The lines connecting the Camera-GO with the Background-GO denote the edges of the view frustum
(edges of the camera's field of view) of the Camera-GO.
The near and far clipping plane of the virtual camera view frustum
was set to 500 mm and 10500 mm respectively.
In this example, the view frustum
of the user (depicted in red) is also used as a tessellation criterion.
There two type culling suitable to be applied in crowd rendering: view frustum culling and occlusion culling.
There two approaches of view frustum culling (VFC): transform the bounding volume into perspective view  and check the bounding volume against view frustum volume by it six planes .
It will display several functions that can be choose by the user, they either can enable or disable view frustum culling.
Before rendering start, view frustum culling will be used to cull any unneeded objects from the walkthrough system.
The z_near and z_far clipping plane of the virtual camera, view frustum
, were set to 500 mm and 10500 mm, respectively, in order to cover all four 3D scenes used in this experiment.
Research I did at the time suggested that one of the few options was for game developers to explicitly create multiple view frustums
. Most game engines don't do this, since it's difficult and time consuming.