[geometry] How to get the intersection face from two overlaping ConvexPolygon3D instances?

[Bai Song]

Hi, Geometry Team


I'm learning this interesting project and facing some difficulties when i did a 
little experiment.


I created two ConvexPolygon3D instances (2 white rectangles in below image) on 
the same plane, and try to get the overlaping area(blue part) by 
RegionBSPTree3D intersection operation.




But i got null when getting the centroid of the intersection. It looks that 
this test of intersection failed.

Could you tell me how can i fix this?



Thanks for your contribution to this project!


//---------my test codes----------

public class TestIntersection
{
    public static void main(String args[])
    {
        Precision.DoubleEquivalence precision = 
Precision.doubleEquivalenceOfEpsilon(1e-6);

        List<Vector3D> pts1 = new ArrayList<>();
        pts1.add(Vector3D.of(0, 10, 0));
        pts1.add(Vector3D.of(30, 10, 0));
        pts1.add(Vector3D.of(30, 20, 0));
        pts1.add(Vector3D.of(0, 20, 0));
        ConvexPolygon3D face1=Planes.convexPolygonFromVertices(pts1, precision);

        List<Vector3D> pts2 = new ArrayList<>();
        pts2.add(Vector3D.of(10, 0, 0));
        pts2.add(Vector3D.of(20, 0, 0));
        pts2.add(Vector3D.of(20, 30, 0));
        pts2.add(Vector3D.of(10, 30, 0));
        ConvexPolygon3D face2 = Planes.convexPolygonFromVertices(pts2, 
precision);

        List<ConvexPolygon3D> list1 = new ArrayList<>();
        list1.add(face1);
        RegionBSPTree3D bsp1 = RegionBSPTree3D.from(list1);

        List<ConvexPolygon3D> list2 = new ArrayList<>();
        list2.add(face2);
        RegionBSPTree3D bsp2 = RegionBSPTree3D.from(list2);

        RegionBSPTree3D result = RegionBSPTree3D.empty();
        result.intersection(bsp1, bsp2);

        System.out.println("Hello, Geometry! Centroid: "+result.getCentroid()); 
//expect (15,15,0), but got null actually
    }
}