DEM versus DTM versus DSM

The terms DEM (Digital Elevation Model), DTM (Digital Terrain Model) and DSM (Digital Surface Model) are all usually used to refer to various types of continuous, three-dimensional geospatial data.  There is a fair amount of confusion in the literature, however, about which term refers to which types of data.  If you want to get really confused about these terms, there is a great Wikipedia article that goes into confusing detail about this terminology confusion.

In the world of ENVI, we really only use the term DEM.  A DEM in ENVI is understood to be an image (raster) in which the pixel values represent the ground elevation above sea level.  If there are buildings, trees or other features on the ground in the area of a given DEM, those features are assumed to not be included in the elevation values included in the DEM.

In E3De, our new LiDAR visualization and analysis software environment, the documentation includes all three terms.  A DEM in E3De is understood to be an image (raster) or a set of vector contours, in which the values (pixel values or contour levels) represent the ground elevation above sea level.  A DSM in E3De is understood to be an image (raster) in which the pixel values represent the elevations above sea level of the ground and all features on it.  So, if there are buildings or trees in the area, for example, the DSM can include those building and tree heights in the elevation values it provides.  E3De does not create any datasets that it refers to as DTMs, but the documentation for E3De does refer to DTMs in a couple of places.  Where it does, it means a raster DEM.  In other words, to E3De, a DTM is an image (raster) in which the pixel values represent the ground elevation above sea level.