Determining geometry as concave or convex

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microelly2
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Re: Determining geometry as concave or convex

Post by microelly2 »

You are right, we have to discover the complete surface, but this can be done fast.
For meshes there is a curvature plot method in the mesh wb.
here is an example calculated for a 42000 points mesh in less than 1 s
bp_770.png
bp_770.png (261.63 KiB) Viewed 619 times
the blue areas indicate where local concavety starts
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JoshM
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Re: Determining geometry as concave or convex

Post by JoshM »

That's so cool! Is that a tool you've made available? My boss was asked me a week ago if FreeCAD could be used to color map a topological surface.

A lot of machining can be done with precision of 0.01 mm. Backlash and other machine limits waste greater precision.

Thanks so much for your help.
-Josh
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microelly2
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Re: Determining geometry as concave or convex

Post by microelly2 »

JoshM wrote: Tue Apr 24, 2018 11:07 pm That's so cool! Is that a tool you've made available? My boss was asked me a week ago if FreeCAD could be used to color map a topological surface.
the last picture is from the core mesh workbench,
but there are othe visualization tools too - for example look into the FEM area.

I played with different modes - add a color map to a surface or draw colored vector fields.
examples see here
https://forum.freecadweb.org/viewtopic. ... 70#p211441

the main task is to get the data from the surface.
sariug
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Re: Determining geometry as concave or convex

Post by sariug »

Hello.

Firstly sorry for resurrecting such an old topic.

The mesh curvature is nice for having general ideas. But mesh curvature is not always so accurate.

On the other hand, when these variables are taken from the surface information (curvatureAt ect) the curvature between meshes is lost(Thats the advantage of mesh curvature.)

Lets get to the real question. How to determine the curvature sign, according to convexity and concavity ?

Check the file in attachment. About the three colored axes :
- Black : surface normal
- Blue : Surface curvature tangent U
- Red : Surface curvature tangent V

The right side of the face has definitely a concavity,
The left side on the other hand convex.

The question is how to determine these signs for curvatures. It seems totally random(Value is correct)
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