Autodesk LIGHTSCAPE, Manual

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Radiosity Processing 11
174
Lightscape
The illumination contrast is a measure of the varia-
tion in illumination across the given mesh element.
A small contrast (close to 0) between two vertices of
a mesh element indicates an approximately uniform
illumination across the element. A larger contrast
(close to 1) suggests that fine illumination details
may cross the mesh element.
If the illumination contrast of an element is larger
than the value of the Subdivision Contrast
Threshold parameter, the system subdivides the
element into four similar smaller elements and
computes new illumination values for the new mesh
vertices. It then computes the illumination contrast
for the new elements and compares them against the
threshold, possibly causing more subdivisions.
Therefore, decreasing the Subdivision Contrast
Threshold is likely to increase subdivision towards
the minimum mesh spacing limit.
This process continues until the mesh elements are
small enough to accurately reproduce the illumina-
tion of the surface of interest or until the Minimum
Mesh Spacing is reached.
Disable Solution Changes
So that you can change surface materials and light
sources and compensate for the change in illumina-
tion without restarting the solution process from
scratch, the system must undo the effect of one or
more light sources (primary and secondary). The
system undoes the lighting effects by propagating
negative light from the source to the receiving
surfaces, thus removing light from the illumination
of the scene.
During this step it is important that the mesh subdi-
vision be exactly the same as that resulting from the
original positive light contribution from that source.
The system can guarantee this requirement. There is,
however, a cost—it uses a variation of the meshing
scheme that may increase the number of mesh
elements slightly. If you know you will not make any
changes to a solution, you can use the Disable Solu-
tion Changes parameter to obtain a more efficient
result.
Running a simulation with Disable Solution
Changes enabled does not prevent you from later
changing surface materials and light sources.
However, if you do, the system warns you that it may
be unable to compensate for such changes in the
radiosity solution correctly. The system also warns
you when it is unable to refine shadows with the ray
tracer.
Lock Mesh
Enable the Lock Mesh parameter to prevent succes-
sive iterations of the lighting simulation from
subdividing any surface mesh further than the
current configuration.
If this parameter is enabled when you reset a solu-
tion, the system restores all illumination values to 0
while preserving the current mesh subdivision.
This feature is useful only for applications where you
need to preserve the arrangement of the mesh
elements. Generally, you should leave this parameter
off.
Setting Source Parameters
Use the source parameters to control how accurately
Lightscape computes the contribution from a light
source to each of the receiving mesh vertices.
Use the source parameters to independently control
the contribution from direct light sources (lumi-