Subject:
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Re: Unusual View matrices in LDRAW.INI
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Newsgroups:
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lugnet.cad.dev
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Date:
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Thu, 5 Oct 2000 23:56:42 GMT
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Viewed:
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978 times
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Don Heyse <dheyse@hotmail.spam.go.away.com> wrote:
> I knew there was a way to decompose the matrices! But I couldn't find it.
> Where is that written down?
It's from Graphics Gems II, the code for which is available online (linked
from http://www.acm.org/tog/Software.html ).
> I also thought there was a way to remove the
> cumulative round off errors in a transformation matrix after many matrix
> multiplications. Do you happen to know how to do that as well?
That's called (re-)orthogonalization. Graphics Gems I has code to do it.
You might also reconsider whatever it is that's causing the matrix to become
nonorthogonal. In the case of arcball-type rotation you can:
1. Store the current transform matrix M when the rotation begins
2. Store the initial arcball conditions (cursor location, etc.)
3. For each mouse movement, compute the transform M' from the original
location to the current one - that is, don't use incremental updates
4. Multiply M and M' to get the rotated transform, and apply it to the object
5. When done, update M to M * M'
I've been using the Gems arcball code in this manner for years and have
never had to deal with orthogonalization.
> PS. I might do a new ldglite release this weekend. Lots of bug fixes
> and I tried to add some more of the missing ldlite features.
Cool!
Steve
--
Barb & Steve Demlow | demlow@visi.com | www.visi.com/~demlow/
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Message is in Reply To:
 | | Re: Unusual View matrices in LDRAW.INI
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| I knew there was a way to decompose the matrices! But I couldn't find it. Where is that written down? I also thought there was a way to remove the cumulative round off errors in a transformation matrix after many matrix multiplications. Do you (...) (24 years ago, 4-Oct-00, to lugnet.cad.dev)
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