CGAL users discussion list

["Kenneth Tham" <>]

Hi,
   Thanks for your help. I am now trying to debug the algorithm for joining 
the polygons. There is one case where it needs to merge about 300 polygons. 
After about 200 times, the program gives the error as shown in the attached 
file. I'm not really sure what it means. Can anybody help? Thanks.
Regards,
Kenneth



-----Original Message-----
From: Efi Fogel 
[mailto:]
Sent: Tuesday, February 12, 2008 10:23 PM
To: 

Subject: Re: [cgal-discuss] CGAL::join Function


Kenneth Tham wrote:

>Hi,
>    I am using the CGAL::join function for joining polygon_with_holes_2 
> objects. In my program, I use the join function for about 10000 times 
> consequtively(trying to join a polygon to a set of polygons). My program 
> takes quite a long time to process this part ( several minutes ). Is it 
> normal for this function to take this amount of time? Thanks.   
>Regards,
>Kenneth
>
>  
>
First of all you should call the join function just once with a range of
input polygons (or polygons with holes). If you intend to perform other
operations in a sequence, you should call the join member function of
Polygon_set_2 instead of the global join function. Finally, I assume you
are using a exact-prediacte exact-construction kernel (for a good
reason). This means that all operations are caried out in an exact
maner. You can try to expedite the computation by reducing the bit
length of the input coordinates.

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CGAL error: precondition violation!                                           
  
Expr: compare_xy(cv1.right(), p) == LARGER && compare_xy(cv2.right(), p) == 
LARGER                                                                        
      
File: c:\program files\cgal-3.3.1\include\cgal\arr_segment_traits_2.h         
  Line: 609