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 16:00:47 GMT
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Viewed:
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2956 times
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In lugnet.cad, Dave Schuler wrote:
> 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).
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 rotation matrix plus a
translation, for example a 2 x 2 corner reflected on a horizontal axis should be
rotated by:
0 0 -1
0 1 0
-1 0 0
giving (x' = -z, y' = y, z' = -x)
and then translated in X and Z axes to put it in the right place.
Basically that would mean that any part having a rotation point not at its
geometric center would need a custom rotation and translation.
> 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...
Don't worry--I actually have a math degree and did most of my work in linear
algebra & analytical geometry and, um, it took far longer to understand this
than I care to admit...
> The more I look at this, the more I see what Dan was saying--this is a
> cumbersome method!
Ah, it's not too bad, especially when I did my program to automate it. It has
shortcomings, but it works for the majority and the rest is merely exception
processing.
Carl
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Message has 1 Reply:
 | | Re: Quick way to mirror-image a model?
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| (...) Take a peek at the MLCAD.INI file for minifig posing. Could you use a config file like this to handle the exceptions? I'd imagine if you pick one axis for mirroring that works best with most parts, (I think Travis said most were symmetric (...) (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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| (...) 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 (...) (20 years ago, 18-Jun-04, to lugnet.cad)
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