Sure. As far as I know, a heightmap takes a grayscale bitmap and makes a 3d like model of it. White is higher areas, black is lower. So you don't have true 3d (which is why I'm asking if it can be done in ZDoom) but you have the map split into triangles to make hills and stuff. If you have played any new games, they have heightmaps. FarCry, probably Doom3 in the outdoor parts, UT2004, and others. It makes it easier to make realistic outdoor environements without drawing every triangle by hand. Does that help?