Check if Polygon is flat on a Plane



  • On 28/06/2018 at 14:14, xxxxxxxx wrote:

    I want to check if a Polygon is flat and 100% on a Plane that is defined by another Objects XY-Axis.
    How can I do that? I am stuck here.



  • On 28/06/2018 at 23:01, xxxxxxxx wrote:

    Not sure if this is the most technically and/or mathematically correct solution, but I would check each polygon's vertex normal (=cross product of the vertex with next and previous vertex). If all normals are equal then I would assume the polygon to be flat.
    Additionally, when all these normals are equal to the Z axis (= cross product of X and Y axis) of your reference object, then I would assume the polygon AND flat AND 100% on the XY plane of that object.



  • On 29/06/2018 at 03:24, xxxxxxxx wrote:

    Hi Holgar, thanks for writing us.

    With regard to your question, and following C4DS hints, I recommend, given the four points arranged in such a fashion:
    A---B
    | \   |
    |  \  |
    D---C
    and that to run the following steps:

    1. check that the dot product between vectorAB and vectorZ is 0
    2. check that the dot product between vectorBC and vectorZ is 0
    3. check that the dot product between vectorAD and vectorZ is 0
    4. check that the Z-value of point A matches the Z-value of your XY-aligned plane

    Hope these few hints can help you to sort it out.

    Cheers, Riccardo


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