In his
answer Tessellator pointed you to an 8-page discussion on quaternions.
Here you've been given further pointers.
Yet you come back, with a triple cross-post, no less, while
QuakeII's source code is available for you to see, if only you'd look.
Edited by - Fruny on February 21, 2002 10:23:24 AM
"Debugging is twice as hard as writing the code in the first place. Therefore, if you write the code as cleverly as possible, you are, by definition, not smart enough to debug it." — Brian W. Kernighan