CGAL users discussion list

[Daniel Duque <>]

On Monday 30 January 2012 16:07:18 Adam Hopkins wrote:
> Hi Daniel and Sebastien:
> 
> Again, thank you for your answers. When I say external vertexes, I am
> refering to all vertexes in external faces, is to say: using the example
> code of my first email, I can compute the external cells of a
> triangulation, and each of them has an external face defined for three
> vertexes, which are the external vertexes.

Hi,

That's right: unless I am very wrong, one vertex is the infinite one and the 
other two belong to the convex hull...

Best,

Daniel


> 
> For example assume that I have a triangulation of a sphere, I want to know
> which are the vertexes in the external surface. Please, see the code in my
> first email for more references.
> 
> thank in advance and waiting suggestions
> A.
> 
> On Mon, Jan 30, 2012 at 3:58 PM, Sebastien Loriot (GeometryFactory) <
> 
> >
>  wrote:
> > What is your definition of external vertices?
> > 
> > Sebastien.
> > 
> > On 01/30/2012 03:41 PM, Adam Hopkins wrote:
> >> Hi Daniel:
> >> 
> >> Thank you for your help, but I think that it is not the correct way to
> >> solve my problem. When the convex hull is computed not all the external
> >> vertexes are included. For this reason, I need other form to know which
> >> are the real external vertexes of a triangulation.
> >> 
> >> Regards and waiting more suggestions
> >> A.
> >> 
> >> On Mon, Jan 30, 2012 at 3:29 PM, Daniel Duque 
> >> <
> >> 
> >> <mailto:>>
> >>  wrote:
> >>    On Monday 30 January 2012 15:20:52 Adam Hopkins wrote:
> >>     > Hi all,
> >>     > 
> >>     > Thank you for your previous answers, but I have a last issue
> >>    
> >>    related with
> >>    
> >>     > triangulations.
> >>     > 
> >>     > Using the example code below, I can know which are the external
> >>    
> >>    cells of a
> >>    
> >>     > triangulations, but I also need to know which are the external
> >>    
> >>    vertex of
> >>    
> >>     > the same triangulation.
> >>    
> >>    I guess you mean the vertices that form the convex hull. Have a look
> >>    here:
> >>    
> >>    http://www.cgal.org/Manual/**latest/doc_html/cgal_manual/**
> >> 
> >> Triangulation_2/Chapter_main.**html#Subsection_36.4.2<http://www.cgal.or
> >> g/Manual/latest/doc_html/cgal_manual/Triangulation_2/Chapter_main.html#S
> >> ubsection_36.4.2>
> >> 
> >>    Best,
> >>    
> >>    Daniel
> >>    
> >>     > Is there any form to know which are the external
> >>     > facets of each of these cells in order to know which are the most
> >>    
> >>    external
> >>    
> >>     > vertexes of this triangulation?
> >>     > 
> >>     > Concretely, How Can I know which are the external vertices of a
> >>     > triangulation?
> >>     > 
> >>     > std::vector<Cell_handle> infinite_cells;
> >>     > T.incident_cells(T.infinite_**vertex(),
> >>    
> >>    std::back_inserter(infinite_**cells));
> >>    
> >>     > for(int ii = 0; ii < (int)infinite_cells.size(); ii++)
> >>     > {
> >>     > Cell_handle c = infinite_cells[ii];
> >>     > Cell_handle e = c->neighbor(c->index(T.**infinite_vertex()));
> >>     > }
> >>     > 
> >>     > Regards and thank you for all
> >>     > A.
> >>    
> >>    --
> >>    http://dcain.etsin.upm.es/~**daniel<http://dcain.etsin.upm.es/~daniel
> >>    >
> >>    
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