Geotools creating polyhedral surfaces from polygons

Question

I have polygon geometries that represent building footprints in a shapefile and I want to extrude them according to an attribute "height" and turn them 3B objects as polyhedral surfaces via extrusion. For this purpose I am writing an extrusion function. I am using geotools to access and extract geometries and attributes from shapefile. I am creating top and bottom faces of buildings as polygon geometries but I could not generate vertical faces. I could not write a loop that traverse positions and create vertical faces as polygon geometries. I am stuck with it.

Here is the rest of my code after I extract polygons ;

List<Polygon> polygons = bb.getBboxFeature(shapeFilePath);

List<PolyhedralSurface> mesh = new ArrayList<PolyhedralSurface>();

for(Polygon poly : polygons) {

    Coordinate[] coords = poly.getCoordinates();
    List<Polygon> faces = new ArrayList<Polygon>();

    for (int i =0; i<coords.length; i++) {

        Double h = 15.00;
        GeometryBuilder builder = new GeometryBuilder(DefaultGeographicCRS.WGS84_3D);
        List<Position> dpsBottom = new ArrayList<Position>();
        List<Position> dpsTop = new ArrayList<Position>();

        //bottom positions created using coordinates

        dpsBottom.add(builder.createDirectPosition(new double[] {coords[i].x, coords[i].y, 0}));

        //top positions created using coordinates

        dpsTop.add(builder.createDirectPosition(new double[] {coords[i].x, coords[i].y, h}));

My final purpose is create vertical faces and add them to a polygon list. Then, finaly giving this list to createPolyhedralSurface() function as input and create building as polyhedral geometry.

Is there a more efficient solution for my purpose?

Answer 1

In principal, this code should do what you want:

public PolyhedralSurface extrudePolygon(Polygon poly, double h) {
    Coordinate[] polyPoints = poly.getBoundary().getCoordinates();
    List<org.opengis.geometry.coordinate.Polygon> faces = new ArrayList<>();

    for (int i = 1; i < poly.getNumPoints(); i++) {
      double[] coords = new double[15];
      coords[0] = polyPoints[i - 1].x;
      coords[1] = polyPoints[i - 1].y;
      coords[2] = 0;
      coords[3] = polyPoints[i].x;
      coords[4] = polyPoints[i].y;
      coords[5] = 0;
      coords[6] = polyPoints[i].x;
      coords[7] = polyPoints[i].y;
      coords[8] = h;
      coords[9] = polyPoints[i - 1].x;
      coords[10] = polyPoints[i - 1].y;
      coords[11] = h;
      coords[12] = polyPoints[i - 1].x;
      coords[13] = polyPoints[i - 1].y;
      coords[14] = 0;
      PointArray points = builder.createPointArray(coords);
      // for each edge create a polygon
      SurfaceBoundary surfaceBoundary = builder.createSurfaceBoundary(points);
      org.opengis.geometry.coordinate.Polygon face = builder.createPolygon(surfaceBoundary);
      faces.add(face);
    }
    faces.add(poly);
    //add top face too
    return builder.createPolyhedralSurface(faces);
  }

But, this fails because the Geometry validation code seems to only work in two dimensions so it thinks the face polygons intersect. You can skip this test by adding:

hints.put(Hints.GEOMETRY_VALIDATE, false);

But then you get to the real problem, org.geotools.geometry.iso.coordinate.GeometryFactoryImpl.createPolyhedralSurface is not implemented (yet).