CGAL users discussion list

["Sebastien Loriot (GeometryFactory)" <>]

On 02/08/2013 08:41 PM, Jeffrey Bush wrote:
> I was hoping to do something while still using doubles, which is why I
> went for Exact_predicates_inexact_constructions_kernel.
Unfortunately all rational numbers cannot be represented using double to 
there is no chance that the intersection of your polyhedron with a
plane is exactly on the polyhedron. One solution is to insert the 
intersection segments inside the polyhedron.

> I just tried
> Exact_predicates_exact___constructions_kernel like you suggested, but I
> get the following exception:
>
> CGAL error: assertion violation!
> Expression : !(i>s)
> File       : C:\CGAL\CGAL-4.1\include\CGAL/Interval_nt.h
> Line       : 90
> Explanation:  Variable used before being initialized (or CGAL bug)
> Refer to the bug-reporting instructions at
> http://www.cgal.org/bug_report.html

I would need a minimal example showing the problem to debug this.

Sebastien.

> The stack trace is:
> CrossSectionCGAL.exe!CGAL::Interval_nt<0>::Interval_nt<0>(double i,
> double s)  Line 94C++
> CrossSectionCGAL.exe!CGAL::Interval_nt<0>::operator-()  Line 99 + 0x6d
> bytesC++
> CrossSectionCGAL.exe!CGAL::PlaneC3<CGAL::Simple_cartesian<CGAL::Interval_nt<0>
>  > >::opposite()  Line 269 + 0x1a bytesC++
> CrossSectionCGAL.exe!CGAL::CommonKernelFunctors::Construct_opposite_plane_3<CGAL::Simple_cartesian<CGAL::Interval_nt<0>
>  > >::operator()(const
> CGAL::Plane_3<CGAL::Simple_cartesian<CGAL::Interval_nt<0> > > & p)  Line
> 1254 + 0x3f bytesC++
> CrossSectionCGAL.exe!CGAL::Lazy_rep_1<CGAL::Plane_3<CGAL::Simple_cartesian<CGAL::Interval_nt<0>
>  > >,CGAL::Plane_3<CGAL::Simple_cartesian<CGAL::Gmpq>
>  >,CGAL::CommonKernelFunctors::Construct_opposite_plane_3<CGAL::Simple_cartesian<CGAL::Interval_nt<0> > >,CGAL::CommonKernelFunctors::Construct_opposite_plane_3<CGAL::Simple_cartesian<CGAL::Gmpq> 
> >,CGAL::Cartesian_converter<CGAL::Simple_cartesian<CGAL::Gmpq>,CGAL::Simple_cartesian<CGAL::Interval_nt<0> >,CGAL::NT_converter<CGAL::Gmpq,CGAL::Interval_nt<0> > >,CGAL::Plane_3<CGAL::Epeck> 
> >::Lazy_rep_1<CGAL::Plane_3<CGAL::Simple_cartesian<CGAL::Interval_nt<0> > >,CGAL::Plane_3<CGAL::Simple_cartesian<CGAL::Gmpq> 
> >,CGAL::CommonKernelFunctors::Construct_opposite_plane_3<CGAL::Simple_cartesian<CGAL::Interval_nt<0> > >,CGAL::CommonKernelFunctors::Construct_opposite_plane_3<CGAL::Simple_cartesian<CGAL::Gmpq> 
> >,CGAL::Cartesian_converter<CGAL::Simple_cartesian<CGAL::Gmpq>,CGAL::Simple_cartesian<CGAL::Interval_nt<0> >,CGAL::NT_converter<CGAL::Gmpq,CGAL::Interval_nt<0> > >,CGAL::Plane_3<CGAL::Epeck> >(const 
> CGAL::CommonKernelFunctors::Construct_opposite_plane_3<CGAL::Simple_cartesian<CGAL::Interva
l_nt<0> > > & ac, const 
CGAL::CommonKernelFunctors::Construct_opposite_plane_3<CGAL::Simple_cartesian<CGAL::Gmpq> > & ec, const 
CGAL::Plane_3<CGAL::Epeck> & l1)  Line 354 + 0x6d bytesC++
> CrossSectionCGAL.exe!CGAL::Lazy_construction<CGAL::Epeck,CGAL::CommonKernelFunctors::Construct_opposite_plane_3<CGAL::Simple_cartesian<CGAL::Interval_nt<0>
>  >
>  >,CGAL::CommonKernelFunctors::Construct_opposite_plane_3<CGAL::Simple_cartesian<CGAL::Gmpq> 
> >,CGAL::Default,1>::operator()<CGAL::Plane_3<CGAL::Epeck> >(const CGAL::Plane_3<CGAL::Epeck> 
> & l0)  Line 1381 + 0xbf bytesC++
>
> ... (a few really long lines)
>
> CrossSectionCGAL.exe!CGAL::Polyhedron_3<CGAL::Epeck,CGAL::Polyhedron_items_3,CGAL::HalfedgeDS_default,std::allocator<int>
>  >::inside_out_geometry(CGAL::Boolean_tag<1> __formal)  Line 1474C++
>  
> >CrossSectionCGAL.exe!CGAL::Polyhedron_3<CGAL::Epeck,CGAL::Polyhedron_items_3,CGAL::HalfedgeDS_default,std::allocator<int>
>  >::inside_out()  Line 1482C++
>
>
> Jeff
>
>
> On Thu, Feb 7, 2013 at 9:59 PM, Sebastien Loriot (GeometryFactory)
> <
>  
> <mailto:>>
>  wrote:
>
>     Check this FAQ entry:
>     http://www.cgal.org/FAQ.html#__inexact_NT
>     <http://www.cgal.org/FAQ.html#inexact_NT>
>
>     If you use Exact_predicates_exact___constructions_kernel.h this
>     should be OK.
>
>     Even if it's not documented and not officially supported, I suggest
>     you to have a look at the file CGAL/intersection_of___Polyhedra_3.h
>
>     where the following function is defined:
>
>     template <typename Polyhedron, typename OutputIterator>
>     OutputIterator
>     intersection_Polyhedron_3___Polyhedron_3(const Polyhedron& P, const
>     Polyhedron& Q, OutputIterator out)
>
>     where OutputIterator accepts std::vector<typename Kernel::Point_3>
>     objects (to represent a polyline).
>
>     A plane can always be represented by a triangulated quad.
>
>     Sebastien.
>
>
>
>     On 02/08/2013 12:31 AM, Jeffrey Bush wrote:
>
>         Hi,
>
>         I am using AABB_tree to determine intersections between a plane
>         (call it
>         "h") and a polyhedron, resulting in a vector of segments ("segs").
>         However the following test fails:
>
>              h.has_on(*segs.begin())
>
>
>         This shouldn't be. However doing research I realized the result
>         may be
>         because of using Cartesian instead of
>         Exact_predicates_inexact___constructions_kernel, so I switched
>         to that.
>         But still the same problem!
>
>         Running the debugger I get to this function:
>
>             inline
>             Uncertain<Sign>
>             sign (const  Interval_nt<Protected> &  d)
>             {
>               if  (d.inf()>  0.0)return  POSITIVE;
>               if  (d.sup()<  0.0)return  NEGATIVE;
>               if  (d.inf() == d.sup())return  ZERO;
>
>               return  Uncertain<Sign>::__indeterminate();
>             }
>
>         With the following value for d:
>
>         d = {
>             _inf=5.6843418860808015e-014,
>             _sup=5.6843418860808015e-014,
>             tester={...}
>         }
>
>         It seems as though the d.inf() == d.sup() check should be first? It
>         seems that if sup <= inf and inf > 0 or sup < 0, then the d.inf() ==
>         d.sup() can only be 0 == 0... (but I guess sup > inf - I don't
>         understand exactly what this is all about).
>
>         Just for scale, my points have values on the order of 2500 and
>         the plane
>         is <0,0,1> -300.
>
>         If this is right (and I could easily be, I don't know too much about
>         double-precision mathematical testing), then what am I doing
>         wrong? My
>         meshes are LARGE so I don't want to use the infinite-precision
>         numbers.
>
>         Thanks!
>         Jeff
>
>
>
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