3D Graphics - Game Programming Algorithms and Techniques - page 89

The orthographic projection matrix is composed of four parameters: the width
and height of the view, and the shortest distance between the eye and the near/far
planes:
The perspective projection has one more parameter, called field of view (FOV).
This is the angle around the camera that is visible in the projection. Changing the
field of view determines how much of the 3D world is visible, and is covered in
more detail in Chapter 8 , “ Cameras .” Add in the FOV angle and it is possible to
calculate the perspective matrix:
There is one last thing to consider with the perspective matrix. When a vertex is
multiplied by a perspective matrix, its w-component will no longer be 1. The per-
spective divide takes each component of the transformed vertex and divides it by
the w-component, so the w-component becomes 1 again. This process is actually
what adds the sense of depth perception to the perspective transform.