Generating Viewsheds without Using Sightlines

Abstract

A new simple algorithm for computing viewsheds using gridded digital elevation models (DEMs) is presented. By using reference planes rather than sightlines, considerable savings in computing time can be made. The time for computing a viewshed for every point of a DEM is constant, in contrast to with sightline-based algorithms in which the computing time varies with the location of a point in a DEM. The algorithm was tested by use of the DEMs of two areas. The viewshed of every point of both DEMs was calculated. The viewshed is, as might be expected, found to be strongly influenced by both relative and absolute position. Viewpoints at peaks and ridges have more visible area than the viewpoints at pits or bottom of valleys. However, the viewshed of the viewpoints at peaks or ridges with flat local ground surface, especially in plateau-like areas, could be less than the viewpoints in pits or bottom of valleys.