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[Daniel Duque <>]

Thanks Sebastien.

I fact, I do have info on the vertices, e.g the bool variable that marks a vertex as being inner or outer and lots of other stuff. That info gets copied correctly on the new T2 triangulation, but the latter is destroyed when building the alpha shape. My problem is then either to transfer back the info to the original T triangulation (which I do, but in a manner which is not too efficient), or perhaps stopping the alpha shape constructor from destroying my triangulation.

I have just noticed there is another way to create an alpha shape, from a list of points:

http://doc.cgal.org/latest/Alpha_shapes_2/classCGAL_1_1Alpha__shape__2.html#a5524e49e27ef267165673d0a36bddb14

If I could make an alpha shape from a list of pair< points, vertex handle >, I guess I could retrieve the vertex from which each of the points came from...

Best,

Daniel

 

On Mon, Jul 27, 2015 at 1:28 AM, Sebastien Loriot (GeometryFactory) <> wrote:

What about adding an info in the vertex type?

See this example:
http://doc.cgal.org/latest/Triangulation_2/index.html#title40
using this class:
http://doc.cgal.org/latest/Triangulation_2/classCGAL_1_1Triangulation__vertex__base__with__info__2.html

Sebastien.

On 07/24/2015 05:40 PM, Daniel Duque wrote:

Hello everyone.

I have been using alpha shapes to identify the outer vertices of
triangulations
for some time, and I am very happy with the method. However, the
underlying triangulation
is destroyed in the process. This often OK, but can be inconvenient if
one just wants to "mark"
the nodes as outer, but keeping the triangulation. Right now I am doing
this crude treatment
which, as you see, copies the triangulation, destroys it, then marks the
vertices on the original
triangulation as outer if the coincide with the nodes of the alpha shape.

The crudest part, as you can see, is that this coincidence is
implemented by "locate", since
I have lost any other connection with the original triangulation. I
guess I could hack the
copy procedure in order to include a pointer or handle to the original
one...

Any ideas will be welcome.

Best,

Daniel Duque
UPM

// T is a global Delaunay triangulation

void surf_detect(void) {

   Triangulation T2(T);

   FT hh= 1.2 * simu.h();

   FT alpha=hh*hh;
   Alpha_shape_2 al( T2, alpha );

   for (Alpha_shape_vertices_iterator asv=al.alpha_shape_vertices_begin();
        asv!=al.alpha_shape_vertices_end();
        ++asv) {

     Point p=(*asv)->point();

//  mark vertices in the alpha shape as boundary vertices
//  implemented by locate (not very efficient, I guess)

     int i;
     Triangulation::Locate_type lt;
     Face_handle fc=T.locate(p, lt , i );
     fc->vertex(i)->boundary.set( true );
   }

   return;
}

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