I have experimented with graphic engines using multiple kinds of visibilit algoritms, particulary bsp trees and octrees. Therefor I desided to try making one that both uses a bsp tree and an octree. This resulted in me having to lists of faces. One with faces that the bsp tree (indoor) and one that the octree (outdoor) had generated. Knowing if you are indoors or outdoors do anyone know if it is possible to run a check what faces are visible. Kind of like if you are indoors another visibility algorithm determins what faces that are outdoors are behind the indoor faces and so on and now: do anyone know what is the fastest, a single bsp tree, an octree, a combination of a bsp tree and an octree or a combination of a bsp tree and a cell engine or a combination of a bsp tree a cell engine and an octree?
Well…if you’re going to have an indoor/outdoor scene,why not just use an Octree? That’s what I did and it works fine.Using an octree I can detect which polys are visible every frame and this avoids the whole switching between bsp and octree all the time.
I’m just ranting but ,hey,it worked for me 
You could also use portals between the indoor
and the outdoor, and have each side of each
portal point to the data to render on the
other side if it’s visible – including which
kind of tree to use to render.
But, still, I don’t see why you need two
different kinds of trees necessarily. Profile
your code and see which way works the best.
I tried to use the portals and it worked very well, the engine became a little more effective.