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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Mon, 14 Feb 2000 20:06:37 GMT
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Reply-To:
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rui.martins@link.pt^IHateSpam^
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Viewed:
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3402 times
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On Mon, 14 Feb 2000, Marc Klein wrote:
> On Fri, 11 Feb 2000 20:29:56 GMT, Rui Martins <Rui.Martins@link.pt>
> wrote:
>
> > Maybe You should allow the use of the abs() function to be optional,
> > because if the face normal are correctly calculated (the faces are well
> > defined, CCW or CW) you can check the correct value, and NOT the absolute
> > value.
> The normal is explicitely given in STL files.
>
> > I think there are some situations in which this would create unwanted
> > optional lines.
> >
> > Example suppose a 'kind of cylinder' with this form
> > ---------
> > \ /
> > \ /
> > | |
> > / \
> > / \
> > --------
> >
> > You should correctly generate vertical (concentric with the cylinder
> > center) optional lines, but you should NOT generate horizontal optional
> > lines, which I think your current algo does.
> >
> > The vertical eventually will define the silhuete, but the horizontals
> > never will.
>
> Yes. I have planed to optimize this point. I think it is the same case
> for internal cylinders. The angle must be convex and not concav.
> However, it is not done yet.
This should be one of your top priorities, since unwanted data only slows
down the rendering programs.
> > How do you measure the angle ?
>
> I use case 1:
> _ _ _______face
> a /
> /
> /face
> /
> 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.
> > > I have to improve it so it check also partial adjacent facets.
>
> 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 !
> > 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.
> > Else /* Connects two triangles */
> > calc angle between the two triangles
> > if (angle near 0 ) /* they are coplanar */
> > NO LINE
> > elsif (angle optional test)
> > OPTIONAL LINE
> > else
> > NORMAL LINE
>
> > About new Ideias
> > You could make also an option to recreat the quads which once whore
> > quads, you would have to check for this, and if possible, create quads.
>
> I do no understand what you mean with "which once whore quads". In STL
> files they are no quads, only triangles. There is a step in the
> algorithm where two adjacent triangles are merged to one quad.
That was what I meant, because in the application where you modeled the
part, possibly there were quads, which once translated into tris generate
two coplanar tris, when saving as an .STL file.
> In future version, I will extend this merge to quad more than two
> triangles.
Always remember what I have said in the previous reply.
> I will also made option to swith on/off all features of the program,
> plus some extra functions usefull for debug.
>
> Marc Klein
> A Mindstorms fan.
See ya
Rui Martins
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Message has 1 Reply:
 | | Re: stl2dat conversion tool beta2
|
| On Mon, 14 Feb 2000 20:06:37 GMT, Rui Martins <Rui.Martins@link.pt> wrote: [SNIP] (...) What do you mean ? Isn't a = b ? \ b| \ | _ _ _______face a / / /face / (...) The merging is done only for strict coplanar and adjacent facets, and the removed (...) (27 years ago, 15-Feb-00, to lugnet.cad.dev)
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Message is in Reply To:
| | Re: stl2dat conversion tool beta2
|
| (...) The normal is explicitely given in STL files. (...) Yes. I have planed to optimize this point. I think it is the same case for internal cylinders. The angle must be convex and not concav. However, it is not done yet. (...) I use case 1: _ _ (...) (27 years ago, 14-Feb-00, to lugnet.cad.dev)
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