CGAL users discussion list

["Wang Weiwei" <>]

Thanks again for your help, Fogel.
In fact, I have finished my program in a way that I think is fairly ugly.
I'm just finding an elegant way to do the same thing.

B/Rgds
Max

>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 
>  
>
Read the Arrangement_2 manual. You can extend the Vertex, Halfedge, and
Face types in a similar way. Also, there is Arr_extended_dcel.h, which
you may find convenient.

>cannot associate data with the vertices as this way. The other problem is 
>that 
>the way I'm constructing the arrangement is like this:
>  
>
Regarding this problem if I understand it right, you have at least two
options. You can create a map that maps points to data. When a vertex is
created, find the data of the corresponding point, and store it in the
vertex. Or, you can derive a new Kernel::Point_2. This requires some
knowledge, which you will have to look for at the Kernel manual (Look
for Extensible Kernel).


>    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
>> 
>>
>>    
>>

-- 
   ____  _        ____             _
  /_____/_) o    /__________  __  //
 (____ (   (    (    (_/ (_/-(-'_(/
                         _/




-- 
You are currently subscribed to cgal-discuss.
To unsubscribe or access the archives, go to
https://lists-sop.inria.fr/wws/info/cgal-discuss