CGAL users discussion list

["Vincent Wolowski" <>]

Hello Ash,

thanks a lot for your comments!
I guess, I got confused about the convex hull (sigh).

As you said,
[...]
std::vector<K::Point_3> points;
points.push_back(K::Point_3(4.0, 11.0, 0.0));
points.push_back(K::Point_3(5.0, 6.0, 0.0));
[...]
Polyhedron_3 polyhedron;
CGAL::convex_hull_3(points.begin(), points.end(), polyhedron);
for (Vertex_iterator v = polyhedron.vertices_begin(); v !=
polyhedron.vertices_end(); ++v) {
   std::cout << v->point() << std::endl;
}
[...]
works just fine to get the vertices of the convex hull.

> Since you mention the points are in 3D, I'm guessing you want the volume
> when you mention "area they are all part of". I don't know if CGAL
> provides the volume of a polyhedron. OTOH if you want the area of the
> boundary, you could sum up the areas of the boundary facets.

I will project them into 2D and then calculate the area.
That will fit what I need.
But thank you for your comment.

Best regards,
Vincent


On Nov 29, 2007 12:17 PM, Ashwin Nanjappa 
<>
 wrote:
> Vincent Wolowski wrote:
> [...]
> > I have a set of points in 3D, for which I would like to calculate an
> > area, they are all part of, and determine which points are on the
> > edge/boundary of the area.
> > In CGAL I found an implementation for convex hull which could be suitable.
> > But I cannot find any method that would allow to determine the
> > edge/boundary of the convex hull.
>
> Vincent, after you construct the convex hull, assign it to a Polyhedron_3
> object. You should be able to iterate through the vertices and facets of
> the polyhedron. This is the boundary you want.
>
> Since you mention the points are in 3D, I'm guessing you want the volume
> when you mention "area they are all part of". I don't know if CGAL
> provides the volume of a polyhedron. OTOH if you want the area of the
> boundary, you could sum up the areas of the boundary facets.
>
> ~ash
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