A Class for Run Time Computation of Shadows for Polygonal Objects.

Report No. ARL-TN-156
Authors: Mark A. Thomas
Date/Pages: August 2000; 35 pages
Abstract: The development of realistic synthetic environments for dismounted soldier visualization requires attention to environmental cues. Effects such as shadows provide the soldier information about time of day and orientation. Graphical databases that do not have shadows must compute them at run time. Various methods of computing and displaying shadows exist. This report presents a simple method that is based on bounding volumes. The method provides the rapid generation of shadows. These shadows do not provide light attenuation effects, but the environmental cueing provides valuable information for the dismounted soldier in a synthetic environment. This algorithm provides for rapid, single- pass, polygonally based shadowing of arbitrary objects with a minimum of computation and additional polygons. It is easier to use and faster than ray- tracing methods and can be used in systems that do not provide shadowing through multi-pass rendering, such as PC base image generators. Limitations of this method include the inability to directly model the geometry of the shadowing surface, and the method does not modify the lighting of properties of polygons underneath the shadow. However, the shadow polygon can be used as a mask to shade polygons, given the appropriate programming methodology.
Distribution: Approved for public release
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Last Update / Reviewed: August 1, 2000