# Efficient Radiosity for Daylight Simulation in Closed Environments

Radiosity is a useful tool for architects and lighting engineers to
simulate illumination in the interior of buildings. Unfortunately, the
computation time for radiosity is very high. However, radiosity
algorithms can take advantage of special scene properties of specific
classes of environments. Exploiting the additional information about
the scene structure of a particular class can decrease the computation
time significantly. The aim of this paper is to speed up the radiosity
computation for the class of closed environments without artificial
light sources.
The first restriction on the scene is that it is closed. The reason for
this restriction is the fact that radiosity is based upon the energy
conservation principle, that means that at any time the amount of
emitted energy equals the amount of absorbed energy plus the amount of
energy leaving the scene. In closed scenes no energy leaves the scene,
thus simplifying the radiosity computation. However, this restriction
does not impose problems, because radiosity is mostly used for interior
scenes. The second restriction is that only daylight can be considered.
Radiosity algorithms solve a set of equations, where the radiosities of
patches are the unknowns and the emissions are the constant terms. In
conventional radiosity all patches are allowed to emit light, i.e. to
be an artificial light source. If we assume that no patch has emission,
we only have to consider daylight. This allows the use of very
efficient solution methods known in numerical mathematics for the set
of equations. The second restriction does not limit the range of
applications too much as well, because in most cases architects are
interested in visualizing their design with daylight conditions.
Details will be described in the final paper.
The new method reduces the computation time of both the radiosity
evaluation and of image generation. Images can be generated at
interactive rates even for very complex scenes, making the method
suitable for walk-throughs and VR-applications. Since numerical
techniques are mainly replaced by analytical formulas, no aliasing
effects appear.
The development of radiosity algorithms for special classes of scenes
is a promising field of future research. Such algorithms are
significantly faster and possibly more accurate than non-specialized
algorithms.

Last update: March 23, 1995. If you have any comments, please
send a mail to *wp#cg.tuwien.ac.at*.
Werner Purgathofer, Institute of Computer Graphics, Technical
University of Vienna.