@classmethod
def get_shapedef(cls, name, params):
    """Get a previously-registered shape of any type by its name"""
    if name in cls.convex_polyhedron_functions:
        return cls.convex_polyhedron_shapedef(name, params)
    elif name in cls.polygon_functions:
        return cls.polygon_shapedef(name, params)
    else:
        raise NotImplementedError()
