Pyramid Clipping for Efficient Ray TraversalMaurice van der Zwaan, Erik Reinhard, Frederik W. Jansen, Pyramid Clipping for Efficient Ray Traversal. Rendering Techniques '95. ISBN 3-211-82733-1, pp. 1–10. June 1995. PDF, 77 Kbytes.
Rays having the same origin and similar directions frequently appear in the form of viewing rays and shadow rays to area light sources in ray tracing, and in hemisphere shooting or gathering in radiosity algorithms. The coherence between these rays can be exploited by enclosing a bundle of these rays with a pyramid and by classifying objects with respect to this pyramid prior to tracing the rays. We present an implementation of this algorithm for a bintree spatial sub-division structure and compare the performance with a recursive bintree traversal and the standard grid traversal algorithm. In parallel implementations the tech-nique can be used to create coherent intersection tasks, allowing demand-driven scheduling with low communication overheads.