CGAL users discussion list

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

Thanks for the help. Unfortunately, changing the kernel does not alter 
the output. I am still getting the same behavior using an 
Exact_predicate_exact_construction_kernel. That is, in the line case, 
the same polygon is being produced, and in the point case, the program 
is still going into an infinite loop.

The change I did was to add this line:

#include <CGAL/Exact_predicates_exact_constructions_kernel.h>

And change my Kernel typedef to:

typedef CGAL::Exact_predicates_exact_constructions_kernel Kernel;


 wrote:
> As Ben pointed out, you must use an exact-predicate and 
> exact-construction kernel. I suggest:
>
> CGAL::Exact_predicate_exact_construction_kernel
>
> Quoting "Ben Supnik" 
> <>:
>
> > Hi JLM,
> >
> > Am I right in thinking that you are using a kernel that does not have 
> > exact constructions with Minkowski sum?
> >
> > I'm not 100% sure on this, but I think you need an exact construction 
> > kernel to use Minkowski sums.
> >
> > cheers
> > Ben
> >
> >
> >
> > J.L.M. wrote:
> > > Attached are two simple programs that demonstrate my difficulties 
> > > with 2D Minkowski sums. The first one, mks_point.cpp enters into an 
> > > infinite loop when attempting to calculate the Minkowski sum of one 
> > > polygon with another polygon that contains only one single point. It 
> > > is my expectation that the result of such a computation is merely the 
> > > translation of the polygon by the point.
> > >
> > > Secondly, and more important to me, I need to calculate the Minkowski 
> > > sum of a polygon and an edge of another polygon. I am doing that by 
> > > making a polygon with only two verticies. The second program shows my 
> > > problem. The output is:
> > >
> > > { Outer boundary = [ 14 vertices: (-7 -3) (-7 -13) (-13 -13) (-13 -3) 
> > > (-17 -3) (-27 -3) (-27 -17) (-3 -17) (7 -17) (7 -3) (3 -3) (7 -3) (7 
> > > -17) (-3 -17) ]
> > >  0 holes:
> > > }
> > >
> > > Which is incorrect. The last three verticies should not exist, and if 
> > > you look closely, they backtrack along the path around the polygon. 
> > > When I use the verticies in an OpenGL program to display the polygon, 
> > > I get a nonsensical shape. If those last three verticies were not 
> > > there, then the shape would be correct. It is a U shape with square 
> > > corners, translated horizontally. So the vertical parts of the U 
> > > shape should be thick due to the translation.
> > >
> > > When I remove the negative signs from the Q polygon, then the output 
> > > is correct.
> > >
> > > I would appreciate some help with this. I did not see anything in the 
> > > CGAL manual stating that there were restrictions on the Minkowski sum 
> > > operation.
> > >
> > > Thanks.
> >
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