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[yanyajie <>]

Hi,

 

I encounterd a precondition violation error when I was trying to find the intersection between a line and a sphere.

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CGAL error: precondition violation!

_expression_ : !p.degenerated()

File       : d:\codes\lib\cgal-3.7\include\cgal\algebraic_kernel_for_spheres\int

ernal_functions_on_roots_and_polynomial_1_3_and_2_3.h

Line       : 212

Explanation:

Refer to the bug-reporting instructions at http://www.cgal.org/bug_report.html

-------------------------------------------------------------------------------------

 

I provide necessary info in the following to help reproduce the error:

 

------------------------------------------------------------------------------------------------------------------------------------------------------

typedef CGAL::Cartesian<double> K;

typedef CGAL::Spherical_kernel_3<K, CGAL::Algebraic_kernel_for_spheres_2_3<int> > SphericalK;

typedef SphericalK::Point_3 Point_3_SK;

 

// to compute the intersection, I construct a line and a sphere using the spherical kernel as follows:

CGAL::Line_3<SphericalK> line(Point_3_SK(-0.1,-0.1,-0.1), Point_3_SK(-0.1,-0.1,0.0));

CGAL::Sphere_3<SphericalK> s(Point_3_SK(0, 0, 0), 0.1); // c is a Point_3

vector<CGAL::Object> isecs;

CGAL::intersection(line, s, std::back_inserter(isecs));

------------------------------------------------------------------------------------------------------------------------------------------------------

 

The assertion error is issued from within CGAL::intersection, when it tries to do the confirmation,

actually, from this function:

 

template < class AK, class OutputIterator >

inline

OutputIterator

    solve(const typename AK::Polynomials_for_line_3 &p,

          const typename AK::Polynomial_for_spheres_2_3& s,

     OutputIterator res )

{

...

// we must have a line

CGAL_kernel_precondition(!p.degenerated());

...

}

 

 

Does this failure of assertion indicates I constructed a degenerate line? But from the code you can see the line should be non-degenerate.

 

Thanks if anyone can point out the problem!

 

 

Yan.