The first thing I should clear up is that the shapes and sizes of the pass-through sectors should be identical. This would make ray casting between the sectors much easier as 5x-6y on the celing sector equals 5x-6y on the floor sector.<br>Now, the scene is rendered from the POV of the players eyes right? That would be a specific map co-ordinate, hight, direction facing, and angle. There would come a point where the players hight equals the ceiling's hight, and in reality the player would be bumping thier head on our fake celing. But since we've marked the ceiling as a pass-through, all the engine has to do is change the players map co-ordinates to the other sector, change the player's hight value to the floor, and update the automap. That takes care of the visual aspect. Now for the players feet, since he might still have some steps to climb before he passes completely into the other sector. In this case, another POV is spawned in the original sector at floor level to represent the player's feet. This POV does not need to be graphically implemented....it only needs to cast rays out to see of the player's feet have bumped into anything. Once the player's feet POV passes into the other sector, it is released and the game continues like normal. This feet POV also might make it easier for the engine to detect the player's position in the view of another player. As far as shooting is concerned....well, isn't shooting just another form of ray casting? If it is, the bullet ray could pass through our special ceiling/floor texture as easily as a visual ray. In the reverse, monster ai sight lines could be programmed to pass through and detect the player. <br>I'm basing my ideas on things I've read about ray casting in a slightly old book on 3d game programming, which told me ray cating was the technology that DOOM and it's clones used. Please let me know if Vavoom uses some other kind of technology.