Isotropic Clustering for Hierarchical Radiosity - Implementation and Experiences



Although Hierarchical Radiosity was a big step forward for finite element com-
putations in the context of global illumination, the algorithm can hardly cope with
scenes of more than medium complexity. The reason is that Hierarchical Radiosity
requires an initial linking step, comparing all pairs of initial objects in the scene.
These initial objects are then hierarchically subdivided in order to accurately rep-
resent the light transport between them. Isotropic Clustering, as introduced by
Sillion, in addition creates a hierarchy above the input objects. Thus, it allows for
the interaction of complete clusters of objects and avoids the costly initial linking
In this paper, we describe our implementation of the isotropic clustering algo-
rithm and discuss some of the problems that we encountered. The complexity of
the algorithm is examined and clustering strategies are compared.