CGAL users discussion list

[Efraim Fogel <>]

In the example, there is a call to 
CGAL::get_intersection_points().However, in the more recent version this 
call does not exist, as it has been replaced by 
CGAL::compute_intersection_points().

I suspect you are using an older version, which may be buggy. We tested 
the code with the new version and it works fine.

P.S.
In the original example code there is a problem with the printf() call, 
and the argument *n,* should be added after the format string in order 
to get a proper output.

Ben Supnik wrote:
> Hi Y'all,
>
> I am using get_intersection_points_2 to try to find all places where 
> bezier curves intersect each other (excluding end-points) - I am using 
> the standard bezier curve traits from the arrangement package (e.g. 
> from the demo code) with CORE for my numeric type.
>
> The surprising result is that if I pass in 4 curves (each with only 
> two control points, so they are really line segments) I get an 
> assertion failure at Bezier_bounding_rational_trait:247... there are 5 
> intersection pairs, not just 1.
>
> My "curves" are really quite boring...just a bow-tie shape.
>
> Are there any known gotchas here?  I've posted a heavily cut down 
> sample reproducer here:
>
> http://dev.x-plane.com/download/test_bez.cpp
>
> "interesting" part of the code is at the end of the email.  The output 
> gives me:
>
> CGAL error: assertion violation!
> Expr: intersection_pairs.size() == 1
> File: 
> ../../libs/local/include/CGAL/Arr_traits_2/Bezier_bounding_rational_traits.h 
>
> Line: 247
> Explanation:
> terminate called after throwing an instance of 
> 'CGAL::Assertion_exception'
>   what():  CGAL ERROR: assertion violation!
> Expr: intersection_pairs.size() == 1
> File: 
> ../../libs/local/include/CGAL/Arr_traits_2/Bezier_bounding_rational_traits.h 
>
> Line: 247
> Abort trap
> mac-pro:XESTools bsupnik$ scp test_bez.cpp 
> :/shared/download/test_bez.cpp
>
> Anyway, if I am doing something really, really idiotic, please let me 
> know!!
>
> cheers
> ben
>
>
>     vector<Rat_point_2>    c;
>     vector<Bezier_curve_2> curves;
>     vector<Bezier_point_2>    p;
>     
>     c.resize(2);
>     c[0] = Rat_point_2(-71.026688,42.395582);
>     c[1] = Rat_point_2(-71.011037,42.396439);
>     curves.push_back(Bezier_curve_2(c.begin(),c.end()));
>
>     c[0] = Rat_point_2(-71.011037,42.396439);
>     c[1] = Rat_point_2(-71.010892,42.390653);
>     curves.push_back(Bezier_curve_2(c.begin(),c.end()));
>
>     c[0] = Rat_point_2(-71.010892,42.390653);
>     c[1] = Rat_point_2(-71.022341,42.400083);
>     curves.push_back(Bezier_curve_2(c.begin(),c.end()));
>
>     c[0] = Rat_point_2(-71.022341,42.400083);
>     c[1] = Rat_point_2(-71.026688,42.395582);
>     curves.push_back(Bezier_curve_2(c.begin(),c.end()));
>
>     Bezier_traits_2 traits;
>     CGAL::get_intersection_points(curves.begin(),curves.end(),
>         back_inserter(p), false, traits);
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