他们之间的关系为：
Surface_mesh is a data structure that can be used as halfedge data structure or polyhedral surface. It is an alternative to the classes HalfedgeDS and Polyhedron_3 defined in the packages Halfedge Data Structures and 3D Polyhedral Surface.
The main difference is that Surface_mesh is indexed based and not pointer based, and that the mechanism for adding information to vertices, halfedges, edges, and faces is much simpler and done at runtime and not at compile time. When elements are removed, they are only marked as removed, and a garbage collection function must be called to really remove them.