Summary

Visibility analyses belong to the most popular applications of digital terrain models. They are based on the so-called line-of-sight problem (LOS problem) in which a profile is intersected with the straight connection between viewpoint and observed object in the terrain. Visibility analyses are subject to external effects, i.e. the earth’s curvature and atmospheric refraction. Those have to be taken into account and they possibly have to be corrected. More complex applications of the LOS problem are the viewshed analysis and the watchtower problem. It is also quite demanding to consider moving objects. Errors in the DTM propagate to the output of a visibility analysis. Monte Carlo simulations are a way to deal with these uncertainties. The calculation of topographic shadows, horizon lines and the potential direct solar radiation are also variants of visibility analyses. The same concepts are valid here.