CGAL users discussion list

[Markus Eich <>]

Dear all,

I am using CGAL in order the get one or more alpha polygons from a 
shape. IN a first approach I assume there are no holes. I generate the 
segements as follows:


    Alpha_shape_2 as(lp.begin(),lp.end());

    // find optimal alpha value

    Alpha_iterator opt = as.find_optimal_alpha(1);
    as.set_alpha((*opt)*2.0f);
    as.set_mode(Alpha_shape_2::REGULARIZED);

    std::vector<K::Segment_2> segments;
    std::vector<K::Segment_2> sorted_segments;

    for(Alpha_shape_edges_iterator it =  
as.alpha_shape_edges_begin();it != as.alpha_shape_edges_end(); ++it)
        segments.push_back(as.segment(*it));

    std::cout << segments.size() << " alpha shape edges" << std::endl;


This works fine an I get all the segments. My problem is that I need a 
single polygon (in my example I only have one concave shape). If I 
iterate over  the std::vector<K::Segment_2> segments vector, the 
segments are like E,A,V,D,C,F , instead of A,B,C,D,E,F. In need the 
segments in an ordered way i.e. that the  .target() of A is the 
.source() of B, the .target() of B the source of C, and so on.

How can I achieve this using CGAL? Is there a way to sort the segments 
directly?


Thank you and cheers,

Markus


--
Dipl. Inf. Markus Eich
Researcher

DFKI Bremen
Robotics Innovation Center
Mary-Somerville-Str. 9
28359 Bremen, Germany

Phone: +49 (0)421 17845-4105
Fax:   +49 (0)421 17845-4150
E-Mail: 


Weitere Informationen: http://www.dfki.de/robotik
-----------------------------------------------------------------------
Deutsches Forschungszentrum fuer Kuenstliche Intelligenz GmbH
Firmensitz: Trippstadter Straße 122, D-67663 Kaiserslautern
Geschaeftsfuehrung: Prof. Dr. Dr. h.c. mult. Wolfgang Wahlster
(Vorsitzender) Dr. Walter Olthoff
Vorsitzender des Aufsichtsrats: Prof. Dr. h.c. Hans A. Aukes
Amtsgericht Kaiserslautern, HRB 2313
Sitz der Gesellschaft: Kaiserslautern (HRB 2313)
USt-Id.Nr.:    DE 148646973
Steuernummer:  19/673/0060/3
-----------------------------------------------------------------------