CGAL users discussion list

[Ben Supnik <>]

Have you edited the "contained" flags at all?  A face is either 
contained or not contained in a general polygon set built off of an 
arrangement.  (The contained property becomes part of faces due to the 
use of the GPS traits bases...)

Anyway, if you don't (1) set contained how you want it and (2) remove 
redundant edges (edges where faces on either side are both contained, or 
edges that have the same face on both sides) I think you will not get 
correct results.

When working ONLY with the polygon ops code, this is done for you, but 
if you want to put a bunch of segments in yourself, you must do this!

I do this by doing a traversal of the face from the outside in, toggling 
containment each time I cross a halfedge.  This gives me a "toggling" 
property.  My code is here but it might be too muddled to be useful.

http://dev.x-plane.com/cgit/cgit.cgi/xptools.git/tree/src/XESCore/MapTopology.h
http://dev.x-plane.com/cgit/cgit.cgi/xptools.git/tree/src/XESCore/MapTopology.cpp

There may also be better CGAL utils to do what I am doing...I wrote that 
code a while ago.

cheers
ben


Jo wrote:
> Ben Supnik's first hint using the "Arr_bfs_scanner" class.
> I'm not sure the result. 1 polygon to have 3 holes.
>
> #include <CGAL/Gmpq.h>
> #include <CGAL/Lazy_exact_nt.h>
> #include <CGAL/Cartesian.h>
> #include <CGAL/Arrangement_2.h>
> #include <CGAL/Boolean_set_operations_2/Gps_default_dcel.h>
> #include <CGAL/Gps_segment_traits_2.h>
> #include <CGAL/General_polygon_set_2.h>
> #include <CGAL/General_polygon_with_holes_2.h>
> #include <list>
>
> typedef CGAL::Gmpq						       
> Number_type;
> typedef CGAL::Lazy_exact_nt<Number_type>			       
> Lazy_exact_nt;
> typedef CGAL::Cartesian<Lazy_exact_nt>                                    
> Kernel;
> typedef Kernel::Point_2 					       
> Point_2;
> typedef Kernel::Segment_2					       
> Segment_2;
> typedef CGAL::Gps_segment_traits_2<Kernel>			       
> Traits_2;
> typedef CGAL::Gps_default_dcel<Traits_2>                          Dcel;
> typedef CGAL::Arrangement_2<Traits_2, Dcel>			       
> Arrangement2;
> typedef CGAL::General_polygon_set_2<Traits_2>			       
> Polygon_set_2;
> typedef Traits_2::General_polygon_with_holes_2			       
> Polygon_with_holes_2;
> typedef std::back_insert_iterator<std::list<Polygon_with_holes_2> >    
> OutputIterator;
> typedef CGAL::Arr_bfs_scanner<Arrangement2, OutputIterator>	       
> Arr_bfs_scanner;
>
> int main()
> {
>     Arrangement2 arr;
>     std::list<Segment_2> segments;
>
>     segments.push_back(Segment_2(Point_2(0,0), Point_2(50,0)));
>     segments.push_back(Segment_2(Point_2(50,0), Point_2(50,30)));
>     segments.push_back(Segment_2(Point_2(50,30), Point_2(30,30)));
>     segments.push_back(Segment_2(Point_2(30,30), Point_2(30,10)));
>     segments.push_back(Segment_2(Point_2(30,10), Point_2(10,10)));
>     segments.push_back(Segment_2(Point_2(10,10), Point_2(10,40)));
>     segments.push_back(Segment_2(Point_2(10,40), Point_2(20,40)));
>     segments.push_back(Segment_2(Point_2(20,40), Point_2(20,20)));
>     segments.push_back(Segment_2(Point_2(20,20), Point_2(40,20)));
>     segments.push_back(Segment_2(Point_2(40,20), Point_2(40,50)));
>     segments.push_back(Segment_2(Point_2(40,50), Point_2(0,50)));
>     segments.push_back(Segment_2(Point_2(0,50), Point_2(0,0)));
>
>     insert(arr, segments.begin(), segments.end());
>
>     Polygon_set_2 s;
>     std::list<Polygon_with_holes_2> res;
>     OutputIterator out = std::back_inserter(res);
>
>     Traits_2 trait;
>     Arr_bfs_scanner scanner(&trait, out);
>     scanner.scan(arr);
>     
>     std::cout<<std::endl;
>     std::cout<<"Number of polygon : "<<res.size()<<std::endl;
>     std::list<Polygon_with_holes_2>::const_iterator it;
>     int i=1;
>     for (it=res.begin(); it!=res.end(); ++it, ++i)
>         std::cout<<"#"<<i<<" Number of holes :
> "<<it->number_of_holes()<<std::endl;
>
>     return 0;
> }
>
> I hope that somebody draw the shapes on a screen to confirm the result.
> Thans.

--
Scenery Home Page: http://scenery.x-plane.com/
Scenery blog: http://xplanescenery.blogspot.com/
Plugin SDK: http://www.xsquawkbox.net/xpsdk/
X-Plane Wiki: http://wiki.x-plane.com/
Scenery mailing list: 

Developer mailing list: