:returns: matplotlib Poly3DCollection
        :rtype: list of mpl_toolkits.mplot3d

def get_plotable3d(self):
        """
        :returns: matplotlib Poly3DCollection
        :rtype: list of mpl_toolkits.mplot3d
        """
        polyhedra = sum([polyhedron.get_plotable3d() 
                         for polyhedron in self.polyhedra], [])
        return polyhedra + self.surface.get_plotable3d()