:returns: shapely.Polygon object of the z=0 projection of 
            this polygon.

def get_shapely(self):
        """
        :returns: shapely.Polygon object of the z=0 projection of 
            this polygon.
        """
        if self.shapely == None:
            from shapely.geometry import Polygon as shPolygon
            self.shapely = shPolygon(self.points[:, :2]) # z=0 projection!
        return self.shapely