is more visible in figure 17 while color information is somewhat destroyed Figure 16 No specular effects Figure 17 Full specular effects Using specular effects on a colored sphere is not very useful Since the light source is located in the
28. e center The options that were implemented are shown below in table 1 21 56 Sector Type Value Flat min i Enes min max min Oxl byl kl gt Lo Elliptical P P P ine oo Hy Gaussian on S x 0 4 y10 4 min max min e Table 1 Specification sector modifiers Where min is the minimum value of the sector usually the original value The maximum value is max and describes the highest value that the sector will take The sector will take maximum value in the corners and the minimum value in the center The p value controls how fast the values decreases A high p value makes most of the sector use the minimum value and only the corners use the maximum while a lower value lets the maximum value control more of the sector A normal value of p would be 3 or 4 for the elliptically decreasing sectors The Gaussian sector creates a normal distribution curve over the sector It is not possible to assert that the Gaussian method creates a sector with the maximum values in the corners and the minimum value in the center The Gaussian sector should also have the standard deviation as an extra control parameter but it has been set to 0 4 for simplicity 3 4 Generate high quality visualization One of the key problems in the project was to generate good looking high quality visualizations of the data Scientific visualizations often have a rather dull and functional look to them but since one of the int
29. e normals in some way but also to do preparation calculations for the fragment shader 2 2 10 Fragment Shaders Fragment shaders are executed in a later stage in the rendering pipeline After passing the vertex shader vertices go through culling clipping hidden surface removal until they reach the fragment shader It is the job of the fragment shader to calculate the color of a fragment It gets input from uniform variables just like the vertex shader and it also gets varying attributes from the vertex shader While the vertex shader is required to output a position the fragment shader is allowed to discard the fragment If not it should output a color and an alpha value Using the colors of the different fragment together with the alpha values and the z buffer pixels are created by the fixed pipeline in the next step after the fragment shader is executed 2 3 Interpolation When dealing with discrete data it is quite common to find that you need the value in between two samples Interpolation is the art of estimating that value This chapter lists and describes some of the most common interpolation techniques They are described for one dimension but can easily be applied for two or more dimensions as well 2 3 1 Nearest neighbor This method is quite simple as the name implies you just pick the nearest neighbor If two samples are equally close either one will do This method is very fast but not very accurate 2 3 2 Linear interpolation
30. e of the data is so high it is often hard to see small variations One way to counter this was the spherical displacement A method to further increase the visibility of small variations was 19 56 the use of different scaling options Before displacing the values they can be scaled for instance using logarithmic scaling The use of a logarithmic scale presents a problem in the visualization Values between zero and one suddenly becomes negative and while this would be possible to visualize if values are displaced from a flat surface it becomes completely confusing if values are displaced spherically from a point The negative values then end up on the opposite side of the sphere One solution to this is to add the inverse minimum value to all values This pushes everything outwards and creates a shape that is less confusing It may be misleading that the center point of the visualization is not zero but an arbitrary negative number The method also falls apart if the RCS is exactly zero in some point since that would displace everything infinitely Another solution is to take the fourth root of the value This is somewhat simplified what the preprocessor module already does to convert RCS values to detection distances The detection distances also depend on other variables than the RCS such as the sensor and dampening but is essentially proportional to the fourth root of the RCS This means that fourth root scaling is rather useful for visual
31. ed Perspective projection is much more common since it provides a feeling of depth in the scene In perspective projection objects that are far away appear smaller than objects that are close Figure 3 shows the difference between perspective and parallel projection Figure 3 Parallel and perspective projections Watt 2000 While it would be possible to go directly from view space to display space there are a few operations that benefit from an intermediate state This is the 3D screen space When going from view space to 3D screen space points are transformed so that a parallel projection would give a perspective projected scene Figure 4 shows this transformation on a box 12 56 Figure 4 Transformation of a box into 3D screen space Watt 2000 Clipping is the process of discarding all polygons outside the view volume as well as clipping the polygons that intersect the view volume One of the neat things with 3D screen space is that the sides of the view volume becomes parallel the view volume in fact becomes a box rather than a pyramid and this box is also aligned with the coordinate system Rather than comparing coordinates with plane equations you now simply have boundaries in x y and z to compare against which is much more efficient Watt 2000 In the culling process we removed polygons that were located on the back side of objects but we still need to remove polygons that are obscured by oth
32. elowInside IsInsideEllipse r x xStep y a b x xStep y a b x ytyStep a b x y yStep a b E anaa llips squarelndex defines which of the four neighbours are inside th basically sets the 4 bits with lowest significance 0010 2 gt bRightInside is true 1001 9 gt bleftInside and bBelowInside are true ete int squarelndex 0 if if IE IE bLeftInside squareIndex 1 bRightInside squareIndex 2 bAbovelnside squareIndex 4 bBelowInside squareIndex 8 Check if any neighbours are inside th llips if so use a point on the ellipse uses the simple fact that x a cos theta y b sin theta defines th llips switch squarelndex case 0 All neighbours outside return false case 1 Left x a cosf asinf y b return true case 2 Right 34 56 x a cosf asinf y b return true case 4 Above y b sinf acosf x a return true case 8 Below y b sinf acosf x a return true case 5 Left and above x a cosf asinf y b return true Case 6 Right and above x a cosf asinf y b return true case 9 Left and below x a cosf asinf y b return true case 10 Right and below x a cosf asinf y b return true default The other cases only apply to concave objects and are ignored return false 4 4 7 Rendering with
33. ended uses for the application was producing images for marketing it was important to produce good looking results To achieve this a decision was made to use smooth shading with the Phong model described in section 2 2 7 Using smooth shading also allowed for the use of good looking specular effects For smooth shading to produce sufficiently good results high quality vertex normals had to be calculated Since both CAD models and the generated meshes contain a lot of hard edges it was decided to use the smooth normal generation with edge preservation algorithm created by Nate Robins Robins 1997 For an even better result this was coupled with the weighting by angle algorithm proposed by Th rmer and Wiitrich in 1998 Th rmer 1998 These algorithms are described in section 2 2 8 3 5 Tools languages and maintainability As described in section 1 3 SAAB wanted the application to be easily maintained To make it easier to change the user interface and add new features it should be separated from the core of the program A script language controlling the application and the user interface would be helpful for future programmers and would also add some structure to the application Creating a user interface in a script language is also helpful since it does not require the programmer to compile the program every time a new feature is tested The user interface and part of the rendering controls was programmed in the script language Python It was chosen
34. er objects This is called hidden surface removal There are several different approaches to hidden surface removal but the most commonly used is the Z buffer algorithm The Z buffer algorithm was invented by Edwin Catmull in 1974 Catmull 1974 The Z buffer algorithm works in 3D screen space for much the same reasons as clipping In 3D screen space the camera can be said to be infinitely far away making lines from the camera towards the scene parallel This means that if a point x y on a polygon has a higher z value than the same point on another polygon then the first point is hidden The Z buffer algorithm basically uses this fact by creating a buffer containing the smallest z value for each pixel Figure 5 shows the difference between culling and hidden surface removal where step a is culling and b is hidden surface removal 13 56 a b Figure 5 Culling and hidden surface removal Watt 2000 What now remains is the process of creating pixels out of the 3D dimensional content This is done by rasterization and shading The rasterization is the process that actually creates pixels from the edges and polygons and the shading process is what colors the pixels A programmer often has little interest in controlling the rasterization process but shading is one of the most interesting aspects of 3D computer graphics 2 2 5 Local reflection models A local reflection model enables the calculation of the reflected light intensity from a poi
35. esh Object Data Set Add Specification Sector Sector Type C projectsiskol Eliptical in Phi and Theta C tsiskol Min Value Phi Start Phi Stop 0 360 mreta ARSE CORTRA stop 90 90 Cena Specification Data Add Sector To Set Mesh Label Mesh 3 Cancel Create 55 56 Precalculation Dialog The Precalculation Dialog is accessed via the File Menu item Create BaseTool file from ISAR data To create a base file first select an input file with the Browse Button Choose the wanted Sensor and Background options The Data Redundancy option controls how the redundant data is handled There are usually more than 360 degrees of data in the phi orientation so you can either average the redundant data or simply remove it The Data Type controls the output data type you can get raw magnitude of RCS data detection distances or both If you only want RCS data you don t need to care about the Sensor and Background options The Frequency Band options are not yet implemented and cannot be changed Create a Base fool file Select Input File C projects skola exjobb BaseTool GR2_small h5 Options Frequency Bands 5 40000009537 to 5 90000009537 Sensor P590 simple Background Free space Data Redundancy Average redundant data Data Type Magnitude of RCS only Select Output File C projects skolal exjobb BaseTool test base 56 56
36. et will have After creating the set select it from the list and click Add Specification Sector You can add several sectors to one set When finished just click Create Mesh as with a normal mesh 49 56 Menus The menus of the application contain the following items File Create BaseTool file from ISAR data This allows you to create a base file for further use in BaseTool The ISAR data needs to be in hdf5 format File Open BaseTool file Opens a base file and adds its data to the project File Capture Image Creates a screen shot of the application and saves it as a jpeg png or bmp image file File Exit Exits the application Options Wireframe Toggles wireframe rendering mode on and off 50 56 Dialogs and Panels Options Panel The Options Panel is located on the left hand side of the application and contains options for Mesh Objects The Mesh Objects List shows all mesh objects You can select a mesh object by clicking it in the Mesh Objects List Options for the mesh will then activate in the Options Panel The Alpha Slider controls the transparency of the current mesh The Specularity Slider controls the shininess of the current mesh The Scale Slider controls the relative scale of the current mesh Check the Main Canvas Checkbox to show the mesh on the Main Canvas Check the Secondary Canvas Checkbox to show the mesh on the Secondary Canvas Click the Show Hide Secondary Canvas Button to show or hide the Seco
37. exID ee R m_pMesh gt m_nIndices sizeof UINT amp m pMesh gt m_vindices 0 GL STATIC DRAW m F a m F py To access the data during the actual rendering pass the following code can be used This render method uses vertex arrays that have previously been uploaded to the video memory Probably the fastest method available void CSphere Render Set vertex array from video memory glBindBuffer GL ARRAY BUFFER m nVBOVertexID glVertexPointer 3 GL FLOAT 0 char NULL Normal array glBindBuffer GL ARRAY BUFFER m_nVBONormalID glNormalPointer GL FLOAT 0 char NULL Vertex attribute array glBindBuffer GL ARRAY BUFFER m nVBOAttribID glVertexAttribPointer m nAttribLocationID 1 GL FLOAT 0 0 char NULL Set index array from memory and draw glBindBuffer GL ELEMENT ARRAY BUFFER m _nVBOIndexID glDrawElements GL TRIANGLES m pMesh gt m_nIndices GL UNSIGNED INT char NULL 4 4 8 The vertex shader The use of shaders allow for better control over the rendering pipeline How they work and where they fit into the graphics pipeline is described in section 2 2 9 In this project the vertex shader is used to calculate the specular component of the light intensity Some of the CAD models used in the project are does not have uniform orientation of the face normals or rather they h
38. flection of sunlight sound radar and laser illumination and also reflection of the ever present ambient radar waves from unrelated sources often called splash track Lynch 2004 2 1 3 Detection distances To calculate the detection distances for a platform more information than the RCS is needed As the RCS is a measurement of the reflected energy it is possible to calculate how much energy will be reflected to the radar sensor if the amount of energy that is sent out is known The next consideration that has to be made is how much reflected energy is needed for the radar sensor to be likely to detect the object The frequency of the radar sensor is also needed since the RCS varies with the frequency of the incoming signal If the RCS of the object the output power and frequency of the radar sensor and the reflected energy needed to detect the object are all known it is possible to calculate the likely maximum detection distances The magnitude of the response for different angles is proportional to the power of the incoming radar signal but as the RCS varies with the frequency it should be noted that the detection distances are very much dependent on the radar sensor and calculations need to be made for different kinds of sensors to get a good picture of the radar reflectance properties of the platform 2 2 Computer graphics The purpose of a graphics pipeline is to take a description of a scene in three dimensional space and map it into a
39. for several reasons It is an open source project which is in line with the requirements of the project it has a multitude of open source modules available and since it was used in the previous version of the application there were people able to give support on the language available at SAAB but the major reason was that SAAB 22 56 explicitly asked that the project continued to use python Several of the python add in modules were also used in the project For instance wxPython which is a wrapper for wx Widgets that provides access to the platform specific user interface widgets for Windows Apple and Linux platforms Another module that was used is PyOpenGL which provides access to most of the OpenGL functionality within Python PIL or Python Imaging Library was used for saving captured screen shots as image files The Numeric module was used for its excellent mathematical operations on matrices which was especially useful in the preprocessor module of the application PyTables was used as an interface to the HDF5 hierarchical file format that was used in the input files as well as the intermediate files The base functionality and rendering facilities of the application created for this thesis was built in C using OpenGL as the interface to the graphics hardware The Visualization Toolkit VTK was used in the early stages of the project but was eventually replaced by the C OpenGL module to add more control and better performance to the ap
40. hase information intact meaning that each angle and frequency is represented by a complex number Before detection distance values can be estimated the data radar cross section values must be calculated for all available angles This is done by averaging the frequency data and calculating the magnitude of the complex numbers After this processing we have one value per angle which is the RCS 24 56 The data is read from the intermediate BaseTool file via pyTables to an array in python Python then sends it into the data array manager class in the C module The user can now choose what parts of the data to create a mesh from the resolution of the mesh and what kind of mesh to create The data array manager resamples the data into the new resolution and sends it to the sphere generator which creates the mesh Using vertex buffer objects the sphere generator saves the mesh onto the graphics card via OpenGL and during rendering the data is read directly from the video memory Render Call pb Interaction Figure 12 Rendering Figure 12 shows the information flow in the rendering process The rendering is controlled by the python module Most of the instructions to OpenGL such as navigation are sent directly from the python module via pyOpenGL The call to render the mesh itself is sent via the sphere generator class in the C module The sphere generator asks OpenGL to read from the video memory where the data was previously stored Open
41. he C module also go through GLEW Before making a call to a function in the C module all that needs to be done is to set the correct canvas in python since the python module controls the canvases As shown in figure 13 most of the application is actually platform independent To make it possible to run the application on another platform than Windows it would be necessary to change and recompile the C module and replace the current GLEW version with the correct version for the new platform 27 56 4 2 Rendering Techniques The data sets visualized by the BaseTool applications are quite large and complex Because of this the objects that are rendered tend to be complex as well often containing several million triangles The graphic hardware of today can handle these triangles but only if the right rendering techniques are used and the most common bottlenecks are avoided To achieve the high performance that the application currently produces the rendering engine was reworked several times The most significant increase in performance came from the use of vertex buffer objects VBO The vertex buffer objects used to be an extension of OpenGL but are part of the core language since version 2 0 They allow saving vertex and index arrays in video memory rather than system memory Instead of copying the data from system memory to video memory every frame it can simply be read from the video memory directly Since the graphics card reads data a lot
42. he following code sample shows how the different types of sectors discussed in 3 2 was implemented for int i iStart i lt iEnd i for int j jStart jJ lt jEnd j x float i iStart 2 iRange float iRange y float j jStart 2 jRange float jRange switch mode case SECTOR MODE FLAT value fMin break case SECTOR MODE LINEAR THETA value f Min fMax fMin fabsf x break case SECTOR MODE LINEAR PHI value fMin fMax fMin fabsf y break case SECTOR MODE LINEAR BOTH value fMin fMax fMin fabsf x fabsf y 2 0f break case SECTOR MODE SPHERICAL THETA value fMin fMax fMin fabsf powf x xPow break case SECTOR MODE SPHERICAL PHI value fMin fMax fMin fabsf powf y yPow break case SECTOR MODE SPHERICAL BOTH value fMin fMax fMin fabsf powf x xPow fabsf powf y yPow 2 0f break case SECTOR MODE GAUSSIAN PHI value fMax fMax fMin expf 0 5f fabsf powf y yStd yPow break case SECTOR MODE GAUSSIAN THETA value fMax fMax fMin expf 0 5f fabsf powf x xStd xPow break case SECTOR MODE GAUSSIAN BOTH value fMax fMax fMin expf 5f fabsf powf x xStd xPow fabsf powf y yStd yPow break 33 56 4 4 6 Elliptical Sectors When analyzing a sec
43. he original data is also possible but probably has little use The interpolation method used is bilinear interpolation which is described in theory in section 2 3 and the implementation in section 4 4 2 It is possible that a more advanced interpolation method such as bi cubic spline interpolation would give better results but as the interpolation is a heavily used feature in the application this would have a big impact on the performance Figure 19 Downsampling comparison 5 5 Visualizing specification data One of the major new features in this version of BaseTool is the ability to show specification data The process of creating these specification data sets is described in the user manual in Appendix A After such a set is created it is treated mostly like a normal data set The main difference is that the default settings for color transparency and specularity are different for specification sets Figure 19 shows a fictional specification set with the default appearance settings and containing a detection distance set It is very easy to see where the detection distances intersect with the specification set and thus fail to meet the specifications 40 56 Figure 20 Specification sets The specification set in figure 20 uses elliptically diminishing sectors as described in section 3 4 Most of the different sector settings are easy to use and produce good results but the Gaussian method is rather complex and doesn t always produce good
44. hicle from different angles This process often produces very large data sets that are hard to analyze This thesis discusses and implements a method for visualizing the detection distance data set and also discusses a lot of related issues with a focus on computer graphics The main concept is called spherical displacement and the idea is to visualize the detection distances as a surface with the imagined vehicle in the center point Detection is likely inside the surface but not on the outside This concept is the next step from the colored sphere where the colors represent the detection distance which was previously used The thesis project resulted in a visualization tool that uses the new concept and can handle large data sets The spherical displacement concept is more intuitive and shows detail better than the colored sphere visualization Nyckelord cose YS bs Aste Lank Keyword visualization scientific visualization radar radar signatures LINKOPING UNIVERSITY Se ELECTRONIC PRESS o De sane Upphovsratt Detta dokument halls tillgangligt pa Internet eller dess framtida ersattare under en l ngre tid fran publiceringsdatum under f ruts ttning att inga extra ordin ra omst ndigheter uppst r Tillg ng till dokumentet inneb r tillst nd f r var och en att l sa ladda ner skriva ut enstaka kopior f r enskilt bruk och att anv nda det of r ndrat f r ickekommersiell forskning och f r undervisning verf
45. ization purposes This method doesn t have the problem with negative values and is more intuitive 3 3 Visualizing Specification Data One of the key problems for the military industry is to show that they have met the specifications for the project This is already hard enough since the measurements are very expensive and the values are often simulated The specifications are usually in the form of different maximum values allowed for certain sectors The idea here is to visualize these specifications much like a normal dataset with spherical displacement If the specification data is shown like this but with transparency and no color information it is possible to show a specification set and the corresponding detection distance or RCS data simultaneously Where the detection distances show outside the specification set the detection distance doesn t meet the requirements This would be very much easier faster and more intuitive than searching the data sets for too high values by hand 20 56 Figure 10 2D specification data Figure 10 shows how it could look in 2D The black shape is the detection distance set and the red set is the specifications Wherever the black set is outside the red the requirements have not been met Currently the specifications are usually rather simple A sector is indicated with start and end angles in azimuth and elevation and then an RCS value is specified for that sector Often different RCS values are specified f
46. law the author has the right to be mentioned when his her work is accessed as described above and to be protected against infringement For additional information about the Link ping University Electronic Press and its procedures for publication and for assurance of document integrity please refer to its WWW home page http www ep liu se Tobias Forslow Abstract It is important for the military to know as much as possible about how easily detected their vehicles are One way among many used to detect vehicles is the use of radar sensors The radar reflecting characteristics of military vehicles are therefor often rigorously tested With measurements and simulations it is possible to calculate likely detection distances to a vehicle from different angles This process often produces very large data sets that are hard to analyze This thesis discusses and implements a method for visualizing the detection distance data set and also discusses a lot of related issues with a focus on computer graphics The main concept is called spherical displacement and the idea is to visualize the detection distances as a surface with the imagined vehicle in the center point Detection is likely inside the surface but not on the outside This concept is the next step from the colored sphere where the colors represent the detection distance which was previously used The thesis project resulted in a visualization tool that uses the new concept and can handle
47. le in wxPython and was made to work with GLEW with a few modifications 28 56 4 4 Program Comments 4 4 1 Optimizations One of the problems with the existing software was that the module that calculated the detection distances was very slow Even though there was a significant amount of calculations to be done the module was still unreasonably slow One of the first things that was done in the project was to analyze this module to find weaknesses in the design The main problem was found to be that the module was written almost entirely in core python The module does computations on large matrices and a lot of loops like the following were found if project Background Fr space for ix in range el for jx in range az Detdist ix jx 50 0 0 76 sqrt sqrt RCS ix jx Since python is not a compiled language it does not take advantage of the multitude of optimizations available in modern compilers To speed these loops up numerical python s matrix operations were used reducing the code to the following statement if self background Fr space Detdist 20 0 sqrt sqrt RCS This is in fact also a loop but it is executed in numerical python s precompiled C module which does take advantage of loop optimizations as well as other compiler optimizations Several similar loops were replaced The old preprocessor module also carried out a lot of rather slow and heavy graphical computations such as sphere generation Delaunay triang
48. n case the interpolated value lies outside data boundaries if 1 gt m_pAl1Data gt nThetaRes 1 return 0 0f if j gt m_pAllData gt nPhiRes 1 return 0 0f if i m pAllData gt nThetaRes 1 return m pAllData gt ppData i J J j if j m_pAllData gt nPhiRes 1 return m pAllData gt ppData i J j Bilinear interpolation return m pAllData gt ppData i j 1 dx 1 dy m pAllData gt ppData itl j 1 dx 1 dy m pAllData gt ppData i 3 1 1 1 dx dy m pAllData gt ppData itl j 1 dx dy 4 4 3 Sphere Generator All the meshes created by the program use the sphere generator class It creates a sphere with arbitrary resolution displaces the vertices according to the input data and triangulates the mesh The following function adds a new vertex with correct displacement depending on the scaling setting provided by the application Adds a vertex to the vertex array also adds a vertex normal since they are used to calculate the position of the vertex anyway If displacement by scalar is used the normals will need to be recalculated since the topology of the object will change void CSphere AddVertex float phi float theta Vec3f vOrigin UINT nVertex float fCurrPhi phi M PI 180 float fCurrTheta theta M PI 180 Vec3f normal Normals x is the horizontal on the screen left to right y is the vertical on the screen
49. nate system a view plane and a view volume The view point is also called the camera point or eye point and describes the viewer s position in the world space and is usually defined together with a view direction The view plane is setup normal to the viewing direction and can be seen as the screen onto which the scene later will be projected The view coordinate system is defined by the viewing direction and the view plane S er Q Figure 2 Viewing parameters Watt 2000 Figure 2 shows the different viewing parameters The first image shows a view point C with a 11 56 view direction The next image shows a view plane that is normal to the view direction The second image from the bottom shows the view coordinate system that is defined by the view direction and view plane and finally the bottom image shows the view volume as the shaded area created by the frustum of the view point the view plane and usually also a far clipping plane Watt 2000 Another operation that is carried out in view space is culling or back face elimination It compares the orientation of polygons with the view point and removes those polygons that cannot be seen This is a very simple test which will remove on average half the polygons in the scene 2 2 4 3D screen space There are two common projections used to go from 3D to 2D Parallel projection and perspective projection Parallel projection is used when the relative size of objects needs to be preserv
50. ndary Canvas The Reset Navigation Button resets all rotation and zooming in the canvases but leaves the mesh options intact To change the color of a mesh click one of the color buttons For CAD objects they will all change the color of the object For other meshes the Min Color represents the color for the smallest detection distance or RCS values and the Mean and Max Colors represents the mean and max values in the same way The colors for values in between are interpolated linearly The Min and Max Value Text boxes show the smallest and highest detection distance or RCS values for the currently selected mesh Changing these values will change the coloring of the object but not the actual geometry For example setting the Min Value to something larger than the first value will make a larger portion of the mesh use the Min Color 51 56 CAD Canvas Main Canvas Reset Navigation Mesh Objects CAD Mesh Mesh List Alpha 100 0 Specularity 100 0 1 0 Z Show on Main Canvas C Show on Secondary Canvas Show Secondary Canvas Hello Controls 1 1740310 68 53828 Create Mesh Object Dialog The Create Mesh Object Dialog is accessed with the Add button on the Options Panel It contains a Data Set List which shows all the data sets currently loaded To create a mesh first select a data set from the list set all the options or use the default options set a name for the mesh with the Mesh Label Text box and then click the
51. need to create an OpenGL canvas to render on In most labs and projects on university level this is done with the OpenGL Utility Toolkit GLUT While GLUT is simple to use it does not provide much control over the canvas it creates The canvas is coupled with a window so to use this the user interface would either have to be in a separate window or programmed in OpenGL as well None of these were an option in this project but there are other ways to create an OpenGL canvas WxWidgets and also wxPython has limited support for this Again what wx Widgets actually does is utilize the OS specific functions to create such a 26 56 canvas In the case of Windows it provides a simplified interface to Windows OpenGL WGL A nice feature of OpenGL is that once a canvas has been created all OpenGL calls will be directed to that canvas or if there are several canvases they will be directed to the currently active canvas The application uses 2 3 canvases all created by wx Widgets The main render function is located in the python module and is executed whenever wx Widgets is idle which means that the controls remain responsive The render function uses a mix of pyOpenGL calls and calls to the C rendering module PyOpenGL is a thin wrapper for OpenGL much like wxPython is a wrapper for wx Widgets Some of the graphic calls uses extensions to OpenGL These are made available by the OpenGL Extension Wrangler Library GLEW For simplicity all OpenGL calls from t
52. nt on the surface of an object Watt 2000 The most common model was developed in 1973 by Bui Tuong Phong and published in 1975 in Communications of the ACM Phong 1975 This model estimates the intensity of the light reflected from a point depending on the normal of the surface and the position of the light source and viewing directions It is called a local reflection model since it only considers direct illumination This model considers the reflected light to consist of three components I L I I Where I is the reflected light is an ambient light component is the diffuse component and I is an imperfect specular reflection component The ambient component is added to compensate for the lack of indirect illumination in the model A surface that does not have a clear view to a light source would be completely black without this component since the only light that normally would reach it is light that is reflected off other surfaces This component is usually just a constant The diffuse component is assumed to be perfect diffuse reflection which means that it reflects light equally in all directions This component is modeled as follows I I1 cos Where Z is the intensity of the incident light and 0 is the angle between the surface normal and the incident light In vector notation this becomes LEAL L N L is the light vector a vector from the light source to the point of interest is the surface normal at the point
53. ob of the fragment shader to map scalar values into colors It does this by interpolating linearly between two out of three colors A rate value between 0 and 1 is calculated from the scalar depending on the the minimum and maximum values of the scale Rate values between 0 and 0 5 will result in a mix of the minimum color and the mean color and values between 0 5 and 1 gives a mix of the mean color and the maximum color It also uses the intensity values calculated in the vertex shader and sets the alpha value dynamically from user input vec3 color float scalar scalarFrag float rate scalar scalarMin scalarMax scalarMin rate clamp rate 0 0 1 0 if rate lt 0 5 rate rate 2 0 color mix minColor meanColor rate else rate rate 0 5 2 0 color mix meanColor maxColor rate gl FragColor vec4 color Idiff Iamb Ispec specColor fAlpha 37 56 5 Results In this chapter the results of many different aspects of the project are presented It contains images from the resulting application and comparisons with the old implementation It also contains the results of the optimization tests 5 1 Spherical displacement One of the major improvements in the new version of BaseTool is the spherical displacement With spherical displacement the actual detection volume can be shown which is considerably more intuitive for the end user than the colored sphere approach The concept of spherical
54. old version 43 56 The few options that existed were accessed on a separate panel shown in figure 23 This approach was simple and sufficient for the features that the old version had Control for detection distance viewer H Detection file ONE MA Change scale l Detection file TWO Sensor information 5 Print Image M Exit 2 Back to main Figure 23 Menu of the old version In the new version the CAD model is shown in the upper left corner instead leaving much more room for the actual data visualization All the new interactive options such as transparency specularity scale and color are located beneath the CAD model on the left side The process of creating a mesh out of a data set is handled in a separate dialog The new version contains a lot of new options and features but since there are default options for almost everything it is very easy to get started The BaseTool user manual in Appendix A shows more details on how the program works and contains more screen shots Figure 24 shows the main interface of the new application 44 56 Figure 24 User interface of the new version 5 8 User manual A simple user manual was created to help the end users getting started with the application The manual contains step by step instructions for how to go from an input data set via the preprocessor module and finally displaying the visualization Apart from the getting started guide there is
55. or different frequency bands In reality such specifications can usually not be met When creating stealth vehicles the main tool is shaping the vehicle so that the radar reflection is concentrated in a few directions While there are other methods of reducing the radar signature of a vehicle such as radar absorbing materials RAMs the major contribution comes from shaping Therefore a good stealth vehicle will have heavy spikes in RCS in certain directions The application is meant to help the creators of the vehicle to prove to the client that the spikes cover a small sector and located in directions where sensors are unlikely to be located In order to do this it was decided to add modifications to the simple flat sectors mostly used These modifications are meant to give greater weight to the center of the sectors and less to the corners The first idea was to create elliptical sectors These would be useful when examining one sector at the time Section 4 4 6 describe the implementation of the elliptical sectors At a later stage in the project it was clear that this feature was unlikely to be used since it is just as easy to look at the whole data set at once rather than one sector at the time To still be able to support weighting by distance to the center of the sector a few options were added when creating these sectors in the application These options allow the user to let the RCS or detection distance value decrease with the distance from th
56. ork could be done The idea of using spherical displacement was presented to them and they decided that it was worth exploring They also wanted to see if it was possible to optimize the preprocessor module that produced the detection distances Other things on the wish list was the ability to produce high quality visualizations for marketing purposes and a way of visualizing RCS specifications There were also prerequisites on how the application should be designed and what tools to use The previous version had been created using open source tools and one requirement was that the new 7 56 version continued to use only such tools The existing version of the application used the script language python To make it easy to maintain and update the application SAAB wanted the new version to use python as well since the language was known by key individuals within the project One of the tools used in the first version was the Visualization Toolkit VTK an open source library for scientific visualization that could be controlled from python The company wanted to continue to use VTK if it was possible 8 56 2 Theory This chapter contains the background theory needed to understand the rest of the report It is divided in three parts radar computer graphics and interpolation 2 1 Radar The acronym radar stands for radio detection and ranging Radar was initially developed to replace visual target detection for several reasons Radio w
57. plication While VTK is a great tool for quickly creating scientific visualizations some of the specific features that was needed in this project were not available in VTK The OpenGL Extension Wrangler Library GLEW was used in the C module to simplify access to a few of the newer OpenGL extensions All of the tools and languages used are Open Source and more or less platform independent Even though the application was designed with Windows in mind it could easily be ported to another platform 23 56 4 Implementation This chapter goes into detail on the application design and visualization solution that was the result of the project It contains program code comments and a discussion about the rendering techniques that was chosen 4 1 Application Design The basic idea of the application design was to do all the performance sensitive calculations and rendering in C and OpenGL and use a highly flexible script language and a good widgets library for the user interface and application control This allowed for using advanced rendering techniques to speed up the application Using a script language also makes it easier to change the application later without a need to understand C or OpenGL Figure 11 Data flow Figure 11 shows the data flow for the actual test data in the application The ISAR data is read from an input file and processed by the preprocessor module This input data contains values per angle and frequency with the p
58. quency of the incoming radar signal RCS can be used to calculate detection distances for different radar threats The detection distances are much more intuitive than SAR images and can thus if visualized in a good way be used as information to fighter pilots and other military personnel without a need to understand the underlying physics 2 1 2 Inverse Synthetic Aperture Radar Synthetic Aperture Radar SAR and Inverse Synthetic Aperture Radar ISAR are two commonly used radar modes that can be used for mapping Any time two objects have relative rotation to one another a SAR map can be formed in the plane of rotation Lynch 2004 In ISAR the object that is mapped is rotated and the radar is stationary rather than the other way around This is a method used under controlled forms for measurements of radar reflection properties of aircraft and other vehicles 2 1 3 Stealth A stealth vehicle is often thought upon as a vehicle that is nearly invisible to radar but making a vehicle invisible to radar is called radar signature control and is just a part of the much larger concept of stealth Stealth is not a single concept but an assemblage of techniques which makes a system harder to 9 56 find and attack Included in this concept is controlling emissions like heat sound exhaust fumes communications radar et cetera and also everything that requires external illumination of some kind like magnetic and gravitational anomalies re
59. results 5 6 Optimizations The optimizations described in section 4 4 1 were tested with different data sets to find the performance gain The time to run the preprocessor module and get show the result on screen was tested and the times for the preprocessor and preparations to show the data was also noted These tests were carried out on a 1 7 GHz Pentium 4 with 1 GB of RAM 41 56 Test Calculation time Loading time Total time GR2 full old 1 hr 40 min 11 sec 45 sec 1 hr 40 min 56 sec implementation GR2 small old 1 min 58 sec 5 sec 2 min 3 sec implementation Thin metal plate old 39 sec 4 sec 44 sec implementation GR2 full new 22 sec 8 sec 30 sec implementation GR2 small new lt 1 sec lt l sec sec implementation Thin metal plate new lt l sec lt l sec lt l sec implementation Table 2 Optimization tests Table 2 shows execution times for three different data sets with the old and new implementation GR2 full is the data set shown on most of the images in the report GR2 small is a narrow band of the full GR2 set and is about 50 times smaller The thin metal plate set is a very small set which should be executed nearly instantly and therefore is good for testing how much overhead the two implementations have It should be noted that the two implementations do not perform the exact same tasks In particular the old implementation does Delaunay triangulation which isn t needed in the new ver
60. roduced in 1971 be Henri Gouraud Gouraud 1971 Better results can be achieved through different weighting schemes One idea is to weight the face normals by the angle under which a face is incident to a vertex Figure 7 shows the concept the normal 4 is weighted by the angle amp when added to the vertex normal for the center vertex This algorithm was proposed by Th rmer and Wiitrich in 1998 Th rmer et al 1998 Another idea first proposed by Max in 1999 Max 1999 is to weight each face normal with the area of the face Figure 7 Weighting by angle Both the weight by area and the weight by angle methods works well for smooth objects but when it comes to objects with edges there will be ugly artefacts A problem when generating vertex normals is that not all objects in reality are smooth In particular it is hard to preserve edges when using Phong or Gouraud shading For an edge to look good it needs two normals one for each side of the edge and the normal models does not take this into account When modeling new meshes the designer is usually given the option of making an edge hard In practice this means duplicating the vertices on the edge and using one vertex normal per vertex This makes it possible for the surface to have two vertex normals at the same position which can account for the discontinuity of the edge If the vertex normals are generated we need a way of detecting edges and then splitting the vertices accordingly One
61. same direction as the camera it only causes annoying glare coloring the sphere white in the position where the user is most likely to be looking Figure 18 shows the specular glare corrupting the color information on a colored sphere Figure 18 Specular effects on a colored sphere Another example of an object that should use no or low specularity is the specification sets These are often spherical or at least partly spherical and are usually used with transparency It s easier to see through the object if the specularity is low Because of this problem the user can control the specularity of all object by setting a value between 0 and 100 with a slider 5 4 Downsampling data The data sets that this application is meant for are very diverse Some contain huge amounts of data and even though the application could handle showing several million triangles on the test computer there is a possibility that the application will be run on a less advanced machine Being able to 39 56 change the resolution of the data before visualization can help ease the load on the hardware Figure 19 shows the same data set with different resolutions The top image contains 518 400 triangles and the bottom image contains 129 600 The difference is barely visible in these images but is a lot easier to detect in the application itself Naturally some of the small details are lost but the main features seem to remain untouched Increasing the resolution above that of t
62. sion and the new version does a lot more sophisticated vertex normal calculations For large data sets the new implementation is about 200 times faster than the old one in total It is also about 5 6 times faster in just loading the precalculated data and showing it on screen even though it does significantly more advanced computations in this step 5 7 Showing elliptical sectors The idea behind using elliptical sectors and the implementation is discussed in section 4 4 6 In the end the usefulness of this feature in the context of radar visualizations could be questioned But it was implemented and is still a part of the application As can be seen in figure 21 the edge vertices are located on the edge of the ellipse itself making the shape look good A few of the triangles break away from the general pattern Interpolating the vertex positions in one more dimension would probably solve that problem 42 56 Figure 21 Elliptical sector in wireframe mode 5 8 User interface As figure 22 shows the old version of the application was rather simple Being simple it was also easy to use The user just had to open a file and the CAD model and sphere was shown on screen A problem with the old user interface was that much of the screen was wasted by showing the CAD on half the screen A nice detail was the color bar on the right showing how to interpret the colors File GR2_whole_sphere_P590_Damping h5 Figure 22 Visualization window of the
63. tor of the sphere data it can sometimes be interesting to disregard the corners of the sector To help with this the application can create sectors of elliptical shape These are created by sampling the data in a grid ignoring points that lie outside the imagined ellipse moving certain points to the edge of the ellipse and interpolating needs correct values for the new points The following code sample finds the new position for points that are near the edge of the ellipse It is based on the marching cubes algorithm Lorensen and Cline 1987 but is ported to the 2D case marching squares and somewhat simplified since ellipses are convex objects Grid s close ampling of an ellipse Moves points that are outside the edge but to it to the perimiter itself Does nothing with values that are insid th llipse or way outside it To find out if x y is outside th llipse but near th dge the funct checks x y yStep are inside th llips if the neighbours x xStep y x xStep y x ytyStep and tion bool CDataArray FindNewPosition float amp x float amp y float xStep float yStep float a fy if boo boo boo boo a float b If the coordinates are inside th llipse use them as they are IsInsideEllipse x y a b return true l bLeftInside IsInsideEllipse 1 bRightInside IsInsideEllipse l bAbovelnside IsInsideEllipse 1 bB
64. ts Therefor the triangulation can be solved in a simple double loop Four corners of a quad UINT pl p2 p3 p4 Triangulation counter clockwise ordering for i 0 i lt m nThetaRes 1 i for UINT 3 0 3j lt m _nPhiRes 1 3 pl i m _nPhiRes _ vIndices _ vIndices vIndices vIndices _ vIndices p2 p1 1 p3 p1 m _nPhiRes p4 p3 1 m_pMesh gt m m pMesh gt m m_pMesh gt m m_pMesh gt m m_pMesh gt m m pMesh gt m 31 56 vIndices pus pus pus pus pus pus Bottom left Bottom right Top left Top right h back p1 h back p4 h back p3 h back p1 h back p2 h back p4 4 4 4 Vertex Normals with Edge Preservation The use of edge preservation is motivated in section 4 2 and the idea behind it is described in section 2 5 8 in The following code shows somewhat simplified how vertices can be split using this algorithm Before this code is executed face normals and angles are calculated The vector vVertexInformation contains links to all faces that the vertex belongs to as well as the corresponding angle The algorithm calculates the dot product between normals of the first two faces in the list If the value is larger than the cosine of the crease angle it splits the vertex Otherwise the normals are added and weighted by their corresponding angles When an edge is found a new vertex is created for all the following
65. ulation and normal generation Some of these were done in python and were slow because of that others like Delaunay triangulation was done in VTK C modules but are still heavy Sphere mesh and normal generation were moved to the new C visualization and some other features were removed altogether since they were no longer needed with the new implementation 4 4 2 Interpolation The ability to interpolate freely across the data was important to allow the user to change the resolution in phi and theta In this way it is possible to control the complexity of the calculations The method used for the interpolation was simple bilinear interpolation A function that returns an interpolated value for any given phi and theta was created Takes values in spherical coordinates and returns interpolated values float CDataArray GetInterpolatedValue float theta float phi calculate decimal indices float x theta m pAllData gt fThetaStep m pAllData gt nThetaOffset float y phi m pAllData gt fPhiStep m pAllData gt nPhiOffset Calculate indices int i int x int j int y Get the offset float dx fabsf x 1 float dy hh y o 1 hh Ke I u 29 56 recalculate indices for angles outside the boundaries of the array really only works for phi int phiRes int m pAllData gt nPhiRes if not done will break if 3 lt 0 j phiRes abs j phiRes 1 else J 3 phiRes 1 clamp i
66. using bilinear interpolation To achieve different values at each vertex special normals called vertex normals are used See section 2 2 8 for details on vertex normals The big problem with this method is its inability to correctly handle highlights Since the intensity values are only calculated in the vertices the algorithm will miss highlights that should have appeared somewhere on the polygon Watt 2000 15 56 2 2 7 Phong shading A polygon mesh is often an approximation of a smooth surface and as such the normal of the surface should vary across the polygons Phong shading Phong 1975 is a way of dealing with this problem by interpolating vertex normals across a polygon rather than just interpolating the intensity This solves the problems with the highlights and makes it possible to get a smooth look to objects that in reality are made up of polygons Using Phong shading is considerably more expensive in terms of computations but in modern hardware it is not very likely to become the bottleneck since most hardware is built to use this method Watt 2000 2 2 8 Generating vertex normals Phong and Gouraud shading use vertex normals to estimate the curvature of the surface These normals are usually calculated as the average of the normals of all the faces that the vertex belongs to N N N N N Simply averaging the normals of the adjacent faces sometimes create problems since all faces are weighted equally This method was int
67. ution Such images could be used in marketing Some or all of these features will be implemented during the summer Further testing of the user interface and the application features themselves should be carried out Adjusting the user interface with the help of such tests should be fairly easy thanks to the use of python and wx Widgets Even though the bilinear interpolation currently implemented in the application seems to be sufficiently accurate it would be interesting to try using bi cubic spline interpolation or some other more advanced interpolation technique instead 47 56 References Knott et al 1993 Eugene F Knott John F Schaeffer Michael T Tuley Radar Cross Section Artech House Inc Norwood MA USA 1993 ISBN 0 89006 618 3 Lynch 2004 David Lynch Jr Introduction to RF Stealth SciTech Publishing Inc Raleigh NC USA 2004 ISBN 1 891121 21 9 Watt 2000 Alan Watt 3D Computer Graphics Third Edition Pearson Education Limited Essex England 2000 ISBN 0 201 39855 9 Phong 1975 Bui Tuong Phong Illumination for Computer Generated Images Communications of the ACM Vol 18 6 311 317 June 1975 Gouraud 1971 H Gouraud Continuous shading of curved surfaces IEEE Transactions on Computers 20 6 623 628 1971 Robins 1997 Nate Robins Smooth Normal Generation with Preservation of Edges http www xmission com nate smooth html Scientific Visualization Project at University of Utah Catmull 19
68. ver be exceeded for the set 54 56 Create Mesh Object Date Set Metro Specification Data Set Phi Start Phi Stop 0 360 721 Theta Kart ng hon Theta Samples 90 90 181 Data Set Label Specification Data Set Specification Data Specification Sector Dialog To add more information to the specification set select it from the Data Set List and click the Add Sector To Set Button in the Create Mesh Object Dialog You can chose from several different types of sectors to add The sector type controls how the value varies over the sector according to the following table Sector Type Value Flat min Linear min max min x ly 2 Elliptical min max min x p y p 2 Gaussian min max min e 1 2 x 0 4 p y 0 4 p In practice this means that the Flat Sector mode gives a constant value across the sector The Linear mode gives linearly diminishing values For the Elliptical mode values will be close to the min value for most of the sector but near the max value in the corners The p or Power To parameter controls how fast the values diminish a higher Power To means most of the sector will be close to the min value The Gaussian mode is mostly for testing purposes and should not be used for any real projects For each of the modes except the F at mode you can chose to let the values diminish in phi only theta only or both angles The data set created like this can then be used in making a new M
69. vertices This may split an unnecessarily large amount of vertices but simplifies the algorithm somewhat for i 0 i lt m_nVertices i t if vVertexInformation i bIsUsed continue vector lt UINT gt faces vVertexInformation i vFaces vector lt float gt angles vVertexInformation i vAngles Vec3f normal 0 0f 0 0f 0 0f normal 0 vFaceNormals faces 0 0 normal 1 vFaceNormals faces 0 1 normal 2 vFaceNormals faces 0 2 bool bSplit false for UINT j 1 3 lt faces size j UINT face faces j NormalizeVec3 normal float dot Vec3fDot vFaceNormals face normal 1f bSplit dot lt cosf m_fCreaseAngle bSplit true if bSplit UINT v1 m vindices face 3 UINT v2 m vindices face 3 1 UINT v3 m vindices face 3 2 UINT id 0 UINT vert if i v1 id face 3 vert v1 else if 1 v2 id face 3 1 vert v2 else if 1 v3 id face 3 2 vert v3 if id 0 m_vindices id nVertices m_vVertexNormals push_ back vFaceNormals face m vVertices push back m vVertices vert nVertices 32 56 else normal 0 vFaceNormals face 0 angles j normal 1 vFaceNormals face 1 angles j normal 2 vFaceNormals face 2 angles j NormalizeVec3 normal m vVertexNormals i normal 4 4 5 Specification Sectors One new feature in the application was the ability to show specification sectors T

Download Pdf Manuals

Related Search

Related Contents

Art.-Nr. SF-1670  Appareils à moteurs  LA PRISE DE RISQ}JES DANS LES RELATIONS SEXUELLES  emc ou encephalomyocardite du porc editorial  evaluation des risques remote drill rig  Honeywell Hpa-050 User's Manual    User`s Manual  

Copyright © All rights reserved. Failed to retrieve file