OS Terrain 5 - Digimap Home Page
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1. 7 Computer hardware E M 7 Computer SOftWAre eerie tte t inn nene Ib ned era La e Ux ERA deaaveaaacen REX R Nn Aaaa 7 ruri EL es e aaran er a aaaea aiaa aE EETA NE 8 fnm 8 troduction T a aiana 8 Mean high and low water representation in grid 8 enit 8 agere oio OH E 8 gulrBiqo cm E R 9 Mean high and low water representation in contours esseeen en 9 Sese TE 9 Data metadata and additional files eeeeeeeeeeeeeeeee eese eeee eene nennen nnne nnn 10 Metadata H 10 Metadata viewing style sheet eene enne 11 OS Terrain 5 source data 5 niece iesas tne ereo tau n kar Sr e REESE IRRuAS RE ENEE RETE RRR RARE isadora adepi ERR 13 nurere i Te ope 13 luco c 13 Data revision P E EE 13 Positional accuracy requirements eene 14 Modelling of features in source data sssssssseeen emen 14 Conformance 15 The National Grid oen eee cece nats pects cee MR Pe MA ad EEUU RR EEUU eee 17 Product and service performance report form cccceeeeeseeeceeeeeeeeeeeeneeeeeeeeseeeeeeneeeeeees 18 v1 1 07 2013 D05300 50 OS Ter2. gmd code gmx Anchor xlink href urn ogce def crs EPSG 27700 gt British National Grid lt gmx Anchor gt rr OS Terrain 5 user guide chapter 3 v1 1 07 2013 Crown copyright Page 11 of 32 Metadata xml file referencing the XSLT viewing style sheet example This is the same section of the metadata file above when viewed directly by clicking on the file thus utilising the style sheet OS Terrain Tile Metadata Product identification Product name OS Terrain 5 Spatial representation grid Tile reference NT23NE Topic category elevation Coordinate reference systems British National Grid Esri grid styling asc aux xml file This XML file contains min max mean and standard deviation height values for the product in a format defined by Esri The same values are supplied for every tile Providing these height statistics is intended to allow colour ramps to be applied by the user such that adjacent tiles are styled consistently This can be disabled by moving the asc aux xml file from each downloaded zip file or adjusting the parameters of the minimum and maximum heights in a GIS if desired NENNEN OS Terrain 5 user guide chapter 3 v1 1 07 2013 Crown copyright Page 12 of 32 Chapter4 OS Terrain 5 source data Introduction The source DTM for OS Terrain products is captured as a triangulated irregular network TIN by editing with mass points
3. normally exclude ground surface features such as buildings woodland and so on eastings See rectangular coordinates edgematch The process of ensuring that data along the adjacent edges of blocks of data matches in both positional and attribute terms EPSG code The EPSG Geodetic Parameter Dataset is a structured dataset of Coordinate Reference Systems and Coordinate Transformations In the dataset each Coordinate Reference System has its own unique code number It was created by the European Petroleum Survey Group and is maintained by the Geodesy Subcommittee of OGP International Association of Oil and Gas Producers feature An item of detail within a digital map that can be represented by a point symbol text or line feature identifier A unique code to identify an individual feature A specified part of a record containing a unit of data such as the date of digitising The unit of data may be a data element or a data item OS Terrain 5 technical specification annexe A v1 1 07 2013 Crown copyright Page 30 of 32 field A specified part of a data file containing a unit of data such as the date of flying format The specified arrangement of data in a file geographical information system GIS A system for capturing storing checking integrating analysing and displaying data that is spatially referenced to the Earth This is normally considered to involve a spatially referenced computer database and appropriate appl
4. sucre aito nid iL Me Ut LL Mi ME TI UI LUPA D Mtr E Quotation or order reference ws isd ns d oc p ore totae e edades epa idee da Du ed nce Eod Le eod eu dee a da queo EA oed e Mni Please record your comments or feedback in the space below We will acknowledge receipt of your form within three 3 working days and provide you with a full reply or a status report within 21 working days If you are posting this form please send it to OS Terrain 5 Product Manager Ordnance Survey Adanac Drive SOUTHAMPTON SO16 OAS If you wish to return it by fax please dial 023 8005 6159 Any personal information that you supply with this report form will be used by Ordnance Survey only in the improvement of its products and services It will not be made available to third parties OS Terrain 5 user guide annexe A v1 1 07 2013 Crown copyright Page 18 of 32 OS Terrain 5 Technical specification Contents Section Introduction Chapter 1 Chapter 2 Chapter 3 Chapter 4 Annexe A Page no 20 Purpose of this specification and disclaimer sssssssssssseeeeeee 20 Copyright in this specification sssri EEE SE R 20 Technical specification introduction c ccceeeeeeeeeeeeeeeeeeeeeeeeeeneeeeseeeseeeseaneeseeeeneeeseeanes 21 ASCII grid for OS Terrain 5 Qrid cicccccccccccccccctesscecesccececsecterecscctecesdecettecacccstenssc
5. National Grid coordinates of the same point on the ground As the true position can never be known exactly the statistic is quoted relative to the best known position determined by precise survey methods accuracy The closeness of the results of observations computations or estimates to the true values or the values accepted as being true Accuracy relates to the exactness of the result and is a measure of the exactness of the operation by which the result is obtained ASCII American Standard Code for Information Interchange a standard binary coding system used to represent characters within a computer bit An acronym for binary digit breakline A line indicating discontinuity in a terrain surface that is an abrupt change in gradient byte A unit of computer storage of binary data usually comprising 8 bits equivalent to a character Hence megabyte one million bytes and gigabyte one thousand million bytes character A distinctive mark an inscribed letter one of a set of writing symbols contour A line connecting points of equal elevation coordinates Pairs of numbers expressing horizontal distances along orthogonal axes Alternatively triplets of numbers measuring horizontal and vertical distances copyright Copyright is a legal property right that enables the creator of an original work to protect it from unauthorised use Through the Copyright Designs and Patents Act 1988 Crown copyright continues to subsist in
6. all Ordnance Survey products until the end of the period of 50 years from the end of the year in which they were published and in the case of data from the end of the year in which it was extracted from the Ordnance Survey database Crown copyright is vested in The Controller of Her Majesty s Stationery Office who has delegated powers to the Director General Ordnance Survey for the administration of copyright in publications and data including the determination of the rules and terms under which permission for their reproduction is given currency An expression of the currency of the data that is when the real world change was identified and represented in the data data A representation of facts concepts or instructions in a formalised manner suitable for communication interpretation or processing data capture The encoding of data In the context of digital mapping this includes map digitising direct recording by electronic survey instruments and the encoding of text and attributes by whatever means OS Terrain 5 technical specification annexe A v1 1 07 2013 Crown copyright Page 29 of 32 data format A specification that defines the order in which data is stored or a description of the way data is held in a file or record data model An abstraction of the real world which incorporates only those properties thought to be relevant to the application or applications at hand A data model would normally define specific
7. associated parts of the guide and to relevant Internet resources by clicking on the blue hyperlinks and the table of contents If you are unfamiliar with any words or terms used and require clarification please refer to the glossary at the end of the document C OS Terrain 5 user guide preface v1 1 07 2013 Crown copyright Page 4 of 32 Chapter1 Introduction Using this guide This document consists of e auser guide which contains basic information you will need to understand use and manage OS Terrain 5 and e atechnical specification which contains detailed technical information about the data formats We endeavour to provide the best customer experience and we value your feedback Annexe A in the user guide contains a product and service performance report form for you to submit any comments on OS Terrain 5 You may also email us at customerservices ordnancesurvey co uk More information including FAQs and updates are available on our web pages http www ordnancesurvey co uk oswebsite products os terrain 5 index html OS Terrain overview OS Terrain is the name given to Ordnance Survey s new range of height products These are three dimensional models of the bare earth surface known as digital terrain models DTMs The range currently consists of e OS Terrain 5 a mid resolution DTM designed to be interoperable with our large scale data and e OS Terrain 50 a lower resolution DTM product designed for landscape v
8. facilities are available varying from tablets or computers using GIS or computer aided design CAD to mainframe computers with specialised translators and applications Please see Coverage and file sizes for more information Your system supplier will be able to advise on your requirements Computer software OS Terrain 5 is supplied as inert data in a variety of formats and does not include software for data manipulation GML is an open standard format and the data may need to be translated into the appropriate format for use within a GIS application A wide range of GIS software can read the GML contour data without translation MEER OS Terrain 5 user guide chapter 1 v1 1 07 2013 Crown copyright Page 7 of 32 Chapter 2 OS Terrain 5 This chapter describes the structure of the data in grid and contour forms Grid In the above image the OS Terrain 5 grid has been shaded in a GIS Introduction The height data is presented as a raster dataset of height values which are calculated at the centre of the pixel This method of creating the data means there are no overlaps between tiles nor common values along the edge Coordinate reference systems for DTMs may be used to calculate the DTM origin and coordinates of individual posts Mean high and low water representation in grid Due to local tidal conditions the height of the mean high and low water mark varies continuously around t
9. is a subset of the full GML specification intended to make it easier for GIS vendors to provide a minimum level of support for GML GML schema XML schemas are used to validate the format and content of the GML The GML specification provides a set of schemas that define the GML feature constructs and geometric types These are designed to be used as a basis for building application specific schemas which define the data content The OS Terrain 5 application schemas which are referenced by the data are available at http www ordnancesurvey co uk The user may need to be connected to the Internet to access these online schemas while working with OS Terrain 5 in GML unless their software supports local copies of the schema Depending upon the Software that is being used to read the data the user has the following options e The software does not use the schema therefore does not need to be connected to the Internet e The software needs the schema but can reference it from a local copy if it is downloaded in advance e The software needs the schema and can only reference it from the online version therefore needs to be connected to the Internet Feature types The model is feature based so that ContourLine SpotHeight and LandWaterBoundary are feature types with specific attributes Please see GML contours and spot heights for more information Coordinate reference system The coordinate reference system for geometries in th
10. os SpotHeight gt lt os member gt Example of the LandWaterBoundary feature types lt os member gt lt os LandWaterBoundary gml id os t5 sx98se 17 lt os geometry gt lt gml LineString srsName urn ogc def crs EPSG 27700 gml id os t5 sx98se 17 geom gml posList 297786 59 81469 64 297783 26 81469 75 297783 26 81466 75 297786 59 81469 64 gml posList gml LineString os geometry lt os propertyValue uom m gt 1 62 lt os propertyValue gt lt os waterLevelCategory gt meanHighWater lt os waterLevelCategory gt lt os LandWaterBoundary gt lt os member gt _ i ee AL CLEC LAL CN TT OS Terrain 5 technical specification chapter 3 v1 1 07 2013 Crown copyright Page 26 of 32 Chapter 4 Esri shapefile for OS Terrain 5 contours Esri shapefile overview The Esri shapefiles consist of eight separate files for the point and line features Detailed shapefile model Object ESRI Classes Feature Shape esriFieldTypeGeometry OSTerrainFeature ID esriFieldTypeString FEAT TYPE esriFieldTypeString SUB TYPE esriFieldTypeString PROP VALUE esriFieldTypeSingle File name Description Examples Contour line files tile Shape format name line shp The contour geometry tile Shape attribute ID FEAT TYPE SUB TYPE PROP VALUE name gt _line dbf format os t5 sy09ne 113 ContourLine master 25 00 A database file that contains the os t5 sy09ne 114 Contour
11. progressing at 5 m intervals to the east The header provides the coordinates of the south west corner xllcorner and yllcorner to ensure that a GIS places the data correctly Number of points ncols 1000 nrows 1000 xllcorner 295000 example yllcorner 85000 example cellsize 5 21 72 21 82 21 91 22 01 22 07 22 13 22 19 Data section The height values are presented in the standard ASCII grid format as a series of real values The height values are given to the nearest 0 01 metre OS Terrain 5 technical specification chapter 2 v1 1 07 2013 Crown copyright Page 22 of 32 Chapter 3 GML for OS Terrain 5 grid and contours This chapter describes how OS Terrain 5 is defined in GML version 3 2 1 An understanding of XML and XML schema is required GML overview The OpenGIS GML encoding standard the GML is an XML grammar for expressing geographic features GML serves as a modelling language for geographic systems as well as an open interchange format for geographic transactions on the Internet As with most XML based grammars there are two parts to the grammar the schema that describes the document and the instance document that contains the actual data A GML document is described using a GML schema This allows users and developers to describe generic geographic datasets that contain points lines and polygons http www opengeospatial org standards gml The GML conforms to GML 3 2 1 simple features level 0 which
12. the data but allows you to apply your own choice of colour ramp Metadata tile name gt xml A metadata file for grid data providing information on the flying date and so on Contour data GML tile name gt gml GML data file Metadata tile name gt xml A metadata file for contour data providing information on the flying date and so on Contour data Esri shapefile tile name line shp Esri shapefiles for contour and tideline data tile name line dbf tile name line shx tile name line prj tile name point shp Esri shapefiles for spot height data tile name point dbf tile name point shx tile name point prj Metadata tile name gt xml A metadata file for contour data providing information on the flying date and so on Metadata The XML metadata for the new terrain products follows the GEMINI metadata standard which Ordnance Survey has committed to for the UK Location Programme and INSPIRE Ordnance Survey has provided metadata for national sets of products www ordnancesurvey co uk oswebsite xml products OS Terrain 5 will also have metadata in this form on a per tile basis The XML metadata contains comments to clarify the meaning of the XML tags used in the file Name Description XML Product identification Product name OS Terrain 5 gmd MD DataIdentification gmd citation gmd CI C itation gmd collectiveTitle gco CharacterString Spatial
13. you and your organisation are contained in the customer contract made between you and Ordnance Survey If there is an inconsistency between the terms of your customer contract and this guide then the terms of your customer contract prevail If you or your organisation has not signed a valid current customer contract then you are not entitled to use the product Purpose and disclaimer This guide is provided for guidance only and does not constitute any warranty representation undertaking commitment or obligation express or implied about the product or its suitability for any particular or intended purpose Any warranties representations undertakings commitments and obligations given by Ordnance Survey about the product and or its suitability for any particular or intended purpose are set out in your customer contract It is your responsibility to ensure that this product is suitable for your intended purpose Ordnance Survey does not accept any liability whether for breach of contract negligence or otherwise for any loss or liability you or any third party may suffer in relying on this guide and any guidance suggestion advice or explanation provided in it Any liability that Ordnance Survey has to you in relation to the product its supply use accuracy data supplied functionality or any other liability arising out of or in connection with the product is limited as set out in your customer contract We may change the information in t
14. Line ordinary 05 00 attributes of each os t5 sy09ne 115 ContourLine ordinary 70 00 feature tile Shape index format name line shx A positional index of the features to enable searching tile name line prj Projection format PROJCS British National Grid GCEOGCS GCS OSGB 1936 DATUM Coordinate reference system information OS Terrain 5 technical specification chapter 4 v1 1 07 2013 Crown copyright Page 27 of 32 Spot height files lt tile name gt _point shp lt tile name gt _point dbf Shape format The spot height geometry Shape attribute format A database file that contains the attributes of each feature ID os t5 syO9nw 0 os t5 syO9nw 1 os t5 sy09nw 2 FEAT TYPE SpotHeight SpotHeight SpotHeight SUB TYPE generic generic generic PROP VALUE 31 00 22 00 15 00 tile name point shx Shape index format A positional index of the features to enable searching tile name point prj Projection format Coordinate reference system information PROJCS British National Grid GEOGCS GCS OSGB 1936 DATUM OS Terrain 5 technical specification chapter 4 v1 1 07 2013 Crown copyright Page 28 of 32 AnnexeA Glossary For detailed general information about mapping please visit our support pages online absolute accuracy A measure that indicates how closely the coordinates of a point in Ordnance Survey map data agree with the true
15. The structure of the data either gmd MD DataIdentification gmd spatialRepresent i i ionT MD ialR ionT representation grid DTM or vector contours VECUBNUSND Sp tialRepresontationiyp code Tile reference 5 km National Grid tile reference 9md MD_DataIdentification gmd citation gmd CI_ Citation gmd title gco CharacterString Topic category INSPIRE theme elevation gmd MD DataIdentification gmd topicCategory gm d MD TopicCategoryCode Coordinate The projected coordinate gmd MD ReferenceSystem gmd referenceSystemIden reference reference system British tifier gmd RS Identifier gmd code gmx Anchor i y xlink href urn ogc def crs EPSG 27700 Briti systems National Grid and the vertical sh National Grid reference system Ordnance Datum Newlyn gmd MD ReferenceSystem gmd referenceSystemIden tifier gmd RS Identifier gmd code gmx Anchor xlink href urn ogc def crs EPSG 5701 Ordnan ce Datum Newlyn ID LLL w c M M M i OS Terrain 5 user guide chapter 3 v1 1 07 2013 Crown copyright Page 10 of 32 Name Description XML Change history Flying date s The date that the area was flown m enone rer E pn ns by Ordnance Survey for revision oo anani rione oa S P Temporsitae To accommodate multiple flying dates within the tile two values will be recorded earliest flying date then latest flying date present Both dates can be identical Fo
16. ame height as the contour it will be removed It is possible that some spot heights could be lower than the surrounding contour due to genuine depressions The z value is rounded to one decimal place GML feature types The feature types within the contours enable their representation as individual features to enable easier interpretation for example the contours can be drawn as different colours to highlight the index contours the high water mark and spot heights over a certain value The contours and tidelines have been rounded to two decimal places The column names have been reformatted to facilitate compliance with Esri software OS Terrain 5 technical specification chapter 3 v1 1 07 2013 Crown copyright Page 24 of 32 ContourLine geometry GM_LineString The structure of the feature propertyValue Distance The length of the contour contourLineT ype String master ordinary auxiliary Notes The ContourLine sub type value names align with INSPIRE draft elevation specification The terms master and ordinary represent the more traditionally recognised terms index and standard contours respectively SpotHeight geometry GM_Point The structure of the feature propertyValue Distance The z value height above Newlyn or other British height datum of the feature spotHeightType String formSpot generic mountainPass summit Notes At launch only the sub type value generic has been used but
17. and breaklines and or automated techniques within a photogrammetric environment The TIN is a superior model for three dimensional data as it uses triangles which can retain the edges of features more accurately than a grid for example The source data capture is subject to demanding rules defined by the height capture specification Particular attention is paid to communication routes and features significant to height applications This section describes some of the key capture requirements from the detailed capture specification that we endeavour to achieve in the source data The grid and contour products are both interpolated from this source TIN model Coverage The minimum coverage of the data extends out to the low water mark defined by Hydrographic Office tables with a height value for each 5 km by 5 km tile For England and Wales the low water mark is mean low water MLW and for Scotland mean low water springs MLW S All land wholly within inland water bodies that is represented by topographic area features is captured according to the positional accuracy requirements of the area The minimum requirement is to capture the outer edge of the feature The surrounding water will remain flat Any other land within inland water bodies captured by automated processes will be removed from the data Data revision Height data will be updated as part of the integrated capture programme alongside our large scale data revision In
18. areas that have already been modelled update is only required when real world change has occurred for example a new motorway cutting MEN OS Terrain 5 user guide chapter 4 v1 1 07 2013 Crown copyright Page 13 of 32 Positional accuracy requirements The z values of the source TIN data have to meet positional accuracy requirements according to their geographic location The terrain has been divided into three classifications urban and major communication routes rural and mountain and moorland to ensure that modelling reflects customer requirements The accuracy of the height value above Ordnance Datum Newlyn must achieve the RMSE set for each area which are not the same as the stated product accuracy Modelling of features in source data Representation of the surface The height of the bare earth surface is recorded as a series of points with three dimensional coordinates The X and Y coordinates are eastings and northings in OSGB36 the Z coordinate is height in metres relative to the datum for the area The vast majority of areas will record a height relative to Ordnance Datum Newlyn For a small number of offshore islands a local datum has been used The bare earth surface excludes buildings supported structures and vegetation Structures that form an obstruction at ground level such as dams breakwaters and groynes wide enough to affect the positional accuracy requiremen
19. ch as points lines and polygons to enable spatial analysis A shapefile consists of a number of files designed to hold information essential for the transfer of this data between software products that are capable of reading shapefiles spot height A point on the Earth s surface for which the height above a reference datum is known and which has been fixed by observation transfer format The format used to transfer data consistently between computer systems In general usage this can refer not only to the organisation of data but also to the associated information such as attribute codes which are required in order to successfully complete the transfer triangulated irregular network TIN This is a vector data structure that represents a surface in three dimensions Mass points or z values are joined up as irregular triangles to form a surface to provide a more accurate and less dense method of representing a digital terrain model This is because the edges of features are preserved and mass points are only depicted where necessary to depict changes in slope URN Uniform Resource Name is a type of uniform resource identifier URI which was developed in the early stages of the Internet to strengthen the links between documents by providing a registered namespace Extensible Markup Language XML This is a markup language written in a textual data format designed to encode documents and data structures for transfer over the Internet I
20. cttecsscerteessterse 22 pwrescKeu ln 22 BEESqUeU lE 22 Header Section sses ERRRA RE MERE aa aaa a aun cnanedenaderedaa QUEE MEINER RM E RAUS 22 Number of points viciceicnter 22 BEEN A 22 GML for OS Terrain 5 grid and contours eese eene nnne 23 eumoT iim Ai 23 euntem M 23 Feature ypES e 23 GML grid for OS Terrain 5 uiii sente trece eser ete eben Las deeds rn Eu R D wed a inna 24 GML contours and spot heights for OS Terrain 5 sssssssssseee een 24 arcere 24 Spot lielghts 3 iiie dera te Deed a ide ree edes d edad edv eee Ta v aad rer t depre x 24 GME feature types i e tado eet a He e LE Re ep ete anale ge eee dac 24 Esri shapefile for OS Terrain 5 contours eeeeeseseeseseeeeeeeeeeen nne nnne 27 Esi shapeftle OVerVIGW cs ttt ca tt t RR RR TOV KE CA RABIA DIN ECL E RARAQIN RA TEX RR A TRAN REA AR 27 Detailed shapefile model sse mener nnne 27 Ee a L E E E E A E S a A A E EET 29 v1 1 07 2013 OS Terrain 5 technical specification contents v1 1 07 2013 Crown copyright Page 19 of 32 Introduction Purpose of this specification and disclaimer This is the technical specification hereafter referred to as the specification a
21. dates e specific modelling of significant features particularly networks e available in a variety of formats e full coverage of Great Britain e designed to work with Ordnance Survey s large scale data e supplied as both grid and contours with spot heights e quarterly product updates e based on the draft Infrastructure for Spatial Data in Europe INSPIRE elevation specification and e available in geography markup language GML 3 2 using Open Geospatial Consortium OGC simple features profile level 0 Accuracy OS Terrain 5 has been measured against with GPS points in a range of sample areas to provide a root mean square error RMSE value for the height points in each geographic area urban and major communication routes rural and mountain and moorland The location of these areas will be available on the OS Terrain 5 web page at http www ordnancesurvey co uk oswebsite products os terrain 5 index html Urban and major communication routes 1 5 metres RMSE Rural 2 5 metres RMSE Mountain and moorland 2 5 metres RMSE Root mean square error This is the average of the mean heights collected in a sample area The accuracy will be at its highest on modelled features such as roads and lakes Supply format OS Terrain 5 is available as e 5 metre grid in ASCII grid and GML 3 2 1 simple features profile level 0 and e 5 metre contours and spot heights in Esri shapefile or GML 3 2 1 simple features profile lev
22. dates of the product See the latest coverage map on the OS Terrain 5 web page at http www ordnancesurvey co uk oswebsite products os terrain 5 index html E OS Terrain 5 user guide chapter 1 v1 1 07 2013 Crown copyright Page 6 of 32 Data will be compressed using the zip compression method and is not encrypted Compression rates vary for contour tiles dependant on the number of features in the geographic location A full national supply of OS Terrain 5 is approximately Grid 6 6 Gb compressed Contours GML 1 4 Gb compressed Contours shapefile 1 2 Gb compressed INSPIRE compliance OS Terrain 5 is designed to be INSPIRE ready Ordnance Survey is a leading member of the UK Location Programme which is charged with delivering INSPIRE a directive that applies to all member states and aims to enable more joined up data across public bodies for environmental applications At the time of OS Terrain product development the INSPIRE elevation specification had not been finalised The data structures of OS Terrain products and the details of the GML encoding have been based on the draft INSPIRE specification The intention is to align OS Terrain with the final INSPIRE specification when this is available For more information about INSPIRE and UK Location please view the web pages http data gov uk location Computer hardware This product may be used on a wide range of hardware platforms provided sufficient memory and storage
23. e OS Terrain GML is expressed using an EPSG code embedded in a uniform resource name URN urn ogc def crs EPSG 27700 This is a more generic way of expressing the reference system rather than osgb BNG British National Grid used in previous Ordnance Survey products Unique identifiers GML 3 2 requires features and their geometries to have unique identifiers For OS Terrain products the feature identifiers have been structured as follows os t5 tile name gt lt sequential number where the second part abbreviates the product name Geometry identifiers in the GML use the same form but with a geom suffix Therefore for a given release of the product every feature and geometry is guaranteed to have a unique identifier The products will be updated by whole tile refresh and there are no plans to supply feature based change only update When a tile is updated the sequential identifiers are regenerated OS Terrain 5 technical specification chapter 3 v1 1 07 2013 Crown copyright Page 23 of 32 GML grid for OS Terrain 5 Ordnance Survey is committed to open data formats The grid data is supplied as ASCII with GML to enable their use in either format The GML file does not contain any spatial height data as this data has been provided as an external data block that is the ASCII grid file The gml file effectively provides metadata such as location grid spacing and the vertical reference system It also contains spatial
24. ed by application software OS Terrain 5 is available to download as e 5 metre grid in ASCII grid and GML 3 2 1 simple features profile level 0 e 5 metre contours and spot heights in GML 3 2 1 simple features profile level 0 e 5 metre contours and spot heights in Esri shapefile 0 0 e MENNENENENENMNFAANAAZNNKIEEEEEEMMH MEEEEEEEMMEMkK amp ECNNNNNN EN OS Terrain 5 technical specification chapter 1 v1 1 07 2013 Crown copyright Page 21 of 32 Chapter 2 ASCII grid for OS Terrain 5 grid ASCII grid overview ASCII grid is a generic text based DTM format that was originally developed by Esri and it is sometimes referred to as Arcinfo ASCII grid or ArcGrid ASCII This data can be read by most standard GIS software without additional translation The term data structure refers to the organisation and sequence of the records in the data file and not to the geographic topology of the data Data structure Header section The data is specified as a raster grid with the height values being calculated as a mean of the heights across the whole 5 metre pixel To represent this in ASCII grid format the z values are presented 2 5 m from the north west corner of the tile to provide the pixel centre The data is presented in rows reading from west to east creating a row of 1000 values The next row will begin 2 5 m from the western edge 7 5 m south of the northern tile edge under the first value and again
25. el 0 Ordering data OS Terrain 5 can be ordered from the Ordnance Survey online ordering service at https www ordnancesurvey co uk oswebsite business orders index html The data is provided as a full set of Great Britain in tiles and is available as download only The national dataset is supplied as 10 km by 10 km tiles of data There are 10 579 data tiles in the product representing each 5 km by 5 km tile grid square Please note that there are slightly fewer data tiles in the contour set 10 572 due to the lack of real world changes in height in those areas There are metadata files for these tiles It is recommended that a download manager is used to extract the data as this additional functionality will be able to automate the process and organise the data folders as desired There are many commercial and open source download clients available to help manage the data This data is designed to be kept up to date by quarterly full tile resupply in June September December and March each year Coverage and file sizes OS Terrain 5 is full national coverage of Great Britain derived from source data that consists of new content in filled with approximately 1696 Land Form PROFILE data The extent of coverage is in sympathy with our large scale products as the content is derived from source data captured as part of our large scale revision programme OS Terrain 5 will become full coverage of new and also refreshed data content in subsequent up
26. ertyValue which has been implemented in the new OS Terrain contour GML In the shapefile format the GML feature types and attributes have been followed but with the 10 character limit on shapefile fields propertyValue is abbreviated to PROP_VALUE The contours are named master and ordinary which are equivalent to index and standard contours in Ordnance Survey s product Land Form PROFILE Mean high and low water representation in contours In the contour products the mean high and mean low water lines have been derived from our large scale mapping and assigned constant height values based on the average for each tile This average value has been determined from local tide tables Inevitably this means that there is a small discrete step between adjacent tiles There are no contours supplied between the mean high and low water lines The LandWaterBoundary feature type has an attribute of waterLevelCategory which has four possible sub values meanHighWater and meanLowWater or for Scotland meanHighWaterSprings and meanLowWaterSprings This attribution allows their display parameters to be changed to show individual features as desired Spot heights These have been created using an algorithm that selects the highest source data point masspoint within every enclosed contour that has a difference in height of at least 1 metre As they are from an interpolated sur
27. face of the real world they cannot be guaranteed as summits or highest points of the feature but it is intended that in time the height source data will be enriched by additional spot height data The GML data model lists the spot height sub value spotHeightType which allows the potential for formSpot generic mountainPass or summit to be used in future releases of the product Currently all spot height features are attributed as generic It is possible that there will be some instances of spot heights recording lower height values than the enclosing contour but it is likely that these are the result of genuine depressions a M CERE EE CECI OS Terrain 5 user guide chapter 2 v1 1 07 2013 Crown copyright Page 9 of 32 Chapter3 Data metadata and additional files The product will be supplied separately for grid or contour as compressed folders for each geographic tile of data Each compressed folder will consist of data plus a number of additional files This chapter describes these files and their purpose Grid data ASCII and GML lt tile name gt asc Esri ASCII grid data tile name gt gml OGC file for the ASCII grid to enable the data to be loaded as GML format tile name prj File containing the spatial reference system in a format defined by Esri tile name asc aux xml A file that provides parameters to enable default styling in Esri applications This ensures that the shading is consistent across
28. groups of entities and their attributes and the relationship between these entities A data model is independent of a computer system and its associated data structures data point A coordinate pair that defines the position of a point feature or one of a series of coordinate pairs that defines a line feature data quality Attributes of a dataset that define its suitability for a particular purpose for example completeness positional accuracy currency logical structure and so on data structure The defined logical arrangement of data as used by a system for data management a representation of a data model in computer form data type This defines the structure of a data item This in turn determines the range of values it can take and the range of operations that can be applied to it Integer real and character string are examples of data type Some modern programming languages allow user defined types database An organised integrated collection of data stored so as to be capable of use by relevant applications with the data being accessed by different logical paths Theoretically it is application independent but in reality it is rarely so dataset An identifiable collection of related data digital Data that is expressed as numbers digits in computer readable form is said to be digital digital terrain model DTM Also referred to as a digital elevation model DEM this primarily defines the ground surface This will
29. he coast of Britain The mean high and low water lines have been have been derived from our large scale mapping and assigned constant height values based on the average for each tile This average value has been determined from local tide tables The mean high and low water lines were used as heighted breaklines when creating the grid to ensure the grid product is consistent with the contour product This means that there may be a small discrete step in the height of tidal water between adjacent tiles For areas of permanent tidal water the height of the mean low water has been extended out to the tile edge to ensure that the tile is complete Heights in the foreshore area are interpolated between the mean high and low water heights Contours Introduction The contours are presented as polyline and spot height features The contour lines have been divided into tiles for product supply The contour values can be viewed and analysed in a GIS HNENENENENNNENNEEEENEEEMENEMMNMNMNMNMNMMNNANNAMEEEEEEEEEERENNN OS Terrain 5 user guide chapter 2 v1 1 07 2013 Crown copyright Page 8 of 32 The image above shows OS Terrain 5 master and ordinary contours tidal boundaries and labelled spot heights Feature types The terms used for the feature types are drawn from the INSPIRE elevation specification The draft INSPIRE elevation specification requires height values to be held in an attribute called prop
30. he 99 confidence level OS Terrain 5 user guide chapter 4 v1 1 07 2013 Crown copyright Page 16 of 32 Chapter5 The National Grid OS Terrain 5 is supplied as a whole set of Great Britain divided into 5 km by 5 km tiles These tiles are identified by quoting the National Grid reference of the south west corner of the area they cover Ordnance Survey divides Great Britain into squares 100 km by 100 km Each of these squares has a unique two letter reference for example TG in the diagram below To describe a 10 km by 10 km tile first add a two digit reference to the 100 km by 100 km square reference with the easting first followed by the northing for example TG23 Then identify which quadrant of that grid square is required and add SW SE NW or NE to the reference for example TG23SW For additional information on how to use the National Grid visit the Ordnance Survey website at http www ordnancesurvey co uk 10 km by 10 km square TG23 NW NE SW SE TG23SW Re OS Terrain 5 user guide chapter 5 v1 1 07 2013 Crown copyright Page 17 of 32 Annexe A Product and service performance report form Ordnance Survey welcomes feedback from its customers about OS Terrain 5 If you would like to share your thoughts with us please print a copy of this form and when completed post or fax it to the address below bfelddarin REC TR TIE UU Organisation ace iss rire idee ede nu d ev be de nu v dw bee d cu d Address
31. his guide at any time without notice We do not accept responsibility for the content of any third party websites referenced or accessed in or through this guide any contractual documentation and or the Ordnance Survey website HEN OS Terrain 5 user guide preface v1 1 07 2013 Crown copyright Page 3 of 32 Copyright in this guide This guide including for the avoidance of doubt any mapping images reproduced herein is Crown copyright 2013 All rights reserved Any part of this guide may be copied for use internally in your organisation or business so that you can use the product for the purpose for which it is licensed to your organisation or business but not otherwise No part of this guide may be reproduced or transmitted in any form or by any means including electronically for commercial exploitation without the prior written consent of Ordnance Survey No part of this guide may be copied or incorporated in products services or publications that you generate for onward sale or as free promotional or support materials without the prior written consent of Ordnance Survey Data copyright and other intellectual property rights The Crown or where applicable Ordnance Survey s suppliers owns the intellectual property rights in Ordnance Survey digital map data Additional data has been sourced from third parties including public sector information licensed under the Open G
32. ications software Geography Markup Language GML GML was developed by the Open Geospatial Consortium OGC a global organisation of developers and users that aims to maximise the benefit of geographic information GML is a spatially enabled dialect of XML schema Global Positioning System GPS The Navstar global positioning system GPS is a constellation of orbiting satellites that provides navigation data to military and civilian users all over the world The system is operated and controlled by members of the 50th Space Wing located at Schriever Air Force Base AFB Colorado grid The planimetric frame of reference for example the National Grid or the consistent alignment of data points kilobyte Kb A total of 1 024 bytes a measure of data storage capacity line A series of connected coordinated points forming a simple feature with homogeneous attribution mean high Water springs MHW or MHWS Depiction of the encroachment of land by tidal waters at mean highest levels spring tides in Scotland mean low Water springs MLW or MLWS Depiction of limits of tidal waters at mean lowest ebb spring tides in Scotland megabyte Mb A total of 1 048 576 bytes a measure of data storage capacity National Grid The metric grid on a Transverse Mercator projection used by Ordnance Survey on all post war mapping to provide an unambiguous spatial reference in Great Britain for any place or entity whatever the map scale n
33. isualisation and analysis over large areas This is available through OS OpenData OS Terrain 5 OS Terrain 5 is published as both grid and contours each in a variety of formats Both data types are created from the same source data and are supplied as 5 km by 5 km tiles e OS Terrain 5 grid a grid of heighted points with regular 5 metre post spacing e OS Terrain 5 contours a contour dataset of 5 metre interval standard contour polylines which includes index contours at 25 m intervals mean high and low water boundaries and spot heights Applications OS Terrain 5 provides an ideal base to enable the third dimension for other data within an appropriate geographical information system GIS The height data has been created from a source that is also used to update our large scale data products and it can be used in conjunction with many other Ordnance Survey digital products for analytical modelling planning and visual purposes to enable e asset site management e environmental analysis e line of sight planning and view shed modelling e landscape visualisation and fly through sequences e planning and development e signal propagation e wind farm location e flood risk assessment and e a foundation for 3D modelling o OS Terrain 5 user guide chapter 1 v1 1 07 2013 Crown copyright Page 5 of 32 Features e Maintained within our integrated 3 5 year flying programme and synchronised with our other product up
34. ocated on the Ordnance Survey website http www ordnancesurvey co uk xml stylesheet OS TerrainMetadataViewingStylesheet xsl Metadata xml file example This is a section of the xml file in its native format with the location of the style sheet highlighted It can be read like this when opened in an xml viewer or basic file reader lt xml version 1 0 encoding UTF 8 xml stylesheet type text xsl href http www ordnancesurvey co uk xml stylesheet OSTerrainMetadataViewingStylesheet xsl1 gmd MD Metadata xmlns gmd http www isotc211 org 2005 gmd xmlns gml 2 http www opengis net gml 3 2 xmlns xsi http www w3 0rg 2001 XMLSchema instance xmlns gmx http www isotc211 0rg 2005 gmx xmlns gco http www isotc211 0rg 2005 gco xmlns xlink http www w3 org 1999 xlink xsi schemaLocation http www isotc211 org 2005 gmx http eden ign fr xsd isotc211 isofull 20090316 gmx gmx xsd Unique identifier required if this record is being used in a metadata management system lt gmd fileIdentifier gt lt gco CharacterString gt OSTerrain5 NT23NE lt gco CharacterString gt lt gmd fileIdentifier gt lt gmd contact gco nilReason missing gt lt gmd contact gt lt gmd dateStamp gt gco DateTime 2013 01 08T03 22 25 gco DateTime gmd dateStamp Projected Coordinate Reference System gmd referenceSystemInfo lt gmd MD_ReferenceSystem gt gmd referenceSystemIdentifier gmd RS Identifier
35. ofS guar OS Terrain 5 Userguide and technical specification OS Terrain 5 User guide Contents Section Preface Chapter 1 Chapter 2 Chapter 3 Chapter 4 Chapter 5 Annexe A Page no 3 Gontact detalls EET 3 Use of the PprodUCt 3 Purpose and disclaltTier entender he i ee dE eI pha Ea aa acces dae dd a AER aba Aaaa 3 Copyright Irithis guide citt et peteret e e tnn ee pa d n Ra re Mem Ra dod ea d s 4 Data copyright and other intellectual property rights ss m 4 Trademarks TRIESTE DTE 4 Back up provision of the product sess 4 Using gioi go Uo 4 cpi 5 Using is go Uo 5 euge e DM 5 NITIDE aa teede 5 ADPIICALIONS e 5 BUDE 6 herir 6 SUPPLY Etenim E 6 Ordering data 3 iem tec Rd idv eade e dac verdad Pav dads 6 Coverage and file SIZ6S pte E pe Fo e b E E aL ER pti e b buta dus 6 I sisilisseenei uesmu m
36. opes and embankments along the length of the route are also modelled In all other cases the surface must be smooth flat not necessarily horizontal and free from undulations Man made landforms associated with mineral workings and landfill The outer limits of sites for mineral extraction or landfill will be captured Within active sites areas of excavations depositions or temporary access routes that are likely to remain the same until the next cycle of revision are captured Where change is likely to occur within the active portion of the site no data is collected Wholly inactive sites are captured to meet positional accuracy requirements Contained water bodies greater than 0 7 ha In order to respond to the Flood and Water Management Act 2010 the extent of all flat water bodies that are greater than 0 7 hectares in area that is greater than 7 000 cubic metres capacity will have their limits captured to ensure that the presence of the water body can be inferred from the data The height of the water recorded is that at the lowest height of the surrounding data The surface of the water will be flat Conformance The following measurables are used to determine the accuracy and coverage of modelling in the source TIN data Positional accuracy Any height value extracted from any point within the coverage and above the high water mark will meet the positional accuracy requirements Geometric fidelity The DTM will be free of s
37. orthings See rectangular coordinates Open Geospatial Consortium OGC A global organisation of developers and users that aims to maximise the benefit of geographic information origin The zero point in a system of rectangular Cartesian coordinates photogrammetry The science art and technology of obtaining reliable measurements and maps from aerial photographs point A zero dimensional spatial abstraction of an object represented as a coordinate pair point feature A zero dimensional spatial abstraction of an object with its position defined by a coordinate pair Points may also be represented by symbols which may have attributes such as orientation and size OS Terrain 5 technical specification annexe A v1 1 07 2013 Crown copyright Page 31 of 32 positional accuracy The degree to which the coordinates define a point s true position in the world directly related to the spheroid and or projection on which the coordinates system is based rectangular coordinates Also known as x y coordinates and as eastings and northings These are two dimensional coordinates that measure the position of any point relative to an arbitrary origin on a plane surface for example a map projection a digitising table or a VDU screen Route mean square error RMSE This is the square root of the mean of the squares of the errors between observations such as GPS points shapefile This is a data format developed by Esri to describe features su
38. overnment Licence v1 0 Full details of the terms and conditions under which Ordnance Survey digital map data may be processed and or manipulated or copied by a customer whether or not for use on PCs or workstations or for making hard copies are available from the Customer Service Centre please see contact details You should check the terms and conditions with us before using the data It is also the responsibility of the holder of the digital map data to ensure that any plotted or printed output contains the required copyright and database acknowledgements in a conspicuous position Trademarks Ordnance Survey the OS Symbol OS Terrain and Land Form PROFILE are registered trademarks and OS OpenData is a trademark of Ordnance Survey the national mapping agency of Great Britain Adobe and Reader are registered trademarks of Adobe Systems Incorporated Esri and Arclnfo are registered trademarks of Environmental Systems Research Institute Inc OpenGIS and OGC are registered trademarks of Open Geospatial Consortium W3C is a registered trademark of Massachusetts Institute of Technology Back up provision of the product You are advised to copy the supplied data to a back up medium Using this guide The documentation is supplied in portable document format PDF only Free Adobe Reader software which displays the guide incorporates search and zoom facilities and allows you to navigate within Hyperlinks are used to navigate between
39. pikes and reflect the general texture of the terrain Terrain smoothness e Measurable e The absence of spikes or wells in the data that cause a false height value on a data point or interpolated surface e A surface smooth in the real world will appear smooth in the data e Major communication routes will be smooth longitudinally with no steps in the data e Conformity e There must be no spikes or wells in the data larger than the value required to meet the positional accuracy requirements of the geographic area e The difference between gradients in the TIN model at 5 metre intervals should be less than 0 4 40 for major communication routes Feature modelling e Measureable e Data added to model specific features will reflect the correct relationship to itself and immediately surrounding data e Conformity e All features with parallel limits that require modelling will have parallel data points recorded in the data e The relative heights of features in close proximity will be in sympathy ee e OS Terrain 5 user guide chapter 4 v1 1 07 2013 Crown copyright Page 15 of 32 Absolute accuracy Measureable The coordinate position of any point on the surface as represented by the TIN data compared to the true elevation of the same point Conformity The RMSE of a selection of points from the real world compared to the data will be within the values stated No single point will exceed t
40. pplicable to the OS Terrain 5 hereafter referred to as the product which is referred to in the Framework Direct Licence Specific Use Framework Partner Licence or your other customer contract for the product Copyright in this specification This specification including for the avoidance of doubt any mapping images reproduced herein is Crown copyright 2013 All rights reserved Any part of this specification may be copied for use internally in your organisation or business so that you can use OS Terrain 5 for the purpose for which it is licensed to your organisation or business but not otherwise No part of this specification may be reproduced or transmitted in any form or by any means including electronically for commercial exploitation without the prior written consent of Ordnance Survey No part of this specification may be copied or incorporated in products services or publications that you generate for onward sale or as free promotional or support materials without the prior written consent of Ordnance Survey OS Terrain 5 technical specification introduction v1 1 07 2013 Crown copyright Page 20 of 32 Chapter1 Technical specification introduction The purpose of the technical specification is to e provide a brief description of the presentation of OS Terrain 5 in its supply formats and e provide licensed system suppliers with as much detail as necessary to enable OS Terrain 5 files to be easily understood and process
41. r Profile content the Date Flown will be recorded as lt null gt Processing date The date the tile was created by gmd MD DataIdentification gmd citation gmd CI C Ordnance Survey not the date of itation gmd date gmd CI Date gmd date gco Date the real world change or survey gml beginPosition gml endPosition Version number An incrementing number to gmd MD DataIdentification gmd citation gmd CI indicate the number of times the Citation gmd edition gco CharacterString tile has been published Reason for This provides information about gmd MD Dataldentification gmd citation gmd CI change the update of the data and M oed re Ui D ME end rdarelype whether it is creation new or a revision modified verified which is described in the metadata by using lineage below Lineage Text to describe the current status gmd DO_DataQuality gmd lineage gmd LI_Lineage of the tile either created from gmd statement gco CharacterString new imagery some parts revised from new imagery new imagery examined and no change Metadata viewing style sheet To make the xml easier to read an XSLT viewing style sheet is provided OSTerrainMetadataViewingStylesheet xsl which converts the XML to HTML for ease of viewing in a web browser Some browsers and other software will read this automatically if the user is connected to the Internet as its address is referenced in the metadata but it can also be l
42. rain 5 user guide contents v1 1 07 2013 Crown copyright Page 2 of 32 Preface This user guide hereafter referred to as the guide is designed to provide an overview of OS Terrain 5 hereafter referred to as the product and it gives guidelines and advice on how a customer might derive the maximum benefit from the product It assumes a general knowledge of geographic information If you find an error or omission in this guide or otherwise wish to make a comment or suggestion as to how we can improve the guide please contact us at the address shown below under contact details or complete the product and service performance report form at annexe A and return it to us Contact details Our Customer Service Centre will be pleased to deal with your enquiries Customer Service Centre Ordnance Survey Adanac Drive SOUTHAMPTON SO16 OAS General enquiries calls charged at local rate 44 0 8456 05 05 05 Dedicated Welsh Language HelpLine 08456 05 05 04 Textphone deaf and hard of hearing users only please 44 0 23 8005 6146 customerservices ordnancesurvey co uk www ordnancesurvey co uk If you have difficulty reading this information in its current format and would like to find out how to access it in a different format Braille large print computer disk or in another language please contact us on 44 0 8456 05 05 05 Use of the product The terms and conditions upon which the product including this guide is made available to
43. reference information in a software independent form Currently common software packages do not support it in this form but the ASCII grid data can be used alone GML contours and spot heights for OS Terrain 5 Detailed GML model AbstractFeature afeature Type OS Terrain Data Set metadata nominalScsle Integer elevationReference equidistance Distance 0 1 zAbstractFeature boundedBy GM Envelope 0 1 zAbstractGML description CharacterString 0 1 desciptionReference URI 0 1 name GenericName 0 identifier ScopedName 0 1 member n member 0 featureType SpotHeight geometry GM_Point propertyVslue Distance spotHeightType SpotHeightTypeVslue generic member 0 featureType LandWaterBoundary geomety GM_LineString propertyValue Distance waterLevelCstegory WaterLevelValue featureType ContourLine geomety GM_LineString propertyValue Distance contourLineType ContourTypeValue enumeration ContourTypeValue master ordinary auxiliary enumeration WaterLevelValue meanHighWater meanLowWster meanHighWaterSprings meanLowWaterSprings enumeration SpotHeightTypeValue formSpot generic mountainPass summit Spot heights These have been created by an automated process to select the highest mass point that is at least 1 metre above and within every closed contour If the point is the s
44. ructure departs from the bare earth surface and an air gap exists All supported structures will be removed from the data where they would affect the use of the data in a water flow application with due consideration to the positional accuracy requirements of the area Vegetation Areas of vegetation such as hedgerows individual trees and extensive tree cover are removed to ensure the bare earth surface is correctly recorded Vertical features Locations with a vertical change in height or overhang have the height of the top of the feature recorded at the correct planimetric location according to the positional accuracy requirements The height at the lowest point of the vertical feature is recorded according to positional accuracy requirements of the feature but offset from its real world planimetric position to ensure that there is only one z value present in the same location IE LI HE A sil OS Terrain 5 user guide chapter 4 v1 1 07 2013 Crown copyright Page 14 of 32 Major communication routes Major communication routes are major road and rail networks identified in our core database The limits of a road carriageway or railway track bed are modelled to ensure that the route reflects its real world shape Modelling is required for changes in height to meet the positional accuracy requirements to smooth the surface and to remove extraneous features such as road furniture and bridges Any associated sl
45. t was developed by the World Wide Web Consortium W3C XML schemas express shared vocabularies and allow machines to carry out rules made by people They provide a means for defining the structure content and semantics of XML documents Extensible Stylesheet Language Transformations XSLT This is a language for transforming XML documents into objects that can be presented in a format that is more easily read by the user such as HTML for web pages or plain text OS Terrain 5 technical specification annexe A v1 1 07 2013 Crown copyright Page 32 of 32
46. the other values provide functionality to enrich the attribution if required in a later product release LandWaterBoundary geometry GM_LineString propertyValue Distance waterLevelCategory String meanHighWater meanLowWater meanHighWaterSprings meanLowWaterSprings Notes Mean high and low waters apply to tidal waters in England and Wales and the mean high and low water springs apply to those in Scotland Example of the ContourLine feature types lt os member gt lt os ContourLine gml id os t5 sx98se 175 lt os geometry gt gml LineString srsName urn ogc def crs EPSG 27700 gml id 0s t5 sx98se 175 geom gt lt gml posList gt 295487 08 80000 295481 21 80001 48 295480 55 80001 23 295481 75 80000 gml posList gml LineString os geometry lt os propertyValue uom m gt 15 lt os propertyValue gt lt os contourLineType gt ordinary lt os contourLineType gt lt os ContourLine gt lt os member gt OS Terrain 5 technical specification chapter 3 v1 1 07 2013 Crown copyright Page 25 of 32 Example of the SpotHeight feature types lt os member gt lt os SpotHeight gml id os t5 sx98se 0 lt os geometry gt gml Point srsName urn ogc def crs EPSG 27700 gml id os t5 sx98se 0 geom lt gml pos gt 299161 48 84990 56 gml pos gml Point os geometry os propertyValue uom m gt 31 9 lt os propertyValue gt lt os spotHeightType gt generic lt os spotHeightType gt lt
47. ts bridge revetments and earthworks are considered to be part of the bare earth surface Only permanent terrain features those expected to remain until the next revision period or longer are modelled Underground and overhead features Underground and overhead features are by definition not the ground surface and are thus not included in a DTM Underground features are those that are obscured and require excavation to construct Underground features are not recorded and overhead features are removed from the data Terrain smoothness The DTM will be free of spikes and wells that do not reflect the real world terrain A surface that is smooth that is one that consists of a regular plane which may be angled for example a road carriageway or railway trackbed will also appear smooth in the data Edgematching In order to maintain a seamless database of Great Britain the data will present seamless tile edges that are not discernible through inspection of the data values There may be a small edge present or a difference in feature modelling between new content and Land Form PROFILE tiles until the latter has been fully replaced by new data There will also be small edges in tidal areas due to local tidal differences Supported structures Supported structures include bridges viaducts jetties or piers on legs cranes elevated buildings and so on Supported structures are removed from any automatically generated data where the st
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