CGAL users discussion list

[Frederic De Pourcq <>]

Hi again, 

Ok, I found out what I did wrong:

* my offset was wrong, resulting in the exception, the plane must have been 
outside.
* my halfedge wasn't passing through the plane, if it doesn't the program 
gets 
stuck in a loop.
* the halfedge had to come from the correct side, I had to invert the plane 
or 
use the opposite of my halfedge. If this is not done a segfault occurs.

Greetings,

F!


On Tuesday 24 February 2009 01:16:05 

 wrote:
> Hi,
>
> I am writing code that constructs bsp-trees. For this I need a robust way
> of cutting polyhedra (K-dops, K-discrete oriented polytopes) using a plane.
> Given a plane description and a polyhedron I want 2 polyhedra back. As
> simple as cutting a block of cheese in 2 with a knife.
>
> I could not find a solution to my problem in the documentation, but I did
> find the function polyhedron_cut_plane_3  in header
> CGAL/polyhedron_cut_plane_3.h
>
> I also found an example program for it:
> Polyhedron/polyhedron_prog_cut_cube.cpp That example works, but when trying
> to use different splitting planes I get problems.
>
> Plane  pl = Plane(0,1,0,0.5 );        // orientation (0,1,0) offset 0.5, 
> straight
> through the [0,1]^3 cube
>
> ERROR: coplanar planes used for computing intersecting point.
>        Return ORIGIN. Don't trust result.
> ERROR: coplanar planes used for computing intersecting point.
>        Return ORIGIN. Don't trust result.
>
> And it does not modify the given polyhedron.
>
> What is going on? A cutting function that can not cut a cube in 2 equal
> halves? How can I get rid of this problem?
>
> Any help is appreciated,
>
> Thanks,
>
> F!