CGAL users discussion list

[Efraim Fogel <>]

Let me add and say that using an exact number type should not intimidate 
you. You can use the already defined kernel type 
CGAL::Exact_predicates_exact_constructions_kernel. This may already give 
you the performance you need.

If you are not going to construct new geometric objects (e.g., 
intersection points) at all. For example, if you intend to use the 
function CGAL::insert_non_intersecting_curve() and no other, use the 
kernel type  Exact_predicates_inexact_constructions_kernel, which is 
more efficient in this case.

Efi Fogel wrote:

> Jens Egeblad wrote:
>
> > Sorry to spam you like this.
> >
> > Ok, so as I suspected it seems like my problem has to do with 
> > precision. I thought arrangement_2 was very robust. Am I missing 
> > something?
>
>
> Arrangement_2, like the implementations of many other data structures 
> and algorithms of CGAL, is robust. Robustness is guarantied only if an 
> exact number type is used, and is achieved through the careful 
> handling of all degenerate cases.
>
> > I have been using doubles but I have no problem with MP_Float.
> >
> > I would really like to use an efficient number type since this is a 
> > performance critical applications.
> >
> > Is MP_Float efficient enough or does anyone have better idea?
>
>
> If your curves are linear (and you use a Cartesian kernel), you need a 
> rational number type. You could use CGAL::Quotient<CGAL::MP_Float>. 
> You can try CGAL::Gmpq, which is an adaptation of an exact rational 
> number type provided by GMP, and if you have access to Leda, you can 
> try leda::rational.
>
> > Best - Jens
> >
> > On 2/28/07, Jens Egeblad 
> > <>
> >  wrote:
> >
> > > Hi again
> > >
> > > I hope someone can help me out here... Anyway I did a little bit more
> > > research and these are the x/y-values of cv.left(), cv.right() and p.
> > >
> > > cv.left(): -4.241547e+01, 9.937383e-01,
> > > cv.right(): -4.241547e+01, 3.496869e+00,
> > > p: -4.241547e+01, 2.289501e+00
> > >
> > > Looks like it is a vertical edge, which seems a bit odd... Can 
> > > anyone help?
> > >
> > > - Jens
> > >
> > > On 2/28/07, 
> > >
> > >  
> > > <>
> > >  wrote:
> > > > Hi
> > > >
> > > > I get an assertion when I try to build an arrangement with a lot 
> > > of lines:
> > > >
> > > > CGAL error: precondition violation!
> > > > Expr: Segment_assertions::_assert_is_point_on (p, cv, 
> > > Has_exact_division()) && compare_xy(cv.left(), p) == SMALLER && 
> > > compare_xy(cv.right(), p) == LARGER
> > > > File: 
> > > /Users/jegeblad/CGAL_Install/include/CGAL/Arr_segment_traits_2.h
> > > > Line: 730
> > > > Abort trap
> > > >
> > > >
> > > > Does anyone know what could cause this problem? Could it be a 
> > > floating-point problem?
> > > >
> > > > Best - Jens
> > > >
> > > > --
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> > > >


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