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[Max Harris <>]

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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