Developed for use in the ModSAF simulation project, the ...



Survey of Digital Terrain Formats

and Software for Implementation into

ACIN’s COMPOSER Project

Laurence Chapman, David Hamel

Dr. David Breen, Dr. Kapil R. Dandekar

September 31st, 2005

APPLIED COMMUNICATIONS AND INFORMATION NETWORKING

(ACIN)

Modeling and Simulation of on-the-move Networks

(in support of COMPOSER)

(ACIN Phase 5)

Deliverable 6.2

Restricted Access: U.S. Citizens Only

Table of Contents

I. Introduction 3

II. DTED 3

III.CTDB 4

IV. OTF. 6

V. GTOPO30 7

VI. VMAP 9

VII. GeoTiff 10

VIII. VPF 11

IX. RPF. 12

I. Introduction

This document was written to support the specification of COMPOSER's GUI (Graphical User Interface) by identifying and surveying the available digital terrain formats needed to support the Net Planner, Net Visualizer , and the CES. In the following sections we survey a number of digital terrain formats along with the available software to work with the respective terrains.

II. DTED

Digital Terrain Elevation Data (DTED) is a uniform matrix of terrain elevation values. The data is produced at three levels of detail, DTED Level 0, DTED Level 1, and DTED Level 2. The data file at all levels is an ASCII file which contains for each 15' by 15' area of a 1° by 1° cell defined by whole degree latitude and longitude lines, the minimum and maximum elevation, the mean elevation, and the standard deviation. DTED files are similar to USGS DEM files, but are originally designed by the National Imagery and Mapping Agency. These file can be downloaded at .

DTED Level 0 post spacing is 30 arc seconds (nominally one kilometer). They are usually given in 1-degree square files that have 121*121 data points. Level 0 contains .avg, .min, and .max files that contain the average, minimum and maximum terrain elevation value associated with each elevation value. Level 0 was derived from Level 1 to support a federal agency requirement and is available freely through the Internet. This reduced resolution is not intended to be used for any precision activity involving the safety of the public.

DTED Level 1 is the basic medium resolution data source for all military activities and systems that require land form, slope, elevation, and/or gross terrain roughness in a digital format. Level 1 is a uniform matrix of terrain elevation values with post spacing every 3 arc seconds (~100 meters). The content is equivalent to the contour information represented on a 1:250,000 scale map.

DTED Level 2 is the basic high resolution data source. It has a post spacing of one arc per second (~ 30 meters). The content is equivalent to the contour information represented on a 1:250,000 scale map.

There are many software packages available for use with DTED files. Sedris is a company that makes terrain tools for the government and public domain. Information about the Sedris Company and their terrain tools can be found at . Sedris stands for “Synthetic Environment Data Representation Interchange Specification”. Sedris allows for terrain format interoperability by using the Sedris Transmittal Format (STF) as a universal format for converting between all other formats. Sedris has a number of software tools that can be used to convert DTED files into other formats. Sedris allows for the interchange between DTED and STF and vice versa, so that anyone can start with a DTED terrain and convert it into many different supported terrain formats, e.g. CTDB, shape converter, etc. Sedris tools are free to anyone that is registered to the site. This facilitates its acceptance by the public domain as a standard interoperability terrain format. Figure 1 below is an example of what a DTED Level 0 terrain looks like. The elevation detains can been seen from the shaded areas. A more detailed look at the terrain elevation can be seen using different terrain viewers such as AcuSoft’s Side-by-Side Viewer ().

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Figure 1: DTED Terrain from the NGA Raster Roam Site

III. CTDB

Compact Terrain Database (CTDB) is a highly compact representation format used by the JointSAF/ModSAF/OneSAF testbed Computer Generated Forces (CGF). CTDB is composed of a terrain skin and bathymetry. Physical features are composed of trees, canopies, laid linears, volume models, roads and river networks. They affect indivisibility, with abstract features composed of aerial feature boundaries and are used for path planning. Elevation data is stored in several ways, using elevation grids, Triangulated Irregular Networks (TIN) and a hybrid of grids and TINs. CTDB supports two coordinate systems. The first is Modified Universal Transversal Mercator (UTM), which sometimes is referred to as the SIMNET coordinate system. The SIMNET coordinate system is a rectangular coordinate system with origin at the SW corner of the database. The second is the Global Coordinate system (GCS). The GCS is based on the tilting of the Earth’s surface into cells. Each cell has a local Cartesian frame of reference. The positions in GCS are specified by four coordinates: X,Y, Z and the cell ID. There is one CTDB per cell.

There are eight different versions of the CTDB format, 1 though 8, with format 8 being the latest version. Format 1 was the original CTDB format. Format 2 added type attribute to microterrain. Microterrain just provides more detail on gridded terrain. Format 3 was the first to integrate abstract features. Format 4 added support for the TINs. Format 5 added the GCS, bathymetry with water surfaces, and generalization of the linear and volume models. Format 6 added Multiple Elevation Surface (MES) structures, aggregate features, and variable diagonalization for terrain grids. Format 7 is the current version used in ModSAF, which the compiler builds this version by default. Format 8 is the most current format which added FACC codes to physical and abstract features but was never implemented for ModSAF.

The CTDB is a more compact terrain format but is also very complex, which is why it is not widely used. The complexity stems from the data organization within the terrain file and all the different types of features it can display. Some features include roads, railroads, rivers, tree canopies, soil defragmentation areas (lakes, marshes, etc), off road segments, complex sturtures like buildings, MES and tactical signs. In order to keep the terrain files compact with such abstract features, a complex data organization scheme was utilized. This organization of data makes it difficult for users to extract simple terrain information from the file and also because of all the abstract features overlaying the terrain information. More information about the CTDB can be found at

Sedris makes conversion tools for this terrain format that allows users to convert from the CTDB format into theiSTF format and from an STF format into the CTDB format. This allows users to convert CTDB into other terrain formats and vice versa. You cannot download data in a CTDB format because it was created by the OneSAF organization for the specific use in their Objective Testbed Baseline (OTB) software package. In order to get a terrain in the CTDB format without having the OTB software, a terrain conversion must be done. Arcsoft has a software package called Side-by-Side Viewer which can display a CTDB and then create a 3D representation of the CTDB. An example of this can be seen is Figure 3 courtesy of . Many commercial vendors integrated the CTDB format because of its ability to display highly complex structures in a compact manner. Figure 2 is a CTDB terrain example that shows no elevation data and is courtesy of .

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Figure 2: CTDB Terrain

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Figure 3: Side-by-Side Viewer of CTDB to 3D Representation

IV. OTF

OTF (Objective Terrain Format) is a terrain database format created by OneSAF (One Semi-Automated Forces). This file format contains four types of files, a database header file (.dhf), an OTF file (.otf), three network database files (.nw), and a single elevation map file (elevation_map).

The Database Header File stores the header file for the database, the Geotiles in the database, and information about the pages in the database. A Geotile contains descriptions and links to all available data for a single region at one level of detail. The header contains version information, the name of the database, the latitude and longitude of the database and whether the database is big or little endian. The OTF file is created in 4 steps. Build the Geotile header, compile the terrain triangles, build the features in the Geotile, and compile the UHRB's (Ultra-High Resolution Buildings). The Network Database is the collection of all three .nw files for each Geotile. Each of the three files contain a set of coordinates, a set of segments, and a header that contains metadata as well as preliminary information intended to speed up the access of information contained in the file. The Elevation Map consists of a header section, followed by a lookup table of geodetic elevations. The elevations are calculated from elevation calls to the OTF database.

Currently, the only software available for the use with OTF terrain formats is the One Objective System (OOS) software package created and used by OneSAF (), Terrex’s Terra Vista Pro Builder (), which costs about $15,000, and AcuSoft’s Side-by-Side Viewer (). Terrex’s Terra Vista software is a comprehensive software package that can be used with many terrain formats, including all of the terrains supported by the OneSAF team. OneSAF has given the specifications for the OTF format to many commercial vendors so that they can create their own commercial software tools to work with the OTF format. AcuSoft’s Side-by-Side Viewer can work with the OTF files. It allows for conversion and simultaneous viewing of the multiple databases. The beta version for this program is free.

V. GTOPO30

GTOPO30 is a global digital elevation model (DEM) covering the full extent of the latitudes from 90 degrees south to 90 degrees north, and the full extent of the longitudes from 180 degrees east to 180 degrees west. The horizontal grid spacing is 30-arc seconds resulting in a DEM having dimensions of 21,600 rows and 43,200 columns. It is based on data derived from eight sources of elevation, Digital Terrain Elevation Data, Digital Chart of the World, USGS Digital Elevation Models, Army Map Service Maps, International Map of the World, Peru Map, New Zealand DEM, and the Antarctic Digital Database, including vector and raster data sets. GTOPO30 uses different sources, hence differences in topographic detail is evident.

The GTOPO30 data is divided into 33 pieces or tiles. The data for each tile contains a set of 8 files, a DEM file (.dem), the digital elevation model data, which is provided as a 16-bit integer in a simple binary raster; a header file (.hdr), an ASCII file containing size and coordinate information for the DEM; a world file (.dmw), an ASCII file containing coordinate information; a statistics file (.stx), an ASCII file that lists band number, minimum value, maximum value, mean value, and standard deviation; a projection file (.prj), an ASCII text file which describes the projection of the DEM and source map image; a shared relief image (.gif), a generalized version of GTOPO30 that provides an overview of the data in each tile; a source map (.src), a 8-bit binary image which has values that indicate the source used to derive the elevation for every cell in the DEM; and a source map header file (.sch), an ASCII file similar to the DEM header file that contains size and coordinate information. These files are available freely through anonymous FTP at the EROS Data Center at .

DG Terrain Viewer (DGTV) is a freeware program to view 3D digital elevation maps mixed with data acquired with GPS (). It can be used just for viewing terrain meshes or for displaying tracks and waypoints projected on the terrain mesh. Since any kind of vector information can be loaded on 3 different GPS formats, DGTV is being used for civil engineering purposes such as hydraulics and terrain slope analysis in cities. The Video sequence feature is also being used by the military to display in 3D the animated tracks of experimental flights, ground attack paths and air-to-air interception. Rocket enthusiasts are plotting near parabolic tracks that go up to 5km altitude. This software does not include any conversion tools or allow for simulation with the supported terrain type. It is only intended for viewing the terrain and track planning. Figure 4 and 5 below shows an example of what a GTOPO30 terrain would look like courtesy of DG Terrain Viewer at .

Figure 4: GTOPO30 Terrain

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Figure 5: GTOPO30 Terrain

VI. VMAP

Vector Map (VMap) was designed to provide vector-based geospatial data at medium and high resolution. It consists of geographic, attribute, and textual data. The primary source for the database is the 1:1,000,000 scale Operational Navigation Chart series co-produced by the military mapping authorities of Australia, Canada, United Kingdom, and the United States. VMap is produced and maintained by the National Imagery and Mapping Agency (NIMA). It was formerly know as Digital Chart of the World. VMap has 3 levels of detail, Level 0 which has a scale of 1:1,000,000, Level 1 which has a scale of 1:250,000, and Level 2 which has a scale of 1:100,000. VMap can be obtained at .

Each VMap database is a vector-based product implemented in Vector Product Format (VPF), which provides a standard format for storing digital vector cartographic data. It is designed to support Geographic Information System (GIS) applications with geographic data at a small resolution. The complete database contains more than 1,800 megabytes of vector data. The data is separated into ten thematic layers, where each layer contains thematically consistent data. The VMap data is stored in decimal degrees as geographic coordinates with southern and western hemispheres having a negative sign for latitude and longitude, respectively. It includes major airports, elevation contours, coastlines, international boundaries and populated places. The World Geographic Reference System (GEOREF) coordinate system is used for the geographic location of tiles.

VMAP files can be used by many different software packages. CHI Systems Inc. C3Core Terrain Server is one of these software packages and is not freeware (). The software supports terrain and mobility calculations, contains elevation tools, and mobility and terrain analysis tools. Sedris also has a conversion tool for the VMAP format that is freely available. Figure 6 below is an example of what a VMAP terrain looks like and is courtesy of .

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Figure 6: VMAP Terrain

VII. GeoTIFF

Aldus-Adobe’s Tagged-Image File Format

TIFF has emerged as one of the world’s most popular raster file formats, but is limited in cartographic applications since no publicly available, stable structure for conveying geographic information presently exits in the public domain. Several private solutions exist for recording cartographic information in TIFF tags but remain in the private domain. There are companies such as Intergraph, ESRI and Island Graphics with their own geographic solutions which are proprietary or limited by specific application to their software’s architecture. Many companies request a public TIFF format be created. TIFF data comes from satellite imaging platforms, aerial platforms, and scans of aerial photography or paper maps. GeoTIFF format is a non-proprietary geographic TIFF format. The purpose of GeoTIFF is to provide information that lets raster imagery (scanned maps, satellite images, results of geographic analysis, etc) be read automatically into correct position and scale within many GIS software systems. GeoTIFF implements a tag structure that embeds the geographic information methodically and interoperably (and invisibly to most users) inside the TIFF file. GeoTIFF does not intend to become a replacement for existing geographic data interchange standards; rather it aims to augment an existing popular raster-data format. More information about the GeoTIFF format can be found at and .

The raster-roam website allows for download of GeoTIFF format for geographic data. Sedris has developed free tools for the conversion of this format into their native Sedris Transmittal Format (STF). They have many conversion tools available for not only GeoTIFF but almost all the terrain formats used in industry. Another software package named MapLink Pro by Tenet can also be used to work with GeoTIFF files and many others (). Figure 7 below is a GeoTIFF terrain picture courtesy of . The GeoTIFF picture does not display different elevations well. It is only a digital terrain of a scanned map. This format will not be suitable for simulation.

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Figure 7: GeoTIFF Terrain

VIII. VPF

Vector Product Format data was used by the US Defense Mapping Association for the distribution of its data sets. This format was also used for the Digital Chart of the World (DCW). VPF is designed to be compatible with a wide variety of applications and products. VPF allows application software to read data directly from computer-readable media without prior conversion to an intermediate form. VPF uses tables and indexes that permit direct access by spatial location and thematic content and is designed to be used with any digital geographic data in vector format that can be represented using nodes, edges, and faces. VPF data is distributed by NIMA.

Supported products include:

• Vector Map Levels 0, 1 and 2 (VMap) MIL-V-89039, MIL-V-89033, MIL-V-89032

• Urban Vector Map (UVmap) MIL-U-89035

• Digital Nautical Chart (DNC) MIL-PRF-89020A

• Foundation Feature Data (FFD)

• Tactical Ocean Data Level2 0, 1, 2 and 4 (TOD)

• Vector Interim Terrain Data (VITD)

• World Vector Shoreline Plus (WVSPlus) MIL-D-89012A

• Digital Topographic Data (DTOP) MIL-PRF-89049/3

The Defense Mapping Agency (DMA) uses the vector Product Format (VPF) military standard because of demanding requirements of military and maritime applications. The VPF standard defines the conceptual and physical data model on which all DMA vector products are based. It uses a geo-relational model which is organized into five hierarchical levels: Database Level, Library Level, Coverage Level, Feature Level, and Primitive Level. Limitations caused by restrictions in computer memory or distribution media capacity require that large geospatial databases be divided into manageable units, or tiles. VPF supports tiling using a concept of organizing primitives by geographic units and provides inter-tile topology to maintain geographic features in a logically continuous manner across tile boundaries. As a Military Standard, VPF documentation is available to the public through the Defense Printing Service Detachment Office. More information on the VPF can be found at

There are a few software packages that use VPF. VPFView is a program in the NIMAMUSE software package that is designed to access any database implemented in VPF. More info on NIMAMUSE can be found at and . NIMAMUSE was developed by the DMA to provide a sample suite of software exploiting DMA digital products. The Tactical Mapping System was developed by TRW, Systems Integration Group, as a mapping component of the US Navy’s Tactical Aircraft Mission Planning System (TAMPS) which is used by Naval tactical aircraft pilots to perform flight, target, and route planning. Sedris also makes a conversion tool to convert from VPF into STF, which then can be converted into a few different formats including CTDB, GeoTIFF and so on. Figure 8 below is one example of a VPF terrain courtesy of . Since there are a few different formats that use VPF as the structure to their terrain, it might be possible to simulate in one of them.

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Figure 8: VPF Terrain

IX. RPF

RPF is Raster Product Format, which is the underlying format of Compressed ARC Digitized Raster Graphics (CADRG) and Controlled Image Base (CIB). CADRG are digital raster representations of paper graphic products which can come in different resolutions. CADRG is derived directly from ADRG and other digital sources through down sampling, filtering, compression and reformatting to the Raster Product Format (RPF) standard. When processed during production, these scanned maps and digital images have been reprojected and organized to contribute to a seamless, world-wide image database. Figure 9 is a CADRG at 1M (Low resolution) and Figure 10 is a CADRG at 50K (High resolution) courtesy of . CIB is a panchromatic imagery format published by NIMA to allow distribution of large areas of tiled imagery. CIB is structured using the NIMA RPF but the CIB standard defines the individual image format and compression ratio. CIB comes in many different resolutions including CIB-5 and CIB 10, which are the standard 5 meter and 10 meter resolution. Figure 11 is a picture of a CIB Terrain courtesy of .

The RPF is a standard data structure for geospatial databases composed of rectangular arrays of pixel values (e.g. in digitized maps or images) in compressed or uncompressed form. RPF is intended to enable application software to use the data in RPF format on computer-readable interchange media directly without further manipulations or transformation. The RPF is intended to define a common format for interchange of raster data between producers of such data in DoD and users of the data, to help facilitate interoperability among mission-critical system.

Sedris does not make any conversion tools for this terrain format. PCI Geomatics software uses Generic Database (GDB) Technology that lets the user directly read and write raster, vector and other information form an extensive list of supported file types. The software contains over 100 different format types and can be found at .

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Figure 9: CADRG Terrain at 1M Figure 10: CADRG terrain at 50K

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Figure 11: CIB-10 Terrain

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