CGAL users discussion list

["Sebastien Loriot (GeometryFactory)" <>]

I jump late in the discuss and did not read the full thread so I might
be wrong but it seems you reimplemented the function
convex_hull_3_to_polyhedron_3.

http://doc.cgal.org/latest/Convex_hull_3/group__PkgConvexHull3Functions.html#gaa87070e950e63e3a7395a2fb14c7ea7c


Sebastien.

On 04/14/2016 10:10 AM, Pratyush Pranav wrote:
> no, i finally convert to convex hull from triangulation, because when i
> visualised the triangulation, it was not what i had thought it was
> (attaching a visualisation of the triangulation of the point, as well as
> the extracted convex hull (which was what i am after). the triangulation
> doesn’t even look alright to me ( i output all the finite vertices,
> edges and facets in off format)…however, the convex hull comes out just
> alright. it is clear that not all the simplifies of the triangulation
> are a part of the convex hull, so just taking the simplifies incident to
> the infinite vertex or cells in the triangulation and think it give the
> full convex hull was a wrong idea…i was getting bad results then. by the
> way, is it true that a simplex that belongs to convex hull may actually
> not be a part of the triangulation?
>
> also, more importantly, when i output the infinite vertex it gives me
> the coordinates as (0,0,0). i faintly remember reading in the coal
> manuals that for points on sphere, there is an insertion of a dummy
> point at (0,0,0)…just trying to confirm. if this is true, i can
> partially make sense of the garbage result i was getting.
>
> so now, i convert to convex hull, and write it to a polyhedron_3. by the
> way, i think i have my answer. the halfedges are unique to a facet from
> what it looks like on the polyhedron documentation.
>
> pratyush
>
>
> > On 14 Apr 2016, at 09:00, Monique Teillaud 
> > <
> > <mailto:>>
> >  wrote:
> >
> > Hard to answer, without knowing which precise package you are finally
> > using.
> > If it is 3D triangulation, then:
> > http://doc.cgal.org/latest/Triangulation_3/classCGAL_1_1Triangulation__3.html#a46150602a4dd3953bfc820c7eebf123d
> > but there are no half edges and no handles to facets...
> >
> > --
> > Monique Teillaud
> > http://www.loria.fr/~teillaud/
> > INRIA Nancy - Grand Est, LORIA
> > Institut National de Recherche en Informatique et Automatique
> >
> > On 13 Apr 2016, at 23:12, Pratyush Pranav 
> > <
> > <mailto:>>
> >  wrote:
> >
> > > i have been doing something and getting somewhere…working with the
> > > triangulation did not give me the right thing…so i switched over to
> > > the convex hull computed from the triangulation. i have one more
> > > question though.
> > >
> > > is there a way to extract the incident facets on a vertex?
> > >
> > > am i right if i say that i find the incident half edge to a vertex,
> > > from that half edge get a handle to the incident facet? does every
> > > half edge have a unique facet that it points to?
> > >
> > > given a half edge handle, what is the proper way to extract the
> > > incident facet handle to it?
> > >
> > > > On 11 Apr 2016, at 20:29, Monique Teillaud
> > > > <
> > > >  
> > > > <mailto:>>
> > > >  wrote:
> > > >
> > > > On 11 Apr 2016, at 16:06, Pratyush Pranav 
> > > > <
> > > > <mailto:>>
> > > >  wrote:
> > > >
> > > > > yes i get it a bit…been playing around with things for a while…but
> > > > > now stuck a bit at the proper usage of circulators.
> > > > >
> > > > > my problem is the following :
> > > > >
> > > > > first i want to iterate over all the incident edges to a vertex.
> > > > > then for each edge i want to determine if it is on the convex hull.
> > > > > for this, I want to circulate over all the incident cells of an
> > > > > edge to determine if the edge is on the boundary of the hull (if
> > > > > one or more cells incident to the edge are infinite cells, the edge
> > > > > is on the hull).
> > > > >
> > > > > how to do this? as i gather circulators do not behave in the same
> > > > > fashion as iterators.
> > > >
> > > > it is roughly the same, except that there is no range associated.
> > > >
> > > > > i was reading on circulators, and saw that i could convert a
> > > > > circulator to a container and iterate over the contents of the
> > > > > container so i define it as follows
> > > >
> > > > this looks uselessly complicated
> > > > why not just use the circulator in the simplest possible way, as in
> > > > the example given here
> > > > http://doc.cgal.org/latest/Circulator/index.html#title3 ?
> > > > there must also be an example in some triangulation chapter (if not
> > > > 3d, then 2d)
> > > >
> > > > --
> > > > Monique Teillaud
> > > > http://www.loria.fr/~teillaud/
> > > > INRIA Nancy - Grand Est, LORIA
> > > > Institut National de Recherche en Informatique et Automatique