Allplan Forum: Sorting Polyhedron Vertices After Modification

Doom235

20.03.2025 - 08:00

Hi, I would like to ask about the geometry of the Polyhedron object. When I select a polyhedron and use GetVertices(), I receive a list of points sorted in a counter-clockwise order. However, if I make a small modification, like using the CutPolyhedronWithPlane() function, the list returned by GetVertices() no longer follows the counter-clockwise order. This makes it difficult to sort the points correctly to get the actual geometry. Is there any way to always retrieve the list of points in counter-clockwise order or a method to sort the points correctly again?

Thank you!

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cmaignan_m…

21.03.2025 - 09:07

Hi,

You can try to reorder the new list based on the first one.

For example :

list_a = [Geometry.Point3D(243040,-423998,1000), Geometry.Point3D(243040,-423998,5000), Geometry.Point3D(243040,-421073,5000)]
list_b = [Geometry.Point3D(243040,-423998,2500), Geometry.Point3D(243040,-423998,1000), Geometry.Point3D(243040,-421073,2500), Geometry.Point3D(243040,-423998,5000), Geometry.Point3D(243040,-421073,5000)]

result = list_a.copy()

for index, value in enumerate(list_b):
    if value not in list_a:
        result.append(value)

Best
Christophe

bmarciniec

24.03.2025 - 09:29 * [Post più utile]

Quotato da: Doom235

Hi!

Is the original polyhedron a closed volume polyhedron? Is it negative? (polyhedron.IsNegative()). Is its volume positive when calculated using CalcMass?
I can imagine, that the original os not positive and the algorithm is trying to make it this way. That's why the discrepancy. Try to experiment with "Invert" and "InvertWithFlagUnchanged"

Best,
Bart