Digital elevation model

In contrast to a DSM, the digital terrain model (DTM) represents the bare ground surface without any objects like plants and buildings (see the figure on the right).

DTMs are created from high resolution DSM datasets using complex algorithms to filter out buildings and other objects, a process known as "bare-earth extraction".

The digital elevation model itself consists of a matrix of numbers, but the data from a DEM is often rendered in visual form to make it understandable to humans.

Mappers may prepare digital elevation models in a number of ways, but they frequently use remote sensing rather than direct survey data.

Older methods of generating DEMs often involve interpolating digital contour maps that may have been produced by direct survey of the land surface.

Note that contour line data or any other sampled elevation datasets (by GPS or ground survey) are not DEMs, but may be considered digital terrain models.

One powerful technique for generating digital elevation models is interferometric synthetic aperture radar where two passes of a radar satellite (such as RADARSAT-1 or TerraSAR-X or Cosmo SkyMed), or a single pass if the satellite is equipped with two antennas (like the SRTM instrumentation), collect sufficient data to generate a digital elevation map tens of kilometers on a side with a resolution of around ten meters.

[19] The SPOT 1 satellite (1986) provided the first usable elevation data for a sizeable portion of the planet's landmass, using two-pass stereoscopic correlation.

[24] New Horizons' Long Range Reconnaissance Imager used stereo photogrammetry to produce partial surface elevation maps of Pluto and 486958 Arrokoth.

An alternative free global DEM is called GTOPO30 (30 arcsecond resolution, c. 1 km along the equator) is available, but its quality is variable and in some areas it is very poor.

A much higher quality DEM from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) instrument of the Terra satellite is also freely available for 99% of the globe, and represents elevation at 30 meter resolution.

The SRTM30Plus dataset (used in NASA World Wind) attempts to combine GTOPO30, SRTM and bathymetric data to produce a truly global elevation model.

A novel global DEM of postings lower than 12 m and a height accuracy of less than 2 m is expected from the TanDEM-X satellite mission which started in July 2010.

[38] Many national mapping agencies produce their own DEMs, often of a higher resolution and quality, but frequently these have to be purchased, and the cost is usually prohibitive to all except public authorities and large corporations.

3D rendering of a DTM of Tithonium Chasma on Mars
Surfaces represented by a Digital Surface Model include buildings and other objects. Digital Terrain Models represent the bare ground.
Heightmap of Earth's surface (including water and ice), rendered as an equirectangular projection with elevations indicated as normalized 8-bit grayscale, where lighter values indicate higher elevation
Relief map of Spain's Sierra Nevada, showing use of both shading and false color as visualization tools to indicate elevation
MOLA digital elevation model showing the two hemispheres of Mars. This image appeared on the cover of Science magazine in May 1999.
Gatewing X100 unmanned aerial vehicle
Digital Elevation Model - Red Rocks Amphitheater, Colorado obtained using a UAV
Bezmiechowa airfield 3D Digital Surface Model obtained using Pteryx UAV flying 200 m above hilltop
Digital Surface Model of motorway interchange construction site . Note that tunnels are closed.
Example DEM flown with the Gatewing X100 in Assenede
Digital Terrain Model Generator + Textures(Maps) + Vectors
STL 3D model of the Moon with 10× elevation exaggeration rendered with data from the Lunar Orbiter Laser Altimeter of the Lunar Reconnaissance Orbiter