Re: [geometry] Transition from PolyhedronSet to ??? (RegionBSPTree3D ?)

[Matt Juntunen]

Hi Sven,

If the createVertices and createFacets methods don't construct convex polygons 
then perhaps you could bypass them completely and just construct the tree 
directly from the boundaries. Assuming that I understand your use case 
correctly, the following methods should do what you want:

private RegionBSPTree3D createPrism(List<Vector2D> polygon,
        double upperBound, double lowerBound,
        DoublePrecisionContext precision) {

    EmbeddingPlane plane = Planes.fromPointAndPlaneVectors(Vector3D.of(0, 0, 
lowerBound),
            Vector3D.Unit.PLUS_X, Vector3D.Unit.PLUS_Y, precision);

    Vector3D extrudeVector = plane.getNormal().withNorm(upperBound - 
lowerBound);

    return extrudePolygon(polygon, plane, extrudeVector, precision);
}

private RegionBSPTree3D extrudePolygon(List<Vector2D> polygon, EmbeddingPlane 
plane,
        Vector3D extrudeVector, DoublePrecisionContext precision) {

    List<Vector3D> basePoints = plane.toSpace(polygon);
    List<Vector3D> extrudedPoints = basePoints.stream()
            .map(extrudeVector::add)
            .collect(Collectors.toList());

    RegionBSPTree3D tree = RegionBSPTree3D.empty();

    // treat the plane as the top and the extruded plane as the bottom;
    // we'll invert the tree at the end if needed
    tree.insert(plane.span()); // top
    tree.insert(Planes.fromPointAndNormal(
            plane.getOrigin().add(extrudeVector),
            plane.getNormal().negate(),
            precision).span()); // bottom

    // create the sides of the prism
    int size = polygon.size();
    for (int i = 0; i < size; ++i) {
        tree.insert(Planes.convexPolygonFromVertices(Arrays.asList(
                    basePoints.get(i),
                    extrudedPoints.get(i),
                    extrudedPoints.get((i + 1) % size),
                    basePoints.get((i + 1) % size)
                ), precision));
    }

    // complement the tree if the "top" wasn't actually the top
    if (plane.getNormal().dot(extrudeVector) > 0) {
        tree.complement();
    }

    return tree;
}

Note that these methods assume that the polygon contains at least 3 unique 
vertices, the first vertex is not repeated at the end, and that the upper and 
lower bounds are not equal.

Hopefully this helps.

Regards,
Matt

________________________________
From: Sven Rathgeber <sven.rathge...@web.de>
Sent: Tuesday, June 16, 2020 3:46 AM
To: Commons Developers List <dev@commons.apache.org>
Subject: Re: [geometry] Transition from PolyhedronSet to ??? (RegionBSPTree3D ?)

Hi Matt,

 > 2. Yes, the LinecastPoint3D object that you get from linecasting
contains the intersection point as well as the surface normal at the
point of intersection.

thanks - that did the job and I could do the whole refactoring, but the
tests fail.

We used the PolyHedronsSet to model non-convex regions and that worked well.

Now the "indexedConvexPolygons" is strict and forbids that (walk your
talk :) ).

Is there a way to handle non-convex regions ?

Regards,

Sven



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