A Digital Elevation Model (DEM) is a collection of discrete elevation points at regularly spaced intervals. The model reflects abrupt changes in relief such as incised streams, ridge lines, and slope breaks.
The Two Methods to Obtaining a DEM
1. Direct extraction of topographic information using well established photogrammetric techniques. This method has evolved from manual interactive collection of breaklines and mass points to a fully automated method, using image matching techniques.
2. Using laser and radar-based sensors to automatically derive elevation information.
Regardless of the method used, the recorded data is post-processed to generate the final DEM.