CGAL users discussion list

[Sebastien Loriot <>]

On Wednesday 04 February 2009 11:38:11 am 

 wrote:
> Hi All,
>
> I need to find a particular point from a sample of points of which I made
> convex hull, is on the convex hull or not. I am not finding any particular
> function for it in manual.
>
> Please give right direction, how to do it. I created ch_object of n points,
> now I don't know which points were involved in making the hull and which
> were excluded.
>
> Thanks
> Avanindra

Hello,


From the manual page
http://www.cgal.org/Manual/3.4/doc_html/cgal_manual/Convex_hull_2/Chapter_main.html#Section_11.3
You can find one example of how to construct the convex hull of a set of 
points. Instead of using the standard input and output like in the example, 
you can use lists or another container.
Indeed, following the link behind CGAL::ch_graham_andrew, we can see that the 
third parameter of CGAL::ch_graham_andrew is an OutputIterator which gives 
you the list of points on the convex hull. A simple equality test then solves 
your problem.


Another solution is to use the triangulation_2 and the vertices incident to 
the infinite vertex.


Sebastien.