Subject:
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Re: LPub4 Alpha3 available
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Newsgroups:
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lugnet.cad
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Date:
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Sat, 28 Jun 2008 03:26:59 GMT
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Viewed:
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6706 times
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In lugnet.cad, Travis Cobbs wrote:
> In lugnet.cad, Tim David wrote:
> > In lugnet.cad, Kevin L. Clague wrote:
> > SNIP
> > >
> > > Are any of the matrix coefficients negative?
> > >
> > > Kev
> >
> > Had a look and yes. I'n not sure quite why though, the sub model in question
> > consists of 2 headlight bricks side by side with a 1x2 grill tile across the two
> > side studs. It is used with the grill facing out on both sides of a train it
> > could be considered a mirror but at the same time it is also just a rotation.
>
> Actually, the matrix can have negative coefficients without being a mirror. If
> I remember correctly, mirror detection is a matter of checking if the
> determinant of the matrix is positive or negative. If the determinant is
> negative, then the matrix is a mirror matrix.
>
> --Travis
You remember correctly. A 90 or 270 degree rotation will have a negative and
positive coefficient off the diagonal while a 180 will have two negatives on the
diagonal.
Tim
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Message is in Reply To:
 | | Re: LPub4 Alpha3 available
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| (...) Actually, the matrix can have negative coefficients without being a mirror. If I remember correctly, mirror detection is a matter of checking if the determinant of the matrix is positive or negative. If the determinant is negative, then the (...) (16 years ago, 28-Jun-08, to lugnet.cad)
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