Path: chuka.playstation.co.uk!news
From: "Jon Prestidge (alias Moose)" <zmoose@premier.co.uk>
Newsgroups: scee.yaroze.programming.3d_graphics
Subject: Matrices
Date: 12 Jun 1997 11:17:35 GMT
Organization: PlayStation Net Yaroze (SCEE)
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Hello,

I'm just reading-up on matrices before wading in and trying to write some
3D stuff.   I written 3D graphics programs before - but I've done it purely
through using trigonometry - so using matrices is a new ball game for me. 
So if anyone could clear-up the following couple of points that are
perplexing me somewhat I'd be very greatful....

All the books and source-codes I've looked at so far (except Yaroze stuff)
seem to use 4x4 matrices for 3D work, where as the only structure (ie
MATRIX) used in the Yaroze stuff is a 3x3 matrix.  Why?  However I've
noticed that in most examples in books where 4x4 matrices are used
(translating,scaling,rotating etc), the last row and column seem largley
redundant - is this anything to do with it?... or what?

Also what's this Unit Matrix (GsIDMATIX) all about... is it just an ID
matrix as the name might suggests?   I can't find any significant mention
of it in the manual.   Is the Unit Matrix mentioned in the Library
Reference Manual for the GsInitCoordinate2 routine (page 123 in my copy)
the same as GsIDMATRIX? 

Cheers,
 Jon