How can I get the index of cell

[BBBBBbruce]

Hi, I am using CGAL to do a Delauney Tetrahedralisation, and trying to find the tetrehadron index of the tet contains a query point. How can I quickly get the Tetrahedron index using a Cell_Handle?, The only method I can think of is to use an iterator and a counter. but that means I need to do a search every time I am querying, which is very inefficient. Creating a hash table is not support for Tetrahedron nor Cell.

Thank you for the help.

an example code:

typedef CGAL::Exact_predicates_inexact_constructions_kernel K;
typedef CGAL::Delaunay_triangulation_3<K> Delaunay;
typedef K::Point_3 Point;
typedef Delaunay::Tetrahedron Tet;
typedef Delaunay::Cell_handle Cell_handle;

std::vector<Point> points;
Delaunay T(points.begin(), points.end());
Point queryPoint;
Cell_handle queryPointHandle = T.locate(Point);

// my naive method:
int queryTetIdx = 0;
Tet queryTet = Tet.tetrahedron(queryPointHandle);

for (Delaunay::Finite_cells_iterator it = Tet.finite_cells_begin(); it != Tet.finite_cells_end(); ++it) {
    Tet CurrentTet = T.tetrahedron(it);   

    if(CurrentTet == queryTet) {
        break;
    }else {
        ++queryTetIdx;
    }
}

[MaelRL]

You could use https://doc.cgal.org/latest/Triangulation_3/classCGAL_1_1Triangulation__cell__base__with__info__3.html as cell base and store a unique IDs

typedef Triangulation_data_structure_3<
                         Triangulation_vertex_base_3<K>,
                         Delaunay_triangulation_cell_base_3<
                           K, Triangulation_cell_base_with_info_3<unsigned int, K> >
typedef CGAL::Delaunay_triangulation_3<K, TDS> Delaunay;

[...]
Delaunay T(points.begin(), points.end());
for (Delaunay::Finite_cells_iterator it = Tet.finite_cells_begin(); it != Tet.finite_cells_end(); ++it) {
  Cell_handle c = it;
  c->info() = ...;   // set up unique ID
}

[...]

Cell_handle queryPointHandle = T.locate(Point);
unsigned int cell_id = queryPointHandle->info();

If your triangulation is often modified and the cell IDs would be difficult to maintain manually, there is an undocumented tool called timestamps; see for example the cell base Cell_base_with_timestamp, and it'll set time-based unique IDs for cells automatically. Set it up similarly:

typedef Triangulation_data_structure_3<
                         Triangulation_vertex_base_3<K>,
                         Cell_base_with_timestamp<Delaunay_triangulation_cell_base_3<K> >

[...]

for (Delaunay::Finite_cells_iterator it = Tet.finite_cells_begin(); it != Tet.finite_cells_end(); ++it) {
   Cell_handle c = it;
   std::size_t t = c->time_stamp(); // get unique ID
}

[BBBBBbruce]

Thank you so much! This is exactly what I am looking for

For future reference, the Typedef works for me is, which is what Mael showed me, just break down to several lines.

typedef CGAL::Exact_predicates_inexact_constructions_kernel K;
typedef CGAL::Triangulation_vertex_base_3<K> Vb;
typedef CGAL::Triangulation_cell_base_with_info_3<unsigned int, K> Cb;
typedef CGAL::Triangulation_data_structure_3<Vb, Cb> TDS;
typedef CGAL::Delaunay_triangulation_3<K, TDS> Delaunay;