CGAL users discussion list

[Pratyush Pranav <>]

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 <> 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 <> 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 <> wrote:

On 11 Apr 2016, at 16:06, Pratyush Pranav <> 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