Temporal terrain shading

Abstract

This paper describes a suite of programs that simulates the lighting effects of the sun or moon on the earth's surface. A digital terrain model (DTM) is typically a two-dimensional regular tessellation of some measured phenomenon, the most common being elevation; such DTMs are known as digital elevation models (DEMs). The tessellation represents an area fixed to the surface of some celestial body, normally the earth. The suite of programs described here simulates the lighting effects of the sun or the moon by taking as input a DEM, a date and a time. The suite determines the position of the sun or the moon relative to the DEM and produces as output a DTM shaded accordingly. The treatment of shadows is also discussed. The resulting DTM may be used to paint a perspective view of the original DEM to provide a more realistic representation of the area.