Special:
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[DAT] (requires LDraw-compatible viewer)
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Subject:
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Re: Quick way to mirror-image a model?
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Newsgroups:
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lugnet.cad
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Date:
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Wed, 23 Jun 2004 15:58:08 GMT
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Viewed:
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3820 times
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In lugnet.cad, Steve Bliss wrote:
> Actually, I think they're not - "Steve's algorithm" (ha!) requires that both the
> MP and ME transforms be mirroring, so that the MF transform would be
> non-mirroring.
Can you or Don check my work? I'm trying to figure out why the ME transform
that I did works in my program and the ME that Don put in mirror.ini works in
his code, but not vice-versa. The most likely explanation is that I'm doing
something stupid.
MP matrix (reflection about the plane containing the Z & Y axes):
-1 0 0
0 1 0
0 0 1
MC matrix (current piece value for a 2357 2 x 2 corner brick)
1 0 0
0 1 0
0 0 1
Don's ME matrix for 2357:
0 0 1
0 1 0
1 0 0
MP * MC =
-1 0 0
0 1 0
0 0 1
(MP * MC) * ME =
0 0 1
0 1 0
-1 0 0
which is a 180-degree rotation out from where it should be. What's my error
here?
Thanks,
Carl
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Message has 1 Reply:
 | | Re: Quick way to mirror-image a model?
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| (...) Probably. ;^) (...) Matrix multiplication is not commutative. (distributive? Err, I forget my math terms.) You're doing one or more of the multiplications in the wrong order? Try ME * (MC * MP) instead. Notice I switched the order inside the (...) (20 years ago, 23-Jun-04, to lugnet.cad)
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Message is in Reply To:
| | Re: Quick way to mirror-image a model?
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| (...) Would that work in general cases, or just for right-left reflection? (...) Actually, I think they're not - "Steve's algorithm" (ha!) requires that both the MP and ME transforms be mirroring, so that the MF transform would be non-mirroring. (...) (20 years ago, 23-Jun-04, to lugnet.cad)
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