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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Wed, 4 Oct 2000 21:23:21 GMT
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Viewed:
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582 times
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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 happen to know how to do that as well?
It's been such a long time, I've forgotten way too much of this stuff.
Don
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.
In lugnet.cad.dev, Steve Demlow writes:
> Don Heyse <dheyse@hotmail.spam.go.away.com> wrote:
>
> > Wherever they came from, they don't seem to be pure rotation matrices
> > fit for a viewing transformation. When I multiply one of these with
> > another rotation matrix the model starts to look sheared.
>
> I don't know their origin, but you're right, there's a shear component in
> them. Here's what a matrix decomposition shows:
>
> > Oblique=1,0,1,0.5,1,-0.5,-1,0,1
>
> Scale : (1.5, 0.942809, 1.41421, 0)
> Rotate : (0.321751, 0.729728, 0.463648, 0)
> Translate : (0, 0, 0, 0)
> Shear : (0.353553, -0.117851, -0.333333, 0)
>
> > UpsideDown=-1,0,1,-0.5,-1,-0.5,1,0,0
>
> Scale : (1.5, 0.942809, 0.707107, 0)
> Rotate : (-0.321751, -0.729728, -2.67795, 0)
> Translate : (0, 0, 0, 0)
> Shear : (0.353553, -0.707107, 1, 0)
>
> > Natural=0.625,0,1.075,0.5375,1.25,-0.3125,-1.25,0,2.5
>
> Scale : (1.49734, 1.16669, 2.07954, 0)
> Rotate : (0.622665, 0.987793, 0.710271, 0)
> Translate : (0, 0, 0, 0)
> Shear : (0.384604, -0.841771, 0.162744, 0)
>
> (Note for purists: I'm not even sure I used the right matrix orientation to
> get the above results, but there's a shear component in there either way.)
>
> I look forward to the next update of ldglite - very useful program!
>
> Steve
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Message has 1 Reply:
 | | Re: Unusual View matrices in LDRAW.INI
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| (...) It's from Graphics Gems II, the code for which is available online (linked from (URL) ). (...) 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 (...) (24 years ago, 5-Oct-00, to lugnet.cad.dev)
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Message is in Reply To:
| | Re: Unusual View matrices in LDRAW.INI
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| (...) I don't know their origin, but you're right, there's a shear component in them. Here's what a matrix decomposition shows: (...) Scale : (1.5, 0.942809, 1.41421, 0) Rotate : (0.321751, 0.729728, 0.463648, 0) Translate : (0, 0, 0, 0) Shear : (...) (24 years ago, 4-Oct-00, to lugnet.cad.dev)
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