CGAL users discussion list

[Priyank Jain <>]

Hi Andreas,

I understand that, but I thought when I make the polyhedron, the plane 
is generated and stored within.

So, when I do this:

Polyhedron model;
Point_3 p( 1.0, 0.0, 0.0);
Point_3 q( 0.0, 1.0, 0.0);
Point_3 r( 0.0, 0.0, 0.0);
model.make_triangle(p, q, r);

Wouldn't the plane (formed due to the triangle) be generated / 
initialiazed automatically ?

Thanks
/Priyank

Andreas Fabri wrote:
> Hi Priyank,
>
> You have to initialize the plane yourself. The Polyhedron only 
> provides the storage.
>
> andreas
>
> Priyank Jain wrote:
> > I am always getting a degenerate plane, when I try to find out the 
> > plane from the given half-edge in Polyhedron data structure. Any 
> > guesses why ???
> >
> > for(Halfedge_iterator hedge_it = model.halfedges_begin() ; hedge_it !=
> > model.halfedges_end(); hedge_it++)
> > {
> > // proceed for boundary edges
> > if( hedge_it->is_border() == false) // boundary(hedge_it)
> > continue;
> >
> > // find x_proj by:
> > // "projecting_distance" perpendicular to "hedge_it" from the midpoint
> > of hedge_it
> > // in the plane of the model at hedge_it
> > // Finding the midpoint: midPt
> > Point_3& point1 = hedge_it->vertex()->point();
> > Point_3& point2 = hedge_it->opposite()->vertex()->point();
> > Point_3& midPt = midpoint(point1, point2);
> >
> > Plane& plane = hedge_it->opposite()->face()->plane(); //opposite
> > half-edge since this gives the plane of the model at that edge
> > Vector3& direction = plane.orthogonal_vector();
> >
> > //debugging purposes
> > Point_3 pt = plane.point();
> > bool waste = false;
> > waste = plane.is_degenerate();
> >
> > //Vertex_3 x_proj = hedge_it.project(midpoint, projecting_distance);
> > Point_3& x_proj = midPt + (direction * projecting_distance);
> > }
> >
> > waste (degenerate plane) always becomes true, why ? I tried different 
> > values
> > of
> > vertices, but still..
> >
> > Polyhedron model is made up of:
> > Point_3 p( 1.0, 0.0, 0.0);
> > Point_3 q( 0.0, 1.0, 0.0);
> > Point_3 r( 0.0, 0.0, 0.0);
> > model.make_triangle(p, q, r);
> >
> > Can someone please help me with this?
> >
> > Thanks