Path: chuka.playstation.co.uk!scea!peter_alau@playstation.sony.com
From: jamin1@psu.edu (Jamin Frederick)
Newsgroups: scee.yaroze.programming.3d_graphics
Subject: Re: RotMatrixBUG????
Date: Thu, 09 Jul 1998 21:23:38 GMT
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On Thu, 09 Jul 1998 08:20:01 +0100, Peter Passmore
<p.passmore@mdx.ac.uk> wrote:

>Just storing the vector does not store the
>order and depending on your sequence of rotations you can end up with
>the situation that Emmanele describes as his first problem, the object
>does not rotate around it's own axes. 
>

That makes pretty good sense.  Are you and James saying something
else, though, because he just said that this was doable with a lone
vector.  Is it *possible* to use a vector to store this info? 


Maybe I'm getting confused on this issue:

Suppose I have a plate, centered at the local origin, circular around
the xz plane (this will be in Sony coords).  Now I will rotate it
along the z axis, so it is now tilted, partly above the xz plane and
partly below.  Now, if I rotate it around y (vertically), does this
mean it will spin in a circle, planar with the flat of the plate, or
will it go around parallel to the world y axis?  

I was assuming that the whole local coordinate system rotates with the
object (the local coordinate axis will be "stuck" to the plate, and
wherever it moves or rotates, it does too), so that further rotations
are now with respect to this new orientation, and the plate should
rotate in a circle.

So shouldn't I be able to accrue these rotations, if the local
coordinate system is indeed doing this -- just keep adding amounts to
the current (a,b,c) angular vector, which represents positive angles
from the original orientation.  I have tried this (using RotMatrix to
turn the vector into a matrix), and get the funny results, though.

Jamin