A unified hierarchical algorithm for global illumination with scattering volumes and object clusters

Abstract

-This paper presents a new radiosity algorithm that allows the simultaneous computation of energy exchanges between surface elements, scattering volume distributions, and groups of surfaces, or object clusters. The new technique is based on a hierarchical formulation of the zonal method, and efficiently integrates volumes and surfaces. In particular no initial linking stage is needed, even for inhomogeneous volumes, thanks to the construction of a global spatial hierarchy. An analogy between object clusters and scattering volumes results in a powerful clustering radiosity algorithm, with no initial linking between surfaces and fast computation of average visibility information through a cluster. We show that the accurate distribution of the energy emitted or received at the cluster level can produce even better results than isotropic clustering at a marginal cost. The resulting algorithm is fast and, more importantly, truly progressive as it allows the quick calculation of approximate solutions with a smooth convergence towards very accurate simulations.

A Clustering Algorithm for Radiance Calculation In General Environments

“…It is interesting to note the benefit of storing the radiant intensity in the form of a directional distribution, since the transfer estimate does not require the interrogation of the cluster contents. This represents a potential gain over previous hierarchical clustering algorithms [6,10].…”

“…Previous work along this line has proposed to compute equivalent isotropic extinction coefficients for object clusters based on the total area they contain [6] …”

“…We assume here that the reader is familiar with hierarchical radiosity and clustering algorithms [3,10,6]. In these methods, a hierarchical subdivision structure of 3D space is used to collect surfaces into clusters.…”

“…is used as in [6] to compute approximate transmission through a cluster, as it represents the rate of attenuation per unit length in the direction of interest. Note that the factor of p from the isotropic formula is no longer present, since it accounted for the averaging over all directions.…”

“…Our preliminary implementation uses an estimate of the energy transferred between two objects u and s (objects can be surfaces or clusters [6]). To obtain this estimate we select two sample points in .…”