CGAL users discussion list

["J.L.M." <>]

I just tried the kernel you suggested and I get the same problem.

terminate called after throwing an instance of 'CGAL::Assertion_exception'
  what():  CGAL ERROR: assertion violation!
Expr: Ntmp.is_valid()
File: 
/import/lightcycle/home/jlm/school/masters_thesis/code/CGAL-3.7/include/CGAL/Minkowski_sum_3/bipartite_nary_union_sorted_combined.h
Line: 222
Aborted

On 01/24/2011 03:10 AM, Sebastien Loriot (GeometryFactory) wrote:
> I add a quick look but did not have time to finish my investigations.
> Can you try with CGAL::Simple_cartesian<CGAL::Gmpq> as Kernel and tell
> us whether you also observe the same problems?
>
> S.
>
>
> J.L.M. wrote:
> > I was wondering if any progress has been made to fix the boundary
> > function for Nef_polyhedron_3. I am using this code in a thesis, and I
> > am finding that I can not avoid the assertion in the Minkowski_sum_3
> > if I use a non-convex polyhedron. Limiting my input to convex
> > polyhedra greatly reduces the utility of my implementation, and my
> > experiment depends on non-convex polyhedra.
> >
> > Thank you for your time.
> >
> > Jason M'Sadoques
> >
> > On 12/27/2010 04:32 PM, J.L.M. wrote:
> > > Sebastien,
> > >
> > > Thank you for your reply. I have been on holiday, or I would have
> > > responded sooner. I hope you will be able to provide a fix to the
> > > boundary function, as this is essential to my research. If there is
> > > anything I can do to help, please let me know.
> > >
> > > Here are a few responses to your statements. The call to boundary is
> > > necessary for my work. What I am computing is the feasible region that
> > > contains all points in which the object can be placed and be wholly
> > > contained in the container (stored in result). If you would like, I have
> > > a paper I can provide to you that shows how this works.
> > >
> > > Second, I am wondering about your statement that I need to make a copy
> > > of container. I see that the minkowski_sum_3 modifies the input, and in
> > > my example code the input is container_boundary, and object.
> > > container_boundary should be a copy of container (well just the boundary
> > > of course).
> > >
> > > You are correct that the result is empty in this example. The correct
> > > algorithm uses the interior of the object (actually the inverted
> > > interior) in the Minkowski sum. I removed that part while simplifying
> > > the code to one that shows the problem.
> > >
> > > Thank you for pointing out the non-standard OFF files. I am creating my
> > > shapes in Blender, and I have to post-process them. First, Blender gives
> > > me coordinates that are something like 1.00001 or 0.99999, and I need
> > > them to be exact whole numbers for accurate computations. Also, Blender
> > > has Z increase up, and Y increase into the scene, which is different
> > > than I am used to with OpenGL, so I swapped those coordinates. It must
> > > be in my swapping of those that I have switched the orientation of the
> > > facets.
> > >
> > > Thank you again for your time.
> > >
> > > On 12/20/2010 08:26 AM, Sebastien Loriot (GeometryFactory) wrote:
> > > > J.L.M. wrote:
> > > > > I have been writing some programs that use the Nef_polyhedron_3 and
> > > > > Minkowski_sum_3 portions of the CGAL library. I have discovered a
> > > > > number of assertions with various input shapes. The attached backtrace
> > > > > shows one example problem. I have also attached a small example
> > > > > program, and the input shapes. The l-shape is shown in the attached
> > > > > jpeg file.
> > > > >
> > > > > This problem shows up in both CGAL 3.7 and 3.6.1. I am using GCC 4.5.1
> > > > > on Arch Linux with kernel version 2.6.36.
> > > > >
> > > > > I think this is a bug, since it does not occur with other input
> > > > > shapes. I would be very grateful if someone can help me fix it since
> > > > > the Minkowski_sum_3 is essential to my research.
> > > > >
> > > > > Thank you for your time.
> > > > >
> > > > > Jason M'Sadoques
> > > > >
> > > > >
> > > > >
> > > > > ------------------------------------------------------------------------
> > > > It seems their is a problem in boundary function.
> > > >
> > > > If I replace:
> > > > Nef_polyhedron_3 container_boundary(container.boundary());
> > > > by
> > > > Nef_polyhedron_3 container_boundary(container);
> > > >
> > > > Your program runs fine (with your data, the call to boundary is
> > > > superfluous).
> > > >
> > > > Note that as you are then reusing "container", you need to make a copy
> > > > of it
> > > > (see
> > > > http://www.cgal.org/Manual/latest/doc_html/cgal_manual/Minkowski_sum_3/Chapter_main.html)
> > > >
> > > >
> > > >
> > > >
> > > > Note also that the difference you are computing will be empty as the
> > > > Minkowski sum contains "container".
> > > >
> > > > Finally, note that facets of your cube are clockwise oriented while the
> > > > usual convention is to use counterclockwise oriented faces in off
> > > > files.
> > > >
> > > > I'll try to find a fix to boundary function and will post it here.
> > > >
> > > > S.