[solved] Cut two polygons in 2D

[reox]

I have this small example:

Code: Select all

import Part
i_wire = Part.makePolygon([
    App.Vector(0.2, 0.5, 0),
    App.Vector(0.5, 1.2, 0),
    App.Vector(1.2, 1.1, 0),
    App.Vector(0.8, 0.5, 0),
    App.Vector(0.2, 0.5, 0),
])
o_wire = Part.makePolygon([
    App.Vector(0,0,0),
    App.Vector(0,1,0),
    App.Vector(1,1,0),
    App.Vector(1,0,0),
    App.Vector(0,0,0),
])

Part.show(i_wire.cut(o_wire)))

I would like to get the following polygon afterwards:
[(0.2, 0.5, 0.0), (0.41428571428571426, 1.0, 0.0), (1.0, 1.0, 0.0), (1.0, 0.8, 0.0), (0.5, 1.2, 0.0)]

However, I get this polygon instead:
[(0.2, 0.5, 0.0), (0.41428571428571426, 1.0, 0.0), (0.8, 0.5, 0.0), (1.0, 0.8, 0.0), (1.2, 1.1, 0.0), (0.5, 1.2, 0.0)]
Which is the inner one including the two intersection points.

Is it possible to get the cut from these two polygons?
The only requirements I have are:
* 2D only
* I have the vertices of the two polygons
* I want the vertices of the output polygon

[mario52]

hi

Find intersection of a line with a Part2DObject

Code: Select all

s = FreeCADGui.Selection.getSelection()
sect = s[0].Shape.section(s[1].Shape)
points = sect.Vertexes
for i in points:
    print(i.Point)

other How to intersect a line with a part

Intersection between two Draft objects

Code: Select all

DraftGeomUtils.findIntersection(line1.Shape,line2.Shape)

mario

[reox]

But these only give me the intersection points:

Code: Select all

>>> print([(x.X, x.Y) for x in  i_wire.section(o_wire).Vertexes])
[(0.41428571428571426, 1.0), (1.0, 0.8)]

I would like to have the full polygon. I sketeched that really quick; I want to get the hatched polygon, i.e. the 5 vertices forming it:

20200222_150251_sw.png (82 KiB) Viewed 524 times

[wandererfan]

I would like to have the full polygon. I sketeched that really quick; I want to get the hatched polygon, i.e. the 5 vertices forming it:

How about:
Polygons -> Faces, Common(Face1, Face2), Common->OuterWire, OuterWire->Vertexes, Vertexes->Polygon.

Might not need the OuterWire steps.

[reox]

Polygons -> Faces, Common(Face1, Face2), Common->OuterWire, OuterWire->Vertexes, Vertexes->Polygon.

Yes! That works!

Code: Select all

import Part

inner = [
    App.Vector(0.2, 0.5, 0),
    App.Vector(0.5, 1.2, 0),
    App.Vector(1.2, 1.1, 0),
    App.Vector(0.8, 0.5, 0),
    App.Vector(0.2, 0.5, 0),
]

outer = [
    App.Vector(0,0,0),
    App.Vector(0,1,0),
    App.Vector(1,1,0),
    App.Vector(1,0,0),
    App.Vector(0,0,0),
]

i_wire = Part.makeFace(Part.makePolygon(inner), 'Part::FaceMakerSimple')
o_wire = Part.makeFace(Part.makePolygon(outer), 'Part::FaceMakerSimple')

section = i_wire.common(o_wire)
assert len(section.Wires) == 1, 'there are none or multiple wires!'

print([(x.X, x.Y) for x in section.Wires[0].OrderedVertexes])

gives:
[(0.8, 0.5), (0.2, 0.5), (0.41428571428571426, 1.0), (1.0, 1.0), (1.0, 0.8)]

Thanks a lot!

[vocx]

Yes! That works!

This seems to be the same as using the Part_Common tool. Although it seems to be intended for 3D objects it also works for 2D objects. It should work, I think, for every object that has a Part_TopoShape, so essentially all geometrical objects created in FreeCAD.

[reox]

Yes! That works!

This seems to be the same as using the Part_Common tool. Although it seems to be intended for 3D objects it also works for 2D objects. It should work, I think, for every object that has a Part_TopoShape, so essentially all geometrical objects created in FreeCAD.

I tried Part.Wire.common() before (which I also thought would be the operation I needed), but it returned an empty shape instead.

[vocx]

...
I tried Part.Wire.common() before (which I also thought would be the operation I needed), but it returned an empty shape instead.

Use Part_Common and see the generated code. It creates a third object, which uses the two other objects internally.