CGAL users discussion list

[Efraim Fogel <>]

During the computation of Minkowski sums new points might be
constructed. These points are used as operands of predicates. Thus, you
need an exact-construction kernel (as well as an exact-predicate
kernel). I didn't understand the second question.

jim.wilenius wrote:
> Hi!
>  
>  I am using the CGAL lib in OSX 10.6. (freshly compiled, I followed the
> instructions carefully)
>
> I am using the CGAL::Exact_predicates_inexact_constructions_kernel and when
> running minkowski sum 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/local/include/CGAL/Arr_segment_traits_2.h
> Line: 486
> ---
>
> I get the error given the following two polygons (in order):
>
> P:
> 4
> 0.0 0.0
> 29.809108311772626 0.0
> 29.809108311772626 29.809108311772626
> 0.0 29.809108311772626
>
> Q:
> 7
> 99.10004234616522 202.2922116762398
> 168.16528534816382 202.2922116762398
> 168.16528534816382 271.3574546782384
> 154.3522367477641 271.3574546782384
> 140.53918814736437 243.73135747743896
> 126.72613954696467 229.91830887703924
> 99.10004234616522 216.1052602766395
>
> I am not sure exactly what the error means? Is it supposed to give an error?
> If I use CGAL::Exact_predicates_exact_constructions_kernel then I do not get
> the error.
>
> using exact constructions is extremely slow for my application, so I would
> really like to use inexact.
>
> by the way, how inexact is the inexact kernel? Any pointers to useful info
> is welcome.
>
> Regards,
> Jim
>   
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