While looking at some Half-Life models, I saw that they used OBB''s. Does anyone know if Valve uses them as is for collision detection, or do they actively degenerate them into AABB''s using the OBB''s corners as extreme points? I was considering allowing my modeling system to use models that have vertices "grouped" together into bounding sphere groups. Then, for each frame, I precalculate the minimum bounding sphere that would enclose all the points tagged. Then, as I transition smoothly transition between key-frames, I smoothly transition the bounding spheres as well. Is it worth considering, or am I barking up the wrong tree? C=64