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 16:08:24 GMT
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Viewed:
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3887 times
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In lugnet.cad, Carl Nelson wrote:
> 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.
Probably. ;^)
> 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?
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
parens, and outside.
Check how I do it in my code. You'll probably have to fetch L3Math.c
and L3Def.h from the ldglite CVS archive on the sourceforge to see
the order, because I think I only put the new stuff in the mirwiz.zip
file.
Don
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Message has 1 Reply:
 | | Re: Quick way to mirror-image a model?
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| (...) It's neither commutative [(a * b) * c != a * (b * c)] nor associative [a * b != b * a]. That shouldn't be the problem in the calculation above, since the current matrix was the identity matrix... (...) Looks like you're doing MF = MP * (MC * (...) (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? [DAT]
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| (...) 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 (...) (20 years ago, 23-Jun-04, to lugnet.cad)
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