CGAL users discussion list

Yes, as Ben pointed out, the computation is different. The function  
that you are using (S.intersection) applies a recursive procedure  
until the no. of polygons reduces below a certain threshold. Then,  it  
performs a sweep-line procedure. When you provide a polygon at a time,  
I think that the sweep-line procedure is immediately invoked. Anyhow,  
thanks for the info. We'll take it in account when we look into it.

Quoting "Ben Supnik" 
<>:

> Hi Hichem,
>
> The order of computation is different - the first (failing) case is  
> I think more efficient because the code can use a merge-sort-like  
> sequence.
>
> You say that your polygons "seem" to be correct...did you use the  
> CGAL tests for self-intersection, etc. or a different unrelated set  
> of code to check the input data?
>
> Also, I'm not sure what the MSVC version of -frounding-math is...if  
> the low level rounding in CGAL is incorrect, polygon ops can become  
> intermittently unreliable...I saw that when I had compiler options  
> wrong, and the symptoms were similar.
>
> cheers
> Ben
>
> BBB HHH wrote:
> > Hello,
> >
> > I tried to compute the intersection of the polygons by inserting  
> > each polygon apart like this:
> >
> > std::vector<Polygon_2>        polygons;
> > // Fill the list of polygons
> > Initialize the polygon set with a polygon
> > Polygon_set_2 S(first_polygon);
> > // Instead of S.intersection(polygons.begin(), polygons.end());
> > for (int i = 0; i != polygons.size(); ++i)
> > {
> >    S.intersection(polygons[i];
> > }
> >
> > This variation of source code is working fine for the polygons I  
> > attached to the previous e-mail. I do not know what is the  
> > difference (perhaps in runtime or storage) between the first source  
> > code (which didn't work) and the second one?
> >
> > Thanks
> > Hichem
> >
> > ------------------------------------------------------------------------
> > *De :* BBB HHH 
> > <>
> > *À :* 
> >
> > *Envoyé le :* Samedi, 26 Septembre 2009, 18h25mn 19s
> > *Objet :* Re : [cgal-discuss] An error when trying to compute  
> > intersection of polygons
> >
> > Hello,
> >
> > Attached to this e-mail, you can find the .dat files storing the  
> > polygns i am working with (file first_polygon.dat and files  
> > polygon_00.dat to polygon_15.dat). I also attached .off files  
> > storing the same polygons so you can visualize them.
> >
> > Thanks
> > Hichem
> >
> > ------------------------------------------------------------------------
> > *De :* 
> > ""
> >  
> > <>
> > *À :* 
> >
> > *Envoyé le :* Samedi, 26 Septembre 2009, 16h24mn 57s
> > *Objet :* Re: [cgal-discuss] An error when trying to compute  
> > intersection of polygons
> >
> > So you are trying to compute the intersection between  
> > 'first_polygon' and all the polygons in the range  
> > 'polygons.begin(), polygons.end()'. Could you please provide the  
> > data that causes the problem. It would be nice if you narrow it  
> > down first.
> >
> > Quoting "BBB HHH" 
> > <
> >  
> > <mailto:>>:
> >
> > > Hello,
> > >
> > > I am trying to compute the intersection of some polygons in 2D.  
> > For that purpose, i am using the 2D Regularized Boolean  
> > Set-Operations of CGAL 3.4. I am also using VS2005 under Windows XP  
> > SP3.
> > >
> > > For some polygons which seemto be correct (CCW orientation,  
> > non-degenerate, simple, bounded), i have the following error:
> > >
> > > CGAL error: precondition violation!
> > > Expression : cv.is_in_x_range (p)
> > > File      : c:\program  
> > files\cgal-3.4-beta1\include\cgal\arr_segment_traits_2.h
> > >
> > > Line      : 481
> > > Explanation:
> > > Refer to the bug-reporting instructions at  
> > http://www.cgal.org/bug_report.html
> > >
> > >
> > > I am using an exact kernel  
> > (CGAL::Simple_cartesian<CGAL::Lazy_exact_nt<Gmpq> >). The  
> > problematic line of code is that computing the intersection of some  
> > polygons
> > >
> > > std::vector<Polygon_2>        polygons;
> > > // Fill the list of polygons
> > > // Initialize the polygon set with a polygon
> > > Polygon_set_2 S(first_polygon);
> > > S.intersection(polygons.begin(), polygons.end());
> > >
> > > Thanks in advance for your help
> > > Hichem Barki
> > >
> > >
> > >
> > >      --
> > > You are currently subscribed to cgal-discuss.
> > > To unsubscribe or access the archives, go to
> > > https://lists-sop.inria.fr/wws/info/cgal-discuss
> > >
> >
> >
> > --You are currently subscribed to cgal-discuss.
> > To unsubscribe or access the archives, go to
> > https://lists-sop.inria.fr/wws/info/cgal-discuss
>
> --
> 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: 
>
> --
> You are currently subscribed to cgal-discuss.
> To unsubscribe or access the archives, go to
> https://lists-sop.inria.fr/wws/info/cgal-discuss