Computing the amount two objects see each other can be approximated with ray tracing. By forming a tight polyhedral volume around the two objects and quickly comparing it to a bounding volume hierarchy, we generate a reusable candidate set of objects and bounding volumes to test with a set of rays. A postscript version of this paper is available online. Discusses practical meshing, energy balance, sampling, and display problems when using meshed radiosity. Discusses using monte carlo techniques and ray tracing to create atmospheric volume effects.
Technique used in The Key is Light film to create the dusty shafts of light in the church.
Essentially quickly clipping a ray against the set of planes defining the polyhedron. Code available online in the Graphics Gems Repository . Occlusion testing for meshed radiosity can be done with ray tracing. Further discussion on the topic is available in The Ray Tracing News, v. 2, no. 6 . Various efficiency scheme, spline surface intersection, and ambient lighting tricks.