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From: gavin@krypton.sgi.com (Gavin A. Bell)
Newsgroups: comp.graphics
Subject: Re: 3D Animation Source Code Wanted
Keywords: 3D animation C code wireframe
Message-ID: <2389@odin.SGI.COM>
Date: 3 Jan 90 18:43:24 GMT
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fayne@tellab5.TELLABS.COM (Jeffrey Fayne) writes:

>The biggest problem I'm having is that all the rotation texts I've seen
>assume that the rotations are based on the viewers viewpoint and not the
>objects (ie.  I can rotate an object (say an airplane with the nose
>pointing away from the viewer) and apply rotations (yaw, roll and pitch)
>...

Yaw, roll, pitch isn't a very good way of representing rotations; it
has been likened to representing points on the surface of the earth in
a cartesian coordinate system, instead of the natural spherical
coordinate system (you can do it, it just makes the math big and hairy
and hard to deal with).

A much better way is to use what are variously called 'Quaternions' or
'Euler paramaters' (yaw/pitch/roll is a set of 'Euler angles'; not the
same as Euler paramaters).  They are easy to put into a rotation
matrix and are fairly easy to keep numerically stable (important if you
will go through several thousand or million incremental rotations).

See these references for more info:

Shoemake, Ken, "Animating Rotation with Quaternion Curves," _Computer
Graphics_, 19(3), 245-254, SIGGRAPH Conference Proceedings, July 1985.
	-- has a very nice bibliography.

Kane, Thomas R., Likins, Peter W. and Levinson, David A., _Spacecraft
Dynamics_, McGraw-Hill, Inc. (1983).
	-- quite straightforward, it is easy to adapt the formulas given
to working code.

--gavin