Planar Geometric Projections and Viewing Transformations

Abstract

In computer graphics one is often concerned with representing three-dimensional objects on a two-dimensional display surface. The choice of such a representation depends on several factors, including the purpose for which the representation is intended, the visual effects that are desired, and the shape of the object. This paper describes how twodimensional views can be obtained using planar geometric projections such as perspective and parallel projections. It discusses how these projections can be generated from a threedimensional representation of an object in a manner suitable for computer graphics systems. In particular, it shows how these projections can be generated using the viewing transformations of the Core Graphics System. The factors that affect the choice of projection are also discussed, and some guidelines for making such a choice are given.