CGAL users discussion list

["Sebastien Loriot (GeometryFactory)" <>]

Try with

CGAL::polyhedron_cut_plane_3(result, he->opposite(), pl3);
instead of
CGAL::polyhedron_cut_plane_3(result, he, pl3);

he->vertex() need to be on the negative side of the plane.

S.

Max Harris wrote:
> polyhedron_cut_plane_3() breaks when I try running the code below. What 
> am I doing wrong?
>
> Here's the output:
> *Plane: -0 -1 -0 -0*
> **
> *Normal: -0 -1 -0*
> **
> *Scaled normal: -0 0.1 -0*
> **
> *Transformed plane: -0 -1 -0 0.1*
> *terminate called after throwing an instance of 
> 'CGAL::Precondition_exception'*
> *  what():  CGAL ERROR: precondition violation!*
> *Expr: pred( h->vertex())*
> *File: /usr/local/include/CGAL/polyhedron_cut_plane_3.h*
> *Line: 120*
>
> Root::Root()
> {
>     Polyhedron P;
>     make_cube_3(P);
>     Facet_iterator f = P.facets_begin(); 
>    
>     Plane pl2 = f->plane(); // plane equation of the facet
>     cout << "Plane: " << pl2 << endl;
>     
>     CGAL::Vector_3<Kernel> normal = pl2.orthogonal_vector();
>     cout << "\nNormal: " << normal << endl;
>     
>     Vector sn = normal.transform(Transformation(CGAL::SCALING, -0.1));
>     cout << "\nScaled normal: " << sn << endl;
>     
>     Plane pl3 = pl2.transform(Transformation(CGAL::TRANSLATION, sn));
>     cout << "\nTransformed plane: " << pl3 << endl;
>     
>     Polyhedron result;
>     Halfedge_handle he = make_cube_3(result);
>     
>     CGAL::polyhedron_cut_plane_3(result, he, pl3);
> }
>
>
> template <class Poly>
> typename Poly::Halfedge_handle Root::make_cube_3(Poly& P)
> {
>     // appends a cube of size [0,1]^3 to the polyhedron P.
>     CGAL_precondition( P.is_valid());
>     typedef typename Poly::Point_3         Point;
>     typedef typename Poly::Plane_3         Plane;
>     typedef typename Poly::Halfedge_handle Halfedge_handle;
>     Halfedge_handle h = P.make_tetrahedron(Point( 1, 0, 0),
>    Point( 0, 0, 1),
>    Point( 0, 0, 0),
>    Point( 0, 1, 0));
>     Halfedge_handle g = h->next()->opposite()->next();
>     P.split_edge( h->next());
>     P.split_edge( g->next());
>     P.split_edge( g);
>     h->next()->vertex()->point()     = Point( 1, 0, 1);
>     g->next()->vertex()->point()     = Point( 0, 1, 1);
>     g->opposite()->vertex()->point() = Point( 1, 1, 0);
>     Halfedge_handle f = P.split_facet( g->next(), 
> g->next()->next()->next());
>     Halfedge_handle e = P.split_edge( f);
>     e->vertex()->point() = Point( 1, 1, 1);
>     P.split_facet( e, f->next()->next());
>     CGAL_postcondition( P.is_valid());
>     g = h;
>     g->facet()->plane() = Plane( g->vertex()->point(),
> g->next()->vertex()->point(),
> g->next()->next()->vertex()->point());
>     g = h->opposite();
>     g->facet()->plane() = Plane( g->vertex()->point(),
> g->next()->vertex()->point(),
> g->next()->next()->vertex()->point());
>     g = h->next()->opposite();
>     g->facet()->plane() = Plane( g->vertex()->point(),
> g->next()->vertex()->point(),
> g->next()->next()->vertex()->point());
>     g = h->next()->next()->opposite();
>     g->facet()->plane() = Plane( g->vertex()->point(),
> g->next()->vertex()->point(),
> g->next()->next()->vertex()->point());
>     g = h->next()->next()->next()->opposite();
>     g->facet()->plane() = Plane( g->vertex()->point(),
> g->next()->vertex()->point(),
> g->next()->next()->vertex()->point());
>     g = g->next()->next()->opposite();
>     g->facet()->plane() = Plane( g->vertex()->point(),
> g->next()->vertex()->point(),
> g->next()->next()->vertex()->point());
>     return h;
> }
>
> On May 25, 2011, at 12:47 AM, Marc Glisse wrote:
>
> > On Wed, 25 May 2011, harris.max wrote:
> >
> > > I'm trying to get CGAL to generate a plane that's offset by some 
> > > specifiable
> > > distance from an existing plane, but everything I've tried so far isn't
> > > working. What's the best way to do this?
> >
> > What did you try that isn't working?
> >
> > There doesn't seem to be any function to do that directly, but you 
> > could for instance use Construct_orthogonal_vector_3 to get a normal 
> > vector, scale it to whatever distance you want, then translate the plane?
> >
> > --
> > Marc Glisse
> >
> > --
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