CGAL users discussion list

[Philipp Moeller <>]

Nuno Pessanha Santos 
<>
 writes:

> Thanks Sebastien.
> For my implementation every millisecond counts, I have to implement that in 
> the first way suggested by Sebastien.
> Another question,I hope the final one.
> When I make:
> CGAL::convex_hull_3(points.begin(), points.end(), 
> poly);std::vector<Point_3> chull_points(poly.points_begin(), 
> poly.points_end());
> It´s not suppose to access the point 0 coordinate X by the:std::cout << 
> chull_points[0].x;
> This gives me the error:
> "error C3867: 'CGAL::Point_3<R_>::x': function call missing argument list; 
> use '&CGAL::Point_3<R_>::x' to create a pointer to member"

x is a member function. You need to actually call it to get x,
e.g. chull_points[0].x().

To get the behavior of indices you could extend the Point primitive of
the kernel and add an index to it. That index would be preserved in the
points of the Polyhedron, but this is rather tricky and I would only
recommend trying it if you really need the speed.

>
>> Date: Thu, 24 Oct 2013 16:51:32 +0200
>> From: 
>> 
>> To: 
>> 
>> Subject: Re: [cgal-discuss] Convex_hull_3 - CGAL
>> 
>> The only way to do it for now I think is to use the Delaunay
>> triangulation.
>> Note that it will take more time to compute than the other function.
>> (I'll add a todo for adding this in a future release)
>> 
>> Build the triangulation following this example:
>> http://doc.cgal.org/latest/Triangulation_3/index.html#Triangulation_3UsingtheBoostTransformIterator
>> 
>> Then something like this should work (not tested):
>> 
>> struct Chull_indices
>> {
>>    void operator()(Delaunay::Vertex_handle vh) const
>>    {
>>        m_indices.push_back(vh->info());
>>    }
>> 
>>    std::vector<std::size_t> m_indices;
>> };
>> 
>> Chull_indices chull_indices;
>> 
>> T.adjacent_vertices(T.infinite_vertex(),
>>                      boost::make_function_output_iterator(chull_indices)
>> );
>> 
>> for( std::size_t i : chull_indices.m_indices)
>>    std::cout << i << std::endl;
>> 
>> Sebastien.
>> 
>> On 10/24/2013 04:12 PM, Nuno Pessanha Santos wrote:
>> > Hi,
>> >
>> > Thanks Sebastien for your  answer.
>> >
>> > I only need the index of the points, example:
>> >
>> > Original Point Cloud:
>> > point 1
>> > point 2
>> > point 3
>> > point 4
>> >
>> > Convex Hull:
>> > point 3
>> > point 4
>> >
>> > I want to read the 3 and 4, to make them correspond in my further
>> > processing.
>> >
>> > Thanks.
>> >
>> > Nuno Pessanha Santos
>> >
>> >
>> >
>> >
>> >  > Date: Thu, 24 Oct 2013 07:11:37 +0200
>> >  > From: 
>> > 
>> >  > To: 
>> > 
>> >  > Subject: Re: [cgal-discuss] Convex_hull_3 - CGAL
>> >  >
>> >  > On 10/24/2013 05:31 AM, Nuno Pessanha Santos wrote:
>> >  > > Hi,
>> >  > >
>> >  > > I am starting to use CGAL, and maybe this is a stupid question but I
>> >  > > need some help.
>> >  > >
>> >  > > When you use the function "CGAL::convex_hull_3(points.begin(),
>> >  > > points.end(), Polyhedron_3 poly);" you obtain the polyhedron poly.
>> >  > >
>> >  > > How can I read the obtained vertices or the points index that are
>> >  > > contained in the convex hull? I see so many examples but none of 
>> > them
>> >  > > could help me in my task.
>> >  >
>> >  > Is the following what you are looking for?
>> >  >
>> >  > Polyhedron_3 poly;
>> >  > CGAL::convex_hull_3(points.begin(), points.end(), poly);
>> >  > std::vector<Point_3> chull_points(poly.points_begin(),
>> > poly.points_end());
>> >  >
>> >  >
>> >  > Sebastien
>> >  >
>> >  > >
>> >  > > Thanks
>> >  > >
>> >  > > Nuno Pessanha Santos
>> >  > >
>> >  > >
>> >  >
>> >  >
>> >  > --
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>> >  >
>> >  >
>> 
>> 
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>> 

-- 
Philipp Moeller 
GeometryFactory