The same origin ray set query for realistic illumination: Algorithm and analysis

Ari Rappoport*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


The same origin ray set (SORS) is a computational primitive which can be used by ray tracing, radiosity and multiple pass illumination simulation algorithms for realistic image synthesis. A SORS consists of a set of rays emanating from the same point in space. The SORS query computes the first object intersected by each ray and the intersection point. In this paper we present an efficient projection algorithm for computing a SORS query for polygonal scenes. The algorithm achieves its efficiency by separating ray‐polygon intersection detection from the computation of the intersection point between the ray and the polygon's plane. The algorithm can be integrated with all current illumination acceleration schemes. We analyse the projection algorithm and compare it to the alternative of computing the SORS query one ray at a time. The analysis' results are expressed in terms of a few intuitive parameters, measuring the success of the acceleration scheme in culling irrelevant objects and the concentration of the ray set. The projection algorithm can be up to five times more efficient, depending on these parameters and the quality of the image. The relative advantage of the projection increases with image quality.

Original languageAmerican English
Pages (from-to)51-60
Number of pages10
JournalComputer Animation and Virtual Worlds
Issue number1
StatePublished - 1993


  • Computational primitive
  • Illumination simulation
  • Projection
  • Radiosity
  • Ray tracing
  • Same origin ray set (SORS)


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