Room surfaces, windows and external obstructions are subdivided into triangular patches for radiosity calculations, and initial daylight illuminances are calculated from daylight coefficients. The paper describes procedures in which both the form factors for computing inter-reflection and the daylight coefficients are determined by recursively subdividing the spherical triangles subtended by triangular patches. This permits analysis of hidden surfaces and gives also a procedure for tracing specular reflections. An appendix to the paper describes a geometrical framework for the computation.
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