• clipping objects which will not project onto the image
• restricting the domain of z for visibility calculations

An orthographic view volume:

Clipping operations could be carried out directly based upon the view volumes defined, but is simpler using a canonical view volume. The coordinate system is referred to as the normalized device coordinate system or NDCS.

OpenGL Canonical View Volume

The transformation from VCS to NDCS can be conveniently viewed as part of the projection transformation, as we shall see shortly.

Viewport Transformation

• NDCS to DCS
• simple translate and scale