[Home]History of Radiosity

HomePage | Recent Changes | Preferences

Revision 2 . . September 30, 2001 12:56 am by Levork [Expanded to include description of basic algorithm]
Revision 1 . . September 25, 2001 5:41 am by (logged).224.100.xxx [Factored Radiosity out of Computer-Generated Art]
  

Difference (from prior major revision) (no other diffs)

Changed: 1c1,30
Radiosity is a special technique for 3D computer graphics which computes the "energy" of light for various points in a virtual environment.
Radiosity is a rendering algorithm used
in 3D computer graphics, and was the first (and most popular)
global illumination method. Radiosity was introduced in 1984 by
researchers at Cornell (Goral, Torrance, and
Greenberg) in their SIGGRAPH paper "Modeling the interaction of Light
Between Diffuse Surfaces".

The basic radiosity method has its basis in the theory of
thermal radiation, since radiosity relies on computing
the amount of light energy transferred between two surfaces.
In order to simplify the algorithm, the radiosity algorithm assumes
that this amount is constant across the surfaces; this means that in
order to compute an accurate image, geometry in the scene description
must be broken down into smaller areas, or patches, which can then be
recombined for the final image.

After this break down, the amount of light energy transfer can be
computed by using the known reflectivity of the reflecting patch,
combined with the form factor of the two patches. This
dimensionless quantity is computed from the geometric orientation of
two patches, and can be thought of as the fraction of the total
possible emitting area of the first patch which is covered by the
second patch. Early radiosity methods used a hemicube (an
imaginary cube centered upon the first surface to which the second
surface was projected) to approximate the form factor. Other
techniques have been proposed, including the use of ray tracing.

Radiosity is very computationally expensive, because ideally form
factors must be derived for every possible pair of patches, leading to
an exponential increase in computation with added geometry.

HomePage | Recent Changes | Preferences
Search: