CGAL users discussion list

[Mael <>]

Hello,

With CGAL, you can pass any policy you want as long as it fits some requirements. The requirements on a placement class is very light and is defined there: https://doc.cgal.org/5.0/Surface_mesh_simplification/classGetPlacement.html. thus, your class  must provide the functor:

    boost::optional< Point > operator() (Profile const &edge_profile) const

The "edge profile" is a class that regroups all information useful during the collapse of an edge. Its interface is described there: https://doc.cgal.org/5.0/Surface_mesh_simplification/classEdgeProfile.html. In particular, you see that you can obtain the edge being collapse via v0_v1 (or v1_v0, since these are halfedges). You can use the function is_border_edge (https://doc.cgal.org/5.0/BGL/group__PkgBGLHelperFct.html#ga63695419c5ce7f68949ff2fb4f42d733) to know if your edge is on the border (check out https://doc.cgal.org/5.0/BGL/index.html for details on the graph API).

You can then simply derive a new policy from Lindstrom-Turk and do something like:

struct my_custom_placement
   : public lindstorm-turk placement
{
    boost::optional< Point > operator() (Profile const &edge_profile) const
   {
      if(is_border_edge(edge_profile.v0_v1()))
        return whichever extremity point you want;
      else
        return base::operator()(edge_profile);
   }  

};

Best,
Mael

    On 13/10/2019 01:46, tdchen wrote:
    
I'm a newbie both to STL and CGAL.
I found that the CGAL surface_mash_simplification might be very helpful to
my work.
But I have to change it a little to suit my needs.
Specifically, I want to change the placement policy to that: the border edge
will be collapsed to one of its vertices and others to the Lindstrom-Turk
position.
I wonder if it is convenient in CGAL.
It seems there is no such a placement policy in curent version of CGAL.
Thanx.



--
Sent from: http://cgal-discuss.949826.n4.nabble.com/