Geometric Quality in Geographic Information

A typical way to build surface numerical models or Digital Elevation Models (DEMs) for Geographical Information Systems (GIS) is by processing the stereo images obtained from, for example, aerial photography or SPOT satellite data. These GIS can perform many computations involving their geographic databases. The quality control of a geographic database, and in particular the topological and geometric integrity, are, therefore, important topics (Guptill & Morrison, 1995; Harvey, 1997; Laurini & Milleret-Raffort, 1993; Ubeda & Servigne, 1996). The geometric quality control of the stored DEM is what we are concerned with here. “Quality” means the geometric precision measured in terms of the difference between a DEM and a reference DEM (R-DEM). We assume the R-DEM is a faithful model of the actual surface. Its point density may be greater than the DEM point density.