Subject:
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Re: Mirror matrix question
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Newsgroups:
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lugnet.cad
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Date:
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Thu, 13 Aug 2009 10:03:08 GMT
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Viewed:
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9774 times
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In lugnet.cad, Kevin L. Clague wrote:
> Hi gang,
>
> If I have an LDraw Type 1 line that adds a submodel, and the rotation matrix
> of the line is a mirrored matrix about one and only one axis, can one calculate
> which axis the model is mirrored about? Can one do so if the user mirrored
> *and* rotated the submodel when adding it to the model?
>
> What I want to do is to be able to render the mirror image version of the
> model as the mirror image (so the user builds the submodel correctly), but with
> the same overall orientation as the non-mirrored version.
>
> Any help would be great.
>
> Thanks,
> Kevin
Hi Kevin,
I just realised that there might be a way to do this by exploiting the way LDRAW
defines parts. All mirrored parts should be written as a bunch of studs and a
subpart which is either mirrored or non-mirrored. By determining which part is
the mirrored version you can use the applied rotation matrix and the internal
mirroring matrix to work out the correct orientation.
So let us assume the unmirrored part is defined by
studs + R x subpart
and the mirrored part is defined by
studs + Rp x subpart (where Rm has a negative determinate)
while the mirrored submodel including the part is acted upon by a mirror matrix
M
If we mirror the unmirrored part then the submodel is rotated to M R and thus we
must set Mp = M R inv(Rp) when we replace it by the mirrored part
If we mirror the mirrored part then the submodel is rotated to M Rp and thus we
must set Mp = M Rp inv(R) when we replace it by the unmirrored part
Does this all make sense?
Tim
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Message is in Reply To:
 | | Mirror matrix question
|
| Hi gang, If I have an LDraw Type 1 line that adds a submodel, and the rotation matrix of the line is a mirrored matrix about one and only one axis, can one calculate which axis the model is mirrored about? Can one do so if the user mirrored *and* (...) (15 years ago, 14-Jun-09, to lugnet.cad)
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