A digital elevation model (DEM) or digital surface model (DSM) is a 3D computer graphics representation of elevation data to represent terrain or overlaying objects, commonly of a planet, moon, or asteroid. A "global DEM" refers to a discrete global grid. DEMs are used often in geographic information systems (GIS), and are the most common basis for digitally produced relief maps.
A digital terrain model (DTM) represents specifically the ground surface while DEM and DSM may represent tree top canopy or building roofs.
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
The elevation of a geographic location is its height above or below a fixed reference point, most commonly a reference geoid, a mathematical model of the Earth's sea level as an equipotential gravitational surface .
The term elevation is mainly used when referring to points on the Earth's surface, while altitude or geopotential height is used for points above the surface, such as an aircraft in flight or a spacecraft in orbit, and depth is used for points below the surface.
Processed LiDAR point cloud showing not only elevation, but heights of features as well.[citation needed][clarification needed]
Sign at 8,000 feet (2,438 m) in the San Bernardino Mountains of southern California (2009)
Landsat Image over SRTM Elevation by NASA, showing the Cape Peninsula and Cape of Good Hope, South Africa in the foreground.[1]