CGAL users discussion list

[Edgar Simo-Serra <>]

Hello,


Ah thank you. It works great. I had erroneously thought that I could use
inexact_constructions in order to go a bit faster, but it seems like I
was wrong.

Thanks,


Edgar

On 2012年09月23日 15:49, Efi Fogel wrote:
> You are doing something wrong.
> 
> First of all, you are joining polygons, which means that new
> intersection points might be constructed. Therefore, you must use
> Exact_predicates_exact_constructions_kernel kernel (instead of the
> Exact_predicates_inexact_constructions_kernel kernel currently used in
> your example).
> 
> Even if you had known that no new intersection points are expected to be
> constructed you would have still needed to use the
> Exact_predicates_exact_constructions_kernel kernel, as explained next.
> The code that you write implicitly uses the Arr_segment_traits_2. This
> traits maintains a segment by its 2 endpoints and the underlying line.
> The constructor of the segments accepts the 2 endpoints as input
> arguments and CONSTRUCTS the underlying line. Therefore, you must use
> the Exact_predicates_exact_constructions_kernel kernel.
> 
> I've tried it and it works.
> 
> On Thu, Sep 20, 2012 at 12:40 PM, bobbens 
> <
> <mailto:>>
>  wrote:
> 
>     Hello,
> 
> 
>     I'm not sure if I'm doing something wrong, but I am getting precondition
>     failures on attempting to join 4 different simple polygons with 4
>     vertices
>     each. I'm attaching the code to reproduce (must compile in debug
>     mode) and a
>     visual representation of the four polygons. They are being joined as
>     part of
>     a polygon set.
> 
>     With CGAL 3.9 (Ubuntu 12.04) I get:
> 
>     terminate called after throwing an instance of
>     'CGAL::Precondition_exception'
>       what():  CGAL ERROR: precondition violation!
>     Expr: cv.is_in_x_range (p)
>     File: /usr/include/CGAL/Arr_segment_traits_2.h
>     Line: 487
> 
>     With CGAL 4.0 (Arch linux) I get:
> 
>     terminate called after throwing an instance of
>     'CGAL::Precondition_exception'
>       what():  CGAL ERROR: precondition violation!
>     Expr: comp_f(object, parentP->object) != SMALLER
>     File: /usr/include/CGAL/Multiset.h
>     Line: 2128
> 
>     So my main question is, am I doing something wrong? I was under the
>     impression that the join should work. This is part of a larger framework
>     that works on many other cases but seems to fail in this particular
>     one. The
>     code for the minimal reproduction case is very simple as can be seen.
> 
>     Thanks,
> 
> 
>     Edgar
> 
>     poly_precond.cpp
>     
> <http://cgal-discuss.949826.n4.nabble.com/file/n4655881/poly_precond.cpp>
>     polygons.png
>     <http://cgal-discuss.949826.n4.nabble.com/file/n4655881/polygons.png>
> 
> 
> 
> 
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