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From: vlg@fctunl.rccn.pt (Vicente Luis Gracias)
Newsgroups: comp.graphics
Subject: Rotational matrices
Message-ID: <VLG.90Aug8124538@hal.fctunl.rccn.pt>
Date: 8 Aug 90 11:45:38 GMT
Sender: news@fctunl.rccn.pt (USENET News System)
Distribution: comp
Organization: Universidade Nova de Lisboa -- Lisbon, Portugal
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       Does anybody know how I can determine the description of
rotations given a rotational matrix? That is, for example, given a
matrix M that is ONLY composed by rotations on the X, Y or Z axis, how
can I determine each of the rotations (e.g. M = (RotZ a)(RotX b)...)?
There is more than one solution for the equation, but for my case any
one of the solutions is enough. I have tried "extracting" a rotation
on X by an angle that satisfies some conditions, then on Y and then on
Z, cyclically until I get an identity matrix. But this does not always
work and sometimes it loops infinitely. Also the composition of
rotational matrices is not commutative,so RotX.RotY.RotX <> RotX.RotX.RotY.

                                                     Thanks,
                                                            Vicente