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
1
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
2
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 http://geoengine.nga.mil/geospatial/SW_TOOLS/NIMAMUSE/webinter/rast_roam.html.
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 http://sedris.org/dwn4trpl.htm. 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 (http://www.acusoft.com/products/sidebyside).
3
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.
4
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
http://www.sedris.org/stc/2001/tu/ctdb/sld005.htm
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
http://www.acusoft.com/products/sidebyside/images/photoalbum_photo_view?b_start=3. 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 http://www.metavr.com/sidebyside.html.
Figure 2: CTDB Terrain
5
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 SemiAutomated 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 (http://www.onesaf.org/), Terrex’s
Terra Vista Pro Builder (http://www.terrex.com/www/ProBuilder.htm), which costs about $15,000,
and AcuSoft’s Side-by-Side Viewer (http://www.acusoft.com/products/sidebyside/). 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.
6
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 http://edc.usgs.gov/geodata/.
DG Terrain Viewer (DGTV) is a freeware program to view 3D digital elevation maps mixed with
data acquired with GPS (http://www.dgadv.com/dgtv/). 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 http://www.dgadv.com/dgtv/.
7
Figure 4: GTOPO30 Terrain
Figure 5: GTOPO30 Terrain
8
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 http://geography.usgs.gov/esic/cdrom/vmap.html.
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
(http://hawk.chiinc.com/c3coreterrain.htm). 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 http://www.tenetdefence.com/product/data.htm.
Figure 6: VMAP Terrain
9
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 http://www.tenetdefence.com/product/data.htm#GEOTIFF and
http://ioc.unesco.org/oceanteacher/resourcekit/M3/Formats/Integrated/GeoTIFF/tif.htm.
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
(http://www.tenetdefence.com/product/data.htm). Figure 7 below is a GeoTIFF terrain picture
courtesy of
http://ioc.unesco.org/oceanteacher/resourcekit/M3/Formats/Integrated/GeoTIFF/tif.htm. 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.
Figure 7: GeoTIFF Terrain
10
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:
-V-89039, MIL-V-89033, MIL-V-89032
-U-89035
ical Chart (DNC) MIL-PRF-89020A
-D-89012A
-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
http://libraries.maine.edu/Spatial/gisweb/spatdb/acsm95/ac95059.html
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 http://earthinfo.nima.mil/geospatial/SW_TOOLS/NIMAMUSE/doc/apps/vpfview/vpfview.htm and http://earthinfo.nima.mil/geospatial/SW_TOOLS/NIMAMUSE/. 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
http://www.tenetdefence.com/product/data.htm. 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.
11
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
http://www.tenetdefence.com/product/data.htm. 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
http://www.tenetdefence.com/product/data.htm.
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 http://www.pcigeomatics.com/.
12
Figure 9: CADRG Terrain at 1M
Figure 10: CADRG terrain at 50K
Figure 11: CIB-10 Terrain
13