I've read a little about Portal engines and even less on BSP trees. When I first read about portal engines, it seemed that sectors were usually used to contain rooms, for example, and portals for doors and windows. But the more I read, the less this seemed to be true. Can people comment on this? Also, does anyone know of any good resources for learning (to the level of being able to implement one if so desired) about portal engines and BSP trees? I've read that portal engines are good for indoor games, but are they better than BSP trees for indoor scenery? I guess I'm asking a question that may not have a real answer and will ultimately come down to "It depends on your game." Any help would be appreciated.