CGAL users discussion list

[Sylvain Pion <>]

Joshua A Levine a écrit :
> Hi CGALers,
>
> I was wondering about the mechanism for storing hidden vertices in the 
> Regular_Triangulation_3 class.  It seems that unlike in the 2D case, 
> these vertices are only stored as a list of weighted points associated 
> with whichever cell they are contained in.  There seems to be no global 
> way to access all of the hidden points for the triangulation (outside of 
> checking every cell).  Is this correct?
>
> Moreover, because they are stored as a list of weighted points instead 
> of as a list of actual vertices, it doesn't seem like there is a 
> mechanism for storing additional information associated with these 
> vertices.  By this I mean if I have a custom Vertex class with some 
> additional members, and if I'd like to use that class to store 
> additional information for a point I want to insert, I may not be able 
> to if that point becomes hidden.  Is there a recommended way to store 
> this sort of information without using some external bookkeeping?  Is 
> there even a moderately easy way to do it _with_ external bookkeeping?

What you can do is to setup a traits class with a different point type
which stores the information you need.  Then write the predicates
accordingly.  A quick hack might be to derive from the kernel point
type directly, then, nothing has to be done for predicates.  Harder
if you use constructions (e.g. circumcenters).

template <typename K>
struct My_traits
  : public K
{

  struct Point_3
    : typename K::Point_3 {

    // eventually repeate ctors.

    int my_id;
  };

};

Then :

typedef CGAL::...kernel...  K;
typedef My_traits<K>  Traits;
typedef CGAL::Delaunay..._3<Traits>  Delaunay;

...

> To keep it simple for discussion purposes, consider a 
> Regular_Triangulation_3 class where I want to store an associated id for 
> each vertex I insert.  But the triangulation is changing with both 
> insertions and deletions, so at any time a point I insert could itself 
> be hidden, or could hide other vertices already present.  Similarly, on 
> deletion I could unhide some points, but I'm pretty sure never hide 
> anything.


--
Sylvain Pion
INRIA Sophia-Antipolis
Geometrica Project-Team
CGAL, http://cgal.org/

Attachment: smime.p7s
Description: S/MIME Cryptographic Signature