Exact Radiosity Reconstruction and Shadow Computation Using Vertex Tracing

Michael M. Stark and Richard F. Riesenfeld

Abstract

Methods for exact computation of irradiance and form factors associated with polygonal objects have ultimately relied on a formula for a differential area to polygon form factor attributed to Lambert. This paper presents an alternative, an analytical expression based on vertex behavior rather than the edges the polygon. Using this formulation, irradiance values in a scene consisting of partially occluded uniformly emitting polygons can be computed exactly by examining only the set of apparent vertices visible from the point of evaluation without explicit reconstruction of polygon contours. This leads to a fast, low-overhead algorithm for exact illumination computation that involves no explicit polygon clipping and is applicable to direct lighting and to radiosity gathering across surfaces or at isolated points.

The paper is available in PDF (lossy image compression, 438K). PDF (lossless image compression, 2122K).

The paper (without the color plate) is available in PostScript (288K) and PDF (137K). The color images are available in compressed PostScript (655K) and PDF (658K).

Images from the Paper

512 by 512 single-sample ray-traced images rendered using the algorithm. (a) Evenly arranged occluding objects (32s) producing interference patterns. (b) A particularly difficult scene (shadow image only) of 1000 thin triangles under a large crescent-shaped source (280s). Notice the shape of the source creeping in. (c) a multi-polygon source (98 seconds) and a more pronounced ``pinhole'' effect. (d) Direct lighting of a self-shadowing object (21s). (e) A coarse one-bounce approximation (321 patches, 1s), and (f) the indirect lighting reconstruction (48m). Image (f) was rendered ignoring conjunctive vertices, yet there are only a few erroneous pixels.

Other Images

Mike Stark (mstark@cs.utah.edu)