VBGamer

While this is true, a BSP tree is not very useful for something like a Racing game where there are wide open spaces. (In fairly flat terrain (like a normal racing game), a BSP tree would in fact be the worst possible thing you could use)... By using an Octree or Quadtree system you can do the same "Large Polygon Set Rejection" for visibility and collision detection. Then by simply casting a ray straight down you can check easily the distance between your cars position (or of each wheel if you are planning to implement some physics) you can easily return the distance from that point to the polys plane (if the ray intersects with the poly itself).... There is plenty of information about Octrees and Quadtrees scattered around, Flipcode.com is a good place to start... As for ray casting (look for ray casting, not ray tracing, they are slightly different things) there are plenty of tutorials scattered around too, again CDVG has one <http://francis.dupont.free.fr/coindev/english/ > and I heard Voodoo VB has one, although it's not the most efficient solution, it works well to get you started... Adam