and Rendering System
Gregory J. Ward / GJWard@lbl.gov
The original goals for the
system were modest, or so we thought.
The idea was to produce an accurate tool for lighting simulation
and visualization based on ray-tracing.
Although the initial results were promising, we soon learned that
there was much more to getting the simulation right than plugging
proper values and units into a standard ray-tracing algorithm.
We needed to overcome some basic shortcomings.
The main shortcoming of conventional ray-tracing is that diffuse
interreflection between surfaces is approximated by a uniform
For many scenes, this is a poor approximation, even if the ambient
term is assigned correctly.
Other difficulties arise in treating light distribution from
large sources such as windows, skylights, and large fixtures.
Finally, reflections of lights from mirrors and other secondary sources
These problems, which we will cover in some detail later,
arose from the consideration of our system
design goals, given below.
The principal design goals of
These goals reflect many years
of experience in architectural lighting simulation;
some of them are physically-motivated, others are user-motivated.
All of them must be met before a lighting simulation tool can be of
significant value to a designer.
- Ensure accurate calculation of luminance
- Model both electric light and daylight
- Support a variety of reflectance models
- Support complicated geometry
- Take unmodified input from CAD systems