I'm using this formula for my quaternion camera in OpenGL. It works perfectly but I didn't understand how it was derived. Can anyone here teach me how did the conversion was derived? or maybe give me a book that teach how it is done. Most of the site I found on the net was just showing the equation without showing how it was derived. http://img502.imageshack.us/img502/3771/matrixn.jpg" [Broken] Source: http://www.euclideanspace.com/maths/geometry/rotations/conversions/matrixToQuaternion/index.htm"