Digital Terrain Model

Basic Concepts

A DTM is a digital representation of the terrain topography. The term was coined by Miller and Laflame of the Massachusetts Institute of Technology (MIT) in 1958. Their original definition was simply a statistical representation of the continuous surface of the ground by a large number of selected points with known X, Y, Z coordinates in an arbitrary coordinate field.

A number of terms related to DTM have been in use. These include digital elevation model (DEM), digital height model (DHM), digital ground model (DGM), and digital terrain elevation model (DTEM). These terms originated from different countries. DEM was widely used in the United States; DHM came from Germany; DGM was used in the United Kingdom; and DTEM was introduced and used by the U.S. Geological Survey (USGS). They have slightly different meanings. A DGM more or less has the meaning of “a digital model of a solid surface.” In contrast to the use of ground, the terms height and elevation emphasize the “measurement from a datum to the top” of an object. They do not necessarily refer to the altitude of the terrain surface, but in practice, this is the aspect that is emphasized in the use of these terms. Among these terms, DEM is nowadays the most widely accepted one for the digital representation of terrain topography, with terrain heights organized in a matrix form. The meaning of terrain is more complex and embracing. It may contain the concept of height (or elevation) but also attempts to include other geographical elements and natural features. Therefore the term DTM tends to have a wider meaning than does DEM and attempts to incorporate specific terrain features, such as rivers, ridge lines, and break lines, into the model.

Beyond DTM is a model called the digital surface model (DSM). It is a digital representation of the actual terrain surface. In other words, in a DSM, not only the terrain topography but also the spatial features (such as buildings, trees, and roads) on the terrain topography are represented.

If one removes all these spatial features from a DSM, one obtains a DTM. Indeed, the relationship between a DTM and a DSM may be compared with that between a contour line map and a topographic map.

Related to DTM, there are four basic issues: (1) how to acquire a set of data for the generation of DTM, (2) how to generate a DTM, (3) how to control the quality of the DTM, and (4) what can be done with DTM.

The process of construction of a DTM surface is called digital terrain modeling.

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