SbViewVolume(3) on Linux
The text fae797b5b3f7, as Debian 6.0 (Squeeze) shipped it.
The SbViewVolume class is a viewing volume in 3D space. This class contains the necessary information for storing a view volume. It has methods for projection of primitives into the 3D volume from 2D points in the projection plane or vice versa, doing camera transforms, view volume transforms, etc.