
“This tutorial shows a method for generating FinalGather like ambience using the XSIAmbientOcclusion and the Lightmap Color_Sampler shader in XSI. The basic idea behind this, is to create faster and non-flickering (animation) renderings. Unfortunately this method is not as accurate as FG and doesn’t support multiple bounces.”
http://www.3dtotal.com/team/Tutorials/lightmap/lightmap01.php