Optimising Visibility Analyses Using Topographic Features on the Terrain

The advantages of using the fundamental topographic features of a surface namely the peaks, pits, passes, ridges and channels as the observers (viewpoints) in visibility computation is presented. Considerable time can be saved without any significant information loss by using the fundamental topographic features as observers in the terrain. This optimisation is achieved because of a reduced number of observer-target pair comparisons thus establishing the Reduced Observers Strategy. The method has been demonstrated for a gridded digital elevation model. Due to this selected sampling of observers in the terrain, there is an under-estimation of the viewshed of each point. Two simple methods for assessing this uncertainty have been proposed.