Subject:
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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 13:56:10 GMT
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Viewed:
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577 times
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Hey, does anybody out there know the origin of the "Oblique",
"UpsideDown", and "Natural" viewing matrices in LDRAW.INI. I'm not
sure whether these came from LDAO, LDLITE, or perhaps even LDRAW?
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. Is there a
projection transform in there or are they just plain wrong? I believe
someone previously mentioned that there was something unusual about
these matrices but I can't remember what.
Anyways, the point is I finally got that pesky mouse-drag model
spinning trick to work in ldglite but I had to replace these three
view matrices to do it.
Also I noticed at one point that L3LAB seemed to shear the model
sometimes during spinning. Does/Did it perhaps use the view matrices
from LDRAW.INI as well?
Here are the original matrices.
Oblique=1,0,1,0.5,1,-0.5,-1,0,1
UpsideDown=-1,0,1,-0.5,-1,-0.5,1,0,0
Natural=0.625,0,1.075,0.5375,1.25,-0.3125,-1.25,0,2.5
Here are the replacement matrices.
Oblique=0.707104,0,0.707104,0.353553,0.866025,-0.353553,-0.612372,0.5,0.612372
UpsideDown=0.707104,0,0.707104,-0.353553,-0.866025,0.353553,0.612372,-0.5,-
0.612372
Natural=0.5,0,0.866025,0.433013,0.866025,-0.25,-0.75,0.5,0.433013
My Oblique matrix is a 45 degree rotation about y followed by 30 about x.
My UpsideDown matrix is a 45 degree rotation about y followed by 210 about x.
My Natural matrix is a 60 degree rotation about y followed by 30 about x.
Don
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Message has 3 Replies:
 | | 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)
| | | Re: Unusual View matrices in LDRAW.INI
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| I believe the matrix happens to produce a standard isometric view, but doesn't do so in the traditional 3D graphics way of rotation. This means that in addition to not looking right after rotation, it also doens't produce correct results when you (...) (24 years ago, 4-Oct-00, to lugnet.cad.dev)
| | | Re: Unusual View matrices in LDRAW.INI
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| (...) LDAO writes those entries to ldraw.ini. I'm not sure if any other programs update that section or not. The "Oblique" view is the default view for LDraw, and was also used for LDLite (I think) and L3Lab. "UpsideDown" is derived from "Oblique". (...) (24 years ago, 4-Oct-00, to lugnet.cad.dev)
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