 There is no universal usage of the terms "digital elevation model" (DEM), "digital terrain model" (DTM) and "digital surface model" (DSM) in scientific literature.In most cases the term "digital surface model" represents the earth's surface and includes all objects on it.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).