Intersection doesn't work.

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Intersection doesn't work.

Henry Baker
The following OpenSCAD program doesn't work.  It should produce a tetrahedron (not regular).

I set convexity to be larger than 1, but that doesn't seem to help.

// Testing OpenSCAD version 2013.06

intersection() {

multmatrix([[-1, 0, 0, 0], [0, -1, 0, 0], [0, 0, -1, 0], [0, 0, 0, 1]])
polyhedron(points = [[100, 0, 0], [-50, -86.6025, 0], [-50, 86.6025, 0]], triangles = [[0, 1, 2]], convexity = 5);

multmatrix([[1, 0, 0, 0], [0, 0, -1, 0], [0, 1, 0, 0], [0, 0, 0, 1]])
polyhedron(points = [[100, 0, 0], [-50, -86.6025, 0], [-50, 86.6025, 0]], triangles = [[0, 1, 2]], convexity = 5);

multmatrix([[0, 0, -1, 0], [0, 1, 0, 0], [1, 0, 0, 0], [0, 0, 0, 1]])
polyhedron(points = [[100, 0, 0], [-50, -86.6025, 0], [-50, 86.6025, 0]], triangles = [[0, 1, 2]], convexity = 5);

multmatrix([[0.788675, -0.211325, 0.57735, 10], [-0.211325, 0.788675, 0.57735, 10], [-0.57735, -0.57735, 0.57735, 10], [0, 0, 0, 1]])
polyhedron(points = [[100, 0, 0], [-50, -86.6025, 0], [-50, 86.6025, 0]], triangles = [[0, 1, 2]], convexity = 5);
}

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Re: Intersection doesn't work.

kintel
Administrator
On 2013-06-27, at 10:16 , Henry Baker wrote:

> The following OpenSCAD program doesn't work.  It should produce a tetrahedron (not regular).
>
You can only intersect solids, and your polyhedrons are planar.
You cannot use OpenSCAD to build a volume from intersecting planes.

You could build 2D polygons, linear_extrude them and rotate them in place, then do the intersection and you might get what you're looking for.

 -Marius

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Re: Intersection doesn't work.

Henry Baker
In reply to this post by Henry Baker
I'm trying to intersect 3 cubes, but for some reason, OpenSCAD seems to ignore the first cube in the following intersection.

The result should be a cube entirely in the 1st octant.

The intersection of cubes 2 & 3 works fine, but the intersection with cube 1 doesn't work.

// Test OpenSCAD version 2013.06

intersection() {

multmatrix([[-1, 0, 0, 0], [0, -1, 0, 0], [0, 0, -1, 0], [0, 0, 0, 1]])
multmatrix([[1, 0, 0, 0], [0, 1, 0, 0], [0, 0, 1, -50], [0, 0, 0, 1]])
cube(size = [100, 100, 100], center = true);

multmatrix([[1, 0, 0, 0], [0, 0, -1, 0], [0, 1, 0, 0], [0, 0, 0, 1]])
multmatrix([[1, 0, 0, 0], [0, 1, 0, 0], [0, 0, 1, -50], [0, 0, 0, 1]])
cube(size = [100, 100, 100], center = true);

multmatrix([[0, 0, -1, 0], [0, 1, 0, 0], [1, 0, 0, 0], [0, 0, 0, 1]])
multmatrix([[1, 0, 0, 0], [0, 1, 0, 0], [0, 0, 1, -50], [0, 0, 0, 1]])
cube(size = [100, 100, 100], center = true);
}

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Re: Intersection doesn't work.

kintel
Administrator
On 2013-06-27, at 11:36 , Henry Baker wrote:

> I'm trying to intersect 3 cubes, but for some reason, OpenSCAD seems to ignore the first cube in the following intersection.
>
> The result should be a cube entirely in the 1st octant.
>
> The intersection of cubes 2 & 3 works fine, but the intersection with cube 1 doesn't work.
>
Works in OpenCSG mode, but not ing CGAL mode - definitely looks like a bug..
Same behavior in all previous versions of OpenSCAD

 -Marius

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