In order to visualise the visibility within a certain perimeter I use six RTT cameras that concurrently render the scene from a given observation point. When I activate the RTT cameras, the time needed for culling increases tremendously reducing the frame rate.
I first thought that it is because I use six cameras simultaneously, so I only used one camera at a time, choosing another one each frame. Still same issue occurs.
I also tried to identify which camera causes the problem. However, when I only use one camera the whole time, i.e. no change in subsequent frames, the issue disappears.
Does somebody have an idea, what might cause this problem?
I asked because: if the culling time increases linearly with each camera you add, then your logic for switching on one camera at a time per frame is probably not working properly.
It looks like you are doing a viewshed analysis. Since you know the maximum distance, one way to speed up culling would be to force a far clipping plane on the RTT cameras instead of letting OSG automatically calculate it.