point on face of solid

[Torxal]

Hey everybody,

for a given FreeCAD.Vector i want to check if there is a face of a solid object nearby.

For example i create a box with the default edge length of 10 mm with:

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App.ActiveDocument.addObject("Part::Box","Box")

TheBox.PNG (8.19 KiB) Viewed 789 times

Now i can create a Vector with:

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poi = FreeCAD.Vector(5,10,5) 

From using the GUI i know that poi should be on face4. So i get face 4 with:

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foi = App.ActiveDocument.Box.Shape.Faces[4]

TheBox2.PNG (12.69 KiB) Viewed 783 times

Now i want to check if poi is nearby/inside with tolerance foi.

So i call:

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 foi.isInside(poi,2.5,True)

The result is for every tolerance i set is:

False:

What can i do? I found this unsolved old post https://forum.freecadweb.org/viewtopic. ... =3&t=31524 with a similar problem.

Using:
FreeCAD 0.19
Windows 10

[TheMarkster]

Faces[4] is not Face4, it's Face5 since Faces is 0-indexed.

[Torxal]

@TheMarkster thanks ! My fault . So i call face 5. But why i dont get a True for a big tolerance like 1000?

[Chris_G]

Function isInside splits shapes in 2 groups :
- volumetric shapes are treated with BRepClass3d_SolidClassifier
- non-volumetric shapes are treated with BRepExtrema_DistShapeShape

I think there is a bug here, and Faces should be treated as non-volumetric, along with vertexes, edges and wires.

[onekk]

I think there is a bug here, and Faces should be treated as non-volumetric, along with vertexes, edges and wires.

Maybe asking @wmayer could be a good idea?

From OCC documentation you linked about BRepExtrema_DistShapeShape:

This class provides tools to compute minimum distance between two Shapes (Compound,CompSolid, Solid, Shell, Face, Wire, Edge, Vertex).

So it could be used on these entities, but maybe there are or there were some problems with the class in some corner cases, and sadly if there are no comments, in the source code it is difficult to say something.

But as "wmayer committed on 23 Oct 2021" :

https://github.com/FreeCAD/FreeCAD/comm ... 2645605c13


It will be interesting to see what he has to say about this choice, at least to improve knowledge if internals, I'm saving most of the latest wmayer posts, as they are very interesting and almost always improve my personal knowledge about FC.

Sorry for bothering and not giving relevant information about the OT.

Regards

Carlo D.

[wmayer]

Yes, it's a bug and is fixed with git commit 639ff927de.

[wmayer]

I think an even better option is the class BRepClass_FaceClassifier because similar to BRepClass3d_SolidClassifier you can distinguish between a point is part of the inner of a face or on its boundary.

EDIT: No, it's not. It unexpectedly returns true for

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box.Face4.isInside(FreeCAD.Vector(5,11,5), 0.0, False)

or

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box.Face4.isInside(FreeCAD.Vector(5,9,5), 0.0, False)