Subject:
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Re: LD-Lite Rotation Matrices?
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Newsgroups:
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lugnet.cad
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Date:
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Wed, 8 May 2002 20:12:23 GMT
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Viewed:
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908 times
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Actually I have a very similiar question.
I originally had a similiar problem in that LDraw in inherently
a Left Handed coordinate system, and my rendering engine needs
right handed coordinates.
I've figured out a solution that works for me so far, but I
a.) don't totally understand why it works.
b.) wonder if I still might have problems that I haven't found yet.
Originally to convert the coordinates, I was just multiplying
the Y coords by -1. This fixed almost everything. The model was
turned right side up, and all looked well.
Until that is I started trying parts that had some of the primitives
rotated about the Z or X axis (instead of just the Y axis) These
tended to rotate the 'wrong' way.
I solved this by multiplying some of the numbers in the transform
matrices in the type 1 lines by -1(I had already been 'fixing' the
Y translation coords here also.)
Specifically I changed a matrix like:
1 2 3 1 -2 3
4 5 6 into -4 5 -6
7 8 9 7 -8 9
(these 4 numbers are the +/-sin(a) values for rotation about X and Z)
I think I understand why it helps (flipping the sign of the sine
would tend to represent a rotation in the other direction.) but I
don't understand why I don't need to do the same to the cos(a) values
in the matrix? Not that I'd know how to if I did, because they tend
to share spaces in the matrix with other cos(a)'s and the scale values.
Is there anything else I need to change do you think?
I'm also wondering if I couldn't just leave all these alone when I
load the geometry and just stick one transform at the top like
1 0 0 1 -1 1
0 -1 0 or maybe -1 -1 -1 or something like that????
0 0 1 1 -1 1
-Kyle
--
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-------------------------------ooO( )Ooo-------------------------------
Kyle J. McDonald (o o)
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(o o) kmcdonald@BigFoot.COM
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Message is in Reply To:
 | | Re: LD-Lite Rotation Matrices?
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| (...) Maybe this is it? l3glite -v3 -a1,0,-1,0.5,-1,0.5,-1,0,-1 file.dat Don (23 years ago, 8-May-02, to lugnet.cad)
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