A major part of rendering (making images more realistic) is the visible surface problem, i.e, only display those surfaces which should be visible.

This was one of the major areas of activity in computer graphics and many different algorithms were developed. The algorithms can be divided into two classes:
object space ------------> World Coordinates
image space ------------> PDC Coordinates
Hidden surface Algorithms are usually image space or a combination of object and image space. Below are discussed some of the many visible surface determination algorithms.
Scan Line Graphics Menu
HyperGraph home page.