CGAL users discussion list

["Sebastien Loriot (GeometryFactory)" <>]

On 11/06/2014 06:25 PM, Илья Палачев wrote:
> Hi,
> Thanks for answers.
> I'm not the first who asks about this function, so maybe it will be
> worthwhile to include halfspaces_intersection.h to official CGAL source
> code?

It should be included in the next release of CGAL thanks to the work
of Jocelyn during his Google Summer of Code internship.

Sebastien.

> Best regards,
> Ilya Palachev
> 06.11.2014, 12:11, "Quentin Merigot" 
> <>:
> > Hi,
> >
> > I did not try actually running your code, but there is no reason why
> > the convex hull of a set of points should be *strongly* convex, which
> > means that all points are extreme points (think of the convex hull of
> > the eight vertices of a cube, plus a point that lies on one of the
> > facets of the cube: the ninth point is not an extreme point, but
> > nonetheless belongs to the convex hull).
> >
> > Best,
> > Quentin
> >
> > 2014-11-05 19:20 GMT+01:00 Илья Палачев 
> > <
> > <mailto:>>:
> >
> >     Hi,
> >     I'm using 4.3 version of CGAL. Do you advise to update it?
> > >     Ilya uses 'true' for the second parameter:
> >     I did not change anything in Quentin's code except one that line.
> >     BTW, I've found another issue related with this function.
> >     After construction of the intersection, the assertion
> >     is_strongly_convex_3 fails.
> >     Here is my code:
> >     static VectorXd buildStartingVector(SupportFunctionDataPtr data)
> >     {
> >     // Some code
> >     /* Construct intersection of support halfspaces represented by
> >     planes */
> >     std::vector<Plane_3> planes = data->supportPlanes();
> >     Polyhedron_3 intersection;
> >     globalPCLDumper(PCL_DUMPER_LEVEL_DEBUG,
> >     ".support-planes-for-halfspaces_intersection.txt")
> >     << planes;
> >     CGAL::internal::halfspaces_intersection(planes.begin(), planes.end(),
> >     intersection, Kernel());
> >     ASSERT(is_strongly_convex_3(intersection));
> >             // Some code
> >     }
> >     I have printed planes to file and attached them to this mail. Here
> >     is the way they were printed:
> >     std::ostream &operator<<(std::ostream &stream,
> >     std::vector<Plane_3> planes)
> >     {
> >     for (auto plane = planes.begin(); plane != planes.end(); ++plane)
> >     stream << plane->a() << " " << plane->b() << " " << plane->c()
> >     << " " << plane->d() << std::endl;
> >     return stream;
> >     }
> >     It is interesting that even if I remove check
> >     "ASSERT(is_strongly_convex_3(intersection))" and if I get the hull
> >     of its points, the assertion also fails:
> >     Polyhedron_3 hull;
> >     std::vector<Point_3> points;
> >     for (auto vertex = intersection.vertices_begin();
> >     vertex != intersection.vertices_end(); ++vertex)
> >     {
> >     points.push_back(vertex->point());
> >     }
> >     CGAL::convex_hull_3(points.begin(), points.end(), hull);
> >     ASSERT(is_strongly_convex_3(hull));
> >     Do you think that upgrade to CGAL 4.5 can resolve this issue?
> >     Best regards,
> >     Ilya
> >     03.11.2014, 19:14, "Laurent Rineau (CGAL/GeometryFactory)"
> >     
> > <
> >  
> > <mailto:>>:
> > >     Le Monday 03 November 2014 15:23:09 Quentin Merigot a écrit :
> > >
> > >          Thank you for this bug report, it is now fixed in my
> > >         repository. However, I
> > >          must say that I am surprised that it did not work before
> > >         this change: the
> > >          numbers provided to the constructor of
> > >         Polyhedron_incremental_builder_3 are
> > >          in principle only used as estimations to reserve memory.
> > >         What version of
> > >          CGAL are you using ?
> > >
> > >     The constructor of CGAL::Polyhedron_incremental_builder has a
> > >     second parameter
> > >     that is a Boolean:
> > >     
> > > http://doc.cgal.org/latest/Polyhedron/classCGAL_1_1Polyhedron__incremental__builder__3.html#acb8216ef40323e777f57cd4656d98c83
> > >
> > >     When it is set to 'true', then that class template does extra
> > >     checks, and
> > >     display diagnostics.
> > >
> > >     Ilya uses 'true' for the second parameter:
> > >
> > >                typename CGAL::Polyhedron_incremental_builder_3<HDS>
> > >         B( hds, true);
> > >
> > >                B.begin_surface(_primal.size_of_facets(),
> > >                                _primal.size_of_vertices(),
> > >                                _primal.size_of_vertices());
> > >
> > >     That explains the reported behavior.
> > >
> > >     --
> > >     Laurent Rineau, PhD
> > >     R&D Engineer at GeometryFactory http://www.geometryfactory.com/
> > >     Release Manager of the CGAL Project http://www.cgal.org/
> > >
> > >
> > >     --
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