Nearly all published terrain elevation data is in the form of data grids. Types of Data Grids and Raster Display Functions described basic approaches to rendering surface data grids with Mapping Toolbox™ functions, including viewing surfaces in 3-D axes. The following sections describe some common data formats for terrain data, and how to access and prepare data sets for particular areas of interest.
The Digital Terrain Elevation Data (DTED) Model is a series of gridded elevation models with global coverage at resolutions of 1 kilometer or finer. DTEDs are products of the U. S. National Geospatial Intelligence Agency (NGA), formerly the National Imagery and Mapping Agency (NIMA), and before that, the Defense Mapping Agency (DMA). The data is provided as 1-by-1 degree tiles of elevations on geographic grids with product-dependent grid spacing. In addition to NGA's own DTEDs, terrain data from Shuttle Radar Topography Mission (SRTM), a cooperative project between NASA and NGA, are also available in DTED format, levels 1 and 2 (see below).
The lowest resolution data is the DTED Level 0, with a grid
spacing of 30 arc-seconds, or about 1 kilometer. The DTED files are
binary. The files have filenames with the extension
N is the level of the DTED product. You can
find published specifications for DTED at the NGA web site.
NGA also provides higher resolution terrain data files. DTED Level 1 has a resolution of 3 arc-seconds, or about 100 meters, increasing to 18 arc-seconds near the poles. It was the primary source for the USGS 1:250,000 (1 degree) DEMs. Level 2 DTED files have a minimum resolution of 1 arc-second near the equator, increasing to 6 arc-seconds near the poles. DTED files are available on from several sources on CD-ROM, DVD, and on the Internet.
For information on locating map data for download over the Internet, see the following documentation at the MathWorks Web site: Finding Geospatial Data.
The United States Geological Survey (USGS) has prepared terrain data grids for the U.S. suitable for use at scales between 1:24,000 and 1:250,000 and beyond. Some of this data originated from Defense Mapping Agency DTEDs. Specifications and data quality information are available for these digital elevation models (DEMs) and other U.S. National Mapping Program geodata from the USGS. USGS no longer directly distributes 1:24,000 DEMs and other large-scale geodata. U.S. DEM files in SDTS format are available from private vendors, either for a fee or at no charge, depending on the data sets involved.
The largest scale USGS DEMs are partitioned to match the USGS 1:24,000 scale map series. The grid spacing for these elevations models is 30 meters on a Universal Transverse Mercator grid. Each file covers a 7.5-minute quadrangle. (Note, however, that only a subset of paper quadrangle maps are projected with UTM, and that USGS vector geodata products might not use this coordinate system.) The map and data series is available for much of the conterminous United States, Hawaii, and Puerto Rico.