Applying RenderMap properties to clusters is a useful technique for working with symmetrical texture maps with overlapping UV coordinates. Suppose you have a model of a head. Each half of the head uses the same UV coordinates, but is lit with a different colored light. If you rendermap the entire head, the same part of the texture is sampled for each half, with no indication of which half’s results come out on top. As a result, the two halves’ results are blended together in the resulting surface color map (for example), which is probably not what you want.
To generate a surface color map that includes the correct lighting for each half of the head, you can create a cluster on each half and then rendermap each cluster. When you apply the surface color maps to their respective clusters, each side of the head is textured correctly, with the correct lighting “baked” in. Alternatively, you can combine both surface color maps into a single texture image, apply the image to the head, and adjust the head’s UV coordinates accordingly.
To rendermap a cluster
• You rendermap clusters exactly the same way that you rendermap whole objects. Select a cluster (rather than an object) and apply the rendermap property as described [here].
SOFTIMAGE|XSI v.6.01