Subject:
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Re: rotation matrices
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Newsgroups:
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lugnet.cad.dat.parts
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Date:
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Wed, 18 Oct 2000 14:43:34 GMT
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Viewed:
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757 times
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In lugnet.cad.dat.parts, Travis Cobbs wrote:
> 1 <COLOR> X Y Z A B C D E F G H I part.dat
>
> becomes:
>
> A D G X
> B E H Y
> C F I Z
> 0 0 0 1
>
> (Note the letters go vertically.) I believe some references may swap the
> rows/columns, to produce:
>
> A B C 0
> D E F 0
> G H I 0
> X Y Z 1
I'm pretty sure that should be:
A D G 0
B E H 0
C F I 0
X Y Z 1
So multiplying (used fixed-pitch font for proper viewing):
(x y z 1) (A D G 0)
(B E H 0)
(C F I 0)
(X Y Z 1)
gives
(Ax + By + Cx + X Dx + Ey + Cz + Y Gx + Hy + Iz + Z 1)
> It's easy to tell which matrix they are referring to by checking out where
> the translation (X, Y, Z) portion fits into their matrix. Having mapped
> LDraw models to OpenGL, I can say that any OpenGL-related texts will likely
> use the first matrix.
Interesting. I've usually seen the second format (X Y Z on the bottom).
Then again, my main reference is a 15-year-old copy of Foley/Van Dam.
Steve
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Message has 1 Reply:
 | | Re: rotation matrices [DAT]
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| (...) Are you really sure? cause I looked at this file from Fredrik Glockner as an example about the studs to ad in the beginning and end of my curve and it says: 1 16 -90 40 0 0 5 0 -1 0 0 0 0 1 STUD3A.DAT 1 16 20 0 -90 0 0 1 1 0 0 0 5 0 (...) (24 years ago, 19-Oct-00, to lugnet.cad.dat.parts)
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Message is in Reply To:
| | Re: rotation matrices
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| "koen" <koen.jordens@studen...ven.ac.be> wrote in message news:G2JIF8.L7o@lugnet.com... (...) They are the upper-left 3x3 matrix of a standard 4x4 transformation matrix used in 3D graphics. I'm not going to give a lesson on 3D transformations, but (...) (24 years ago, 18-Oct-00, to lugnet.cad.dat.parts)
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