hi all I'm trying to implement collision detection and resolve for level environment, based on Melax paper "Dynamic Plane Shifting BSP Traversal". http://www.melax.com/bsp/ Even though beveling edges as mentioned in the paper, I still got some unwanted invisible walls. When going down the bsp tree, checking each node/plane for intersection with the player-sphere/cylinder, you check both subtrees of a node/plane "A" colliding with the player. Unfortunatly there is a chance that one of the subtrees holds a plane similar to "A" resulting in a collision and therefore in an invisible wall, even when you did not touch the polygons belonging to that plane. I created some images to illustrate the problem: http://www.freewebs.com/silentbob26/melaxbspinvisiblewalls.htm Any idea what to do about this? This case does not seem to be mentioned in Melax papers, so did I maybe do something wrong?