Subject:
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Re: Another matrix inverse question
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Newsgroups:
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lugnet.cad
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Date:
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Tue, 10 Apr 2007 19:29:53 GMT
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Viewed:
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1772 times
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Thanks for the information, everyone. Although the test case I posted was
arbitrary, I did some other tests with matrices that were used for rotations and
translations. The upper-left 3x3 seemed to be OK, but the bottom row had
problems. I'm guessing that the inversion routine wasn't written to include
those.
I wanted the inverse so that I could move a part back to the origin and do
rotations in the local coordinate space. I think that what I will do is keep an
inverse matrix with the transformation matrix, and every time I do a
transformation (like rotate 45 degrees around the X axis) I will do the inverse
(-45 degrees) and apply it to the inverse matrix.
I suppose another possibility is to transform the origin and/or axis of rotation
and then use quaternions to specify rotation around a point other than the
origin, but it seems like that would have more opportunities for mistakes,
considering my limited experience with quaternions.
Thanks again for the help.
Brian Durney
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Message has 1 Reply:
 | | Re: Another matrix inverse question
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| (...) Quarternions are, IMO, a bad way to do what matrices do well. For a rotation you don't need to (and shouldn't) calculate the inverse by a routine. Just transpose (swap the off-diagonals) and you have the inverse. There's no point running (...) (17 years ago, 10-Apr-07, to lugnet.cad)
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Message is in Reply To:
| | Re: Another matrix inverse question
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| (...) Hi Travis, Looking at the java version of your inversion routine I would guess that it will work for almost any 3x3 matrix + 1x3 translation (the 4x3 + 1 form). Where it will have problems is in matrices for which one or more of the (...) (17 years ago, 10-Apr-07, to lugnet.cad)
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