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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Fri, 18 Jun 2004 14:19:22 GMT
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Viewed:
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2476 times
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In lugnet.cad, Carl Nelson wrote:
> In lugnet.cad, Dave Schuler wrote:
> > Dumb, dumb, dumb. To be a true "mirror" as you've requested, the second example
> > should have read this way:
> >
> > A B C D E F G H I J K L M N O P
> >
> > 1 16 -100 0 -10 -1 0 0 0 1 0 0 0 -1 3001.DAT
> >
> > The way I originally posted it, the 3001 brick would be flipped left-to-right,
> > but it would be at the same location as the non-flipped brick.
> >
> > Sorry about that.
>
>
> Wouldn't that still be a 180 degree rotation rather than a flip, since
>
> -1 0 0
> (x y z) * 0 1 0 = (-x y -z)
> 0 0 -1
>
> ?
>
> Or am I laying out my rotation matrix incorrectly (is the first line a b c or a
> d g)?
>
> Sorry for all the stupid questions, I'm still trying to dredge my linear algebra
> out of the dark recesses of my memory.
When you ask a stupid question, I'll let you know! 8^)
You're right--it would rotate the brick 180 degrees, but I think that's
necessary sometimes (like for the 2x2 slope bricks mirrored left-to-right). But
you're also right that this isn't desireable in the case of bricks mirrored
front-to-back. That's where my clunky explanation really breaks down.
You'd probably want to avoid a "flip," because that would cause the stud-logos
to be reversed. I think basically you'll need to rotate some bricks 180 degrees
for the second tower, and you'll simply move other bricks (along the axes from
the first tower's location to the second, without rotating the brick along the
way).
Sadly, I can't help you with the formal matrix rotation or linear algebra--my
understanding of all of this comes from picking at LDraw parts until I get what
I'm looking for...
The more I look at this, the more I see what Dan was saying--this is a
cumbersome method!
Dave!
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Message has 1 Reply:
 | | Re: Quick way to mirror-image a model?
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| (...) Now that I've done that, I agree with you. The true proper thing to do is to adjust the rotation matrix of all parts by -a d -g (x, y, z) * -b e -h = (-ax-by-cz, dx+ey+fz, -gx-hy-iz) -c f -i and create a list of exceptions that would be a (...) (20 years ago, 18-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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| (...) Wouldn't that still be a 180 degree rotation rather than a flip, since -1 0 0 (x y z) * 0 1 0 = (-x y -z) 0 0 -1 ? Or am I laying out my rotation matrix incorrectly (is the first line a b c or a d g)? Sorry for all the stupid questions, I'm (...) (20 years ago, 18-Jun-04, to lugnet.cad)
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