Occlusion Evaluation In Hierarchical Radiosity

In any hierarchical radiosity method, the most expensive part is the evaluation of the visibility. Many methods use sampling and ray casting to determine this term. Space partitioning considerably speeds up the computation process. Partitioning with shafts, leads ro a quite precise subdivision of 3D space, as far as interactions between pair of objects are concerned.The use of bounding boxes allows to speed-up many computations, such as collision or intersection detection. Those intersections can profitably be used to determine visibility between objects. Axis aligned bounding boxes allow very fast evaluation of intersection, but are not that precise, whereas oriented bounding boxes, much closer to the 3D object achieve more accurate visibility evaluation.We present here a method that allow to quickly and accurately determine the relative position of an object and a shaft (inside, outside, occluding), and how to implement it in a hierarchical radiosity algorithm, in order to limit the hierarchy construction where not necessary.