Digital Elevation Models

A DEM is a collection of discrete elevation points at regularly spaced intervals, while a DTM defines topographic shapes by elevation points at significant topographic features which reflect abrupt changes in relief such as incised streams, ridge lines, and slope breaks.

In either case, these data points provide a regular (DEM) or irregular (DTM) pattern of elevation information that can be used for many purposes, such as the generation of a triangular irregular network (TIN), where groupings of three elevation points create adjoining triangular surfaces which mathematically approximate the ground surface.

We utilize two principal methods to collect digital elevation information. The first is a direct measurement process using analytical or softcopy stereoplotter systems. Utilizing analytical stereoplotters, an operator manually defines breaklines and mass points from which the elevation model is generated. If the photographs are scanned, then semi-automated image correlation can be done utilizing softcopy systems.

The second method is an automated measurement process of elevation using LIDAR or interferometric radar systems. Following collection of raw elevation points, the data is post-processed resulting in a digital elevation model of the earth's surface.

The Air Survey Image Library