Subject:
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Re: stl2dat conversion tool beta2
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Newsgroups:
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lugnet.cad.dev
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Date:
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Tue, 15 Feb 2000 15:12:17 GMT
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Viewed:
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1518 times
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On Mon, 14 Feb 2000 20:06:37 GMT, Rui Martins <Rui.Martins@link.pt>
wrote:
[SNIP]
> > In fact, I measure the angle between the normal of the face, but the
> > result is the same.
>
> Iep, but the valid values for the angle differ.
What do you mean ? Isn't a = b ?
\ b|
\ |
_ _ _______face
a /
/
/face
/
> > The bug was because I have a step where I replace two triangles by a
> > thrid. This step caused vertex suppressions. I moved this step after
> > the edges have been created.
> > 1
> > /|\
> > 2-3-4
> >
> > to
> >
> > 1
> > / \
> > 2---4
>
> See my previous reply about merges !
The merging is done only for strict coplanar and adjacent facets, and
the removed vertex must be on the merged line. In this case vertex[3]
must be on line [2,4].
> > > If an Edge belongs to a sigle triangle then it's a
> > > NORMAL LINE
> > This case can never happend in STL files. The solid must be entirely
> > closed. An edge has always two adjacent facets.
>
> I don't think so !
> Where have you read that a .STL file must have a closed solid ?
>
> This would make no sense either.
> Also in my CAD program, I can define open surfaces, and I can then save
> them to .STL files.
I was told by a person who works in rapid prototyping. And in my cad
program I cannot save open surfaces so I thought this nevers occurs in
STL files.
I will add this case in my program. It should not be difficult.
[SNIP]
> > In future version, I will extend this merge to quad more than two
> > triangles.
>
> Always remember what I have said in the previous reply.
When I talk about facet merging, it is a final process. After the
creation of edges is done, the program looks if it can remove useless
vertices. In this step facets can be taken independtly from each
other, beause dat format handles them independtly.
In the STL file, there is someting like :
1-----2
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3-----4-----5
| / \ |
| / \ |
6-----------7
it becomes in DAT file :
1-----2
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3-----4
3-----------5
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6-----------7
Again, the merging is done only for strict coplanar and adjacent
facets, and the removed vertex must be on the merged line. In this
case vertex[4] must be on line [3,5].
The same checks is done for merging edges.
1----2----3
can be merged to
1---------3
Only if vertex[2] is on line [1,3]
Marc Klein
A Mindstorms fan.
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Message has 1 Reply:
 | | Re: stl2dat conversion tool beta2
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| (...) What I mean is : _ _ _______face a /b / /face / In that to apply a optional line you have: : (a) must be BIGGER tha (45) but : (b) must be LESSER than (90+45) Assumming both angles are positive, and that 45 is the reference angle we talk about (...) (25 years ago, 15-Feb-00, to lugnet.cad.dev)
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Message is in Reply To:
| | Re: stl2dat conversion tool beta2
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| (...) This should be one of your top priorities, since unwanted data only slows down the rendering programs. (...) Iep, but the valid values for the angle differ. (...) See my previous reply about merges ! (...) I don't think so ! Where have you (...) (25 years ago, 14-Feb-00, to lugnet.cad.dev)
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