Surface to surface tangency

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freecad-heini-1
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Re: Surface to surface tangency

Postby freecad-heini-1 » Sun Jun 07, 2020 2:46 pm

Pauvres_honteux wrote:
Sun Jun 07, 2020 1:15 pm
So what you, freecad-heini-1, is suggesting is there is one, and one only, who works on surface to surface tangency, i.e. Thomas "microelly2" ?
Thomas (microelly2) has a suitable tool in his Nurbs Workbench. But you have to convert the surfaces and edges or curves. This is a big disadvantage. Furthermore the tools are unfortunately not documented.

Some time ago I asked Werner a similar question, see:
https://forum.freecadweb.org/viewtopic. ... 17#p202217

As an online translator I use:
https://www.deepl.com/en/translator
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Pauvres_honteux
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Re: Surface to surface tangency

Postby Pauvres_honteux » Mon Jun 08, 2020 6:54 am

microelly2 wrote:
Tue Jan 28, 2020 5:38 pm
Hi Thomas, this question seems to boil down to: will you integrate your work on "surface to surface tangency" in master or not?
And do you want help with anything in this respect?
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Pauvres_honteux
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Re: Surface to surface tangency

Postby Pauvres_honteux » Tue Sep 15, 2020 1:49 pm

microelly2 seams to need a healthy break, hence no work from his side for a while.
.
vanuan wrote:
vanuan, you seam to have a lot of programming knowledge! Perhaps you could step forward and fix this show stopper once and for all?
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vanuan
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Re: Surface to surface tangency

Postby vanuan » Tue Sep 15, 2020 3:21 pm

Pauvres_honteux wrote:
Tue Sep 15, 2020 1:49 pm
vanuan, you seam to have a lot of programming knowledge! Perhaps you could step forward and fix this show stopper once and for all?
It looks like this is not so much a programming problem, but a calculus one. Unfortunately, I'm not proficient in calculus.

If you can provide the required formulas and describe the requirements in layman terms, I might look into it.

Currently, I don't have a slightest idea what is surface tangency and what is the workflow from the user perspective.
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vanuan
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Re: Surface to surface tangency

Postby vanuan » Tue Sep 15, 2020 3:35 pm

Did a bit of research.

It's pretty clear what the tangent line is:

https://en.wikipedia.org/wiki/Tangent

So you have a curve which is produced by some function. You choose a point on the curve. And you draw a line tangent to it.

To calculate that line position you get the derivative of the curve function.

By extrapolating 2D curve to 3D surface you can get the idea of what the tangent plane is. And there are formulas to calculate that plane in a specified point of the surface.

Now the term "surface to surface tangency". I don't get it. Is it a plane that is tangent to both surfaces? Does it mean surfaces need to intersect? Is it a curve that is a result of 2 surfaces intersecting? Or is it just a point where two surfaces touch?

Is there a picture that describes what you want?
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GlouGlou
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Re: Surface to surface tangency

Postby GlouGlou » Tue Sep 15, 2020 7:09 pm

and by re-sampling several faces I mean discretize the surfaces with n(U) an n(V)?
freecad-heini-1
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Re: Surface to surface tangency

Postby freecad-heini-1 » Wed Sep 16, 2020 5:24 am

vanuan wrote:
Tue Sep 15, 2020 3:35 pm
Is there a picture that describes what you want?
phpBB [video]

https://forum.freecadweb.org/viewtopic. ... 63#p272663
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vanuan
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Re: Surface to surface tangency

Postby vanuan » Wed Sep 16, 2020 5:48 am

freecad-heini-1 wrote:
Wed Sep 16, 2020 5:24 am
vanuan wrote:
Tue Sep 15, 2020 3:35 pm
Is there a picture that describes what you want?
https://forum.freecadweb.org/viewtopic. ... 63#p272663
Ok. So it seems to be implemented already?

It looks like you want to "blend" two surfaces by selecting their edges and creating another surface from these edges. So that you have 3 surfaces 1 of which depends on two others.

Am I describing it correctly?
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vanuan
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Re: Surface to surface tangency

Postby vanuan » Wed Sep 16, 2020 5:58 am

This seems to be supported by Open Cascade:

https://dev.opencascade.org/doc/refman/ ... ction.html

The question is how it should be modeled in FreeCAD: should it be a new object representing the blend, a new "blend" operation or a simple surface which isn't recomputed when two other surfaces change.

Which workbench should it be? Appears to be applicable to the Surface workbench?
chrisb
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Re: Surface to surface tangency

Postby chrisb » Wed Sep 16, 2020 6:22 am

Some informations for the non german speakers about the video linked by freecad-heini-1:

1:24 Explanations what could have happened if ...
2:04 Check what has been created
2:24 The blue lines are tangential at both ends
2:40 It's important to have on both sides the same number of segments
3:00 Explanations how the red and green faces were created by bezier curves