Matrixes Theory
===============
Very important to express any rotation for OpenGL.

A very simple and though not too deep introduction, contains also a good Quaternion introduction:
http://skal.planet-d.net/demo/matrixfaq.html

Specialy Matrix Rotations:
http://mathworld.wolfram.com/RotaionMatrix.html

OpenGL Transformation/Rotation Matrixes:
http://nehe.gamdev.net/data/articles/article.asp?article=02


Quaternion Mathematics
======================
Orientations can be represented as Quaternions. They make it simpler and, in tearm of CPU-Time, cheaper to calculate rotations.

A good and understandable introduction can be found here:
http://pw1.netcom.com/~hjsmith/Quatdoc/Qindex.html


www.gamedev.net/reference/articles/article1095.asp