CGAL users discussion list

["Wang Weiwei" <>]

You can use your own observer (derived from
CGAL::Arr_observer<Arrangement_2>). Look at face_extension.cpp to see
how it's done for faces.

Hello Fogel,

Thanks very much for your hints.

Yes, I found the example in ex_face_extension.C. But my needs seems not to be 
fully met. To declare a class derived from CGAL::Arr_observer<Arrangement_2>, 
and then override the before_create_vertex() method, I can capture the event 
of the insertion of a new vertex. But still one problem is that there's only a
Arr_face_extended_dcel type in CGAL, no Arr_vertex_extended_dcel available. I 
cannot associate data with the vertices as this way. The other problem is 
that 
the way I'm constructing the arrangement is like this:

    typedef CGAL::Exact_predicates_inexact_constructions_kernel  Kernel;
    typedef CGAL::Arr_segment_traits_2<Kernel>                          
Traits_2;
    typedef Traits_2::Point_2                                                 
          Point_2;
    typedef Traits_2::X_monotone_curve_2                                      
  Segment_2;
    typedef CGAL::Arr_extended_dcel<Traits_2, int, int, int>Dcel;
    typedef CGAL::Arrangement_2<Traits_2, Dcel>                         
Arrangement_2;

    struct Point_2_with_id
    {
            int id;
            float x, y;
    };

    std::vector<Point_2_with_id> points;
        std::list<Segment_2> segments;

        for(std::vector<Point_2_with_id>::const_iterator it=points.begin(); 
it != points.end(); ++it)
        {
                segments.push_back ( 
                        Segment_2 ( Point_2( it->x, it->y ), Point_2( /*some 
other point*/ ) ) 
                                        );
    }

The user data (here means the id of a point) was discarded during cunstructing
a segment.

I think it would be better if I can derive a class from Point_2, and if I 
can build the arrangement with the derive points.

Thanks again.

Max


Wang Weiwei wrote:

>Hi all,
>
>I'm using the Arrangement_2 module of CGAL.
>
>I want to attach some user information to the vertices of the arrangement. 
>I've found some example code in the example folder of the CGAL lib (such as
>ex_dcel_extension.C). 
>
>Unfortunately, in this example, the user data are attached to the vertices, 
>halfedges and faces after the arrangement was built. What I want to know is 
>how I can attach these user data to the vertices during the construction of 
>the arrangement. For those vertices newly created during the intersection of 
>the curves, a pre-specified default value will be ok.
>
>Thanks in advance for any help.
>
>Sorry for the previous message with the subject not correct.
>
>Max
>  
>
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