Autodesk LIGHTSCAPE, Manual

Page: 181 / 362

Setting the Processing Parameters
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3.
Set the light source parameters in the Source
group box. For information, see “Setting Source Pa-
rameters” on page 174.
4. Set the processing parameters in the Process
group box. For information, see “Setting Process Pa-
rameters” on page 176.
5.
Set the processing tolerance parameters in the
Tolerances group box. For information, see “Setting
Tolerance Parameters” on page 178.
6. Click OK.
Setting Receiver Parameters
Use the parameters in the Receiver group box to
control the meshing of light-receiving surfaces.
The number of mesh elements affects the time and
memory required to compute and display the radi-
osity solution. If the mesh is too coarse, the results
look crude and may contain visual artifacts. If the
mesh is too fine, the visual effect may be
outstanding, but the memory requirements and
calculation time may grow beyond acceptable levels.
It is recommended that you first run a test using a
coarse mesh, then work up to stricter settings over
more tests. This is often the fastest way to achieve the
desired balance between solution quality and
computational resources.
Minimum Mesh Spacing
Subdividing mesh elements based exclusively on
illumination contrast can lead to excessive subdivi-
sion when a sharp shadow boundary crosses a
surface. Use the Minimum Mesh Spacing parameter
to limit the number of mesh elements that can be
created.
The subdivision process cannot create new mesh
elements smaller than the specified value of the
Minimum Mesh Spacing, no matter how high the
illumination contrast.
Note: The size of a mesh element is defined as the
length of its longest side and is displayed in the
current units of the model.
Maximum Mesh Spacing
Lightscape estimates the illumination contrast on a
mesh element by the illumination values at its
corners. If your initial mesh elements are too large, it
is possible that certain illumination features (for
example, a light beam) may be missed.
Use the Maximum Mesh Spacing parameter to set
the initial mesh elements to a size where at least one
corner will capture a light.
Subdivision Contrast Threshold
Rather than meshing a surface using a uniform grid
of mesh elements, the simulation process uses a
more sophisticated adaptive subdivision scheme to
create smaller elements in areas that contain smaller
illumination details (such as shadow boundaries)
and larger elements in areas where the illumination
is fairly constant. This technique allocates
processing resources to the areas of the model that
require them.
The simulation starts by computing the contribution
of the current light source to the vertices of the initial
surface mesh. Then, for each mesh element, the
system compares the values between the darkest and
brightest of its vertices to compute an estimate of the
illumination contrast over the element.