Viewing frustum

of a rectangular pyramid (hence the name). The planes that cut the frustum perpendicular to the viewing direction are called the "near plane" and the "far plane". Objects closer to the camera than the near plane or beyond the far plane are not drawn. Often, the far plane is placed infinitely far away from the camera so all objects within the frustum are drawn regardless of their distance from the camera.

Viewing frustum culling or view frustum culling is the process of removing objects that lie completely outside the viewing frustum from the rendering process. Rendering these objects would be a waste of time since they are not directly visible. In ray tracing, viewing frustum culling cannot be performed because objects outside the viewing frustum may be visible when reflected off an object inside the frustum. To make culling fast, it is usually done using bounding volumes surrounding the objects rather than the objects themselves.

Definitions

*VPN - the view-plane normal - a normal to the view plane.
*VUP - the view-up vector - the vector on the view plane that indicates the upward direction.
*VRP - the viewing reference point - a point located on the view plane, and the origin of the VRC.
*PRP - the projection reference point - the point where the image is projected from, for parallel projection, the PRP is at infinity.
*VRC - the viewing-reference coordinate system.