Say I have an octree and at a certain level I store VBOs in that octree. I know the dimensions of of the nodes that own the vbo so I can do basic frustum culling. That works nicely because everything outside of the screen is never rendered.
However my world is quite big and I currently also draw things behind already drawn octrees. What would I use to not draw nodes that are occluded by other nodes and how would I go about that?
I saw some mentions of occlusion culling in the OpenGL superbible but I fail to see how I can utilize that when I don't have a clear distinction between occluders and occludees.