CGAL users discussion list

[Manuel Caroli <>]

Hui DING wrote:
> Thanks, but yes, I've already seen that, I am just wondering what every 
> number stands for. for example: 5 1 3 6, I cant see what do they mean(I 
> hope maybe I could understand this chapiter more and quicker if I know 
> those numbers )?
Vertices and cells are indexed. These numbers determine the cell/vertex 
in question, see below:

11            - the number of cells
5 1 3 6     - Cell containing vertex 5, 1, 3 and 6. (note that the order 
matters)
1 2 3 4     - ?
2 0 3 4     - ?
2 1 0 4     - ?
1 3 2 0     - ?
0 1 3 5     - ?
6 1 3 4     - ?
0 5 3 4     - ?
0 1 5 4     - ?
5 1 6 4     - ?
5 6 3 4     - last cell (11 cells as written above)
6 10 9 5     - This is the neigboring relation. The 1st cell (cell 0) 
has the cells 6, 10, 9, and 5 as neighbors.
2 6 3 4     - ?
7 1 3 4     - ?
8 2 1 4     - ?
2 3 5 1     - ?
0 7 8 4     - ?
1 10 9 0     - ?
10 2 8 5     - ?
9 7 3 5     - ?
6 10 8 0     - ?
6 7 9 0     - ?
> And also another question, does the number of cells change? so for one 
> same 3D object, the triangulation changes everytime when we re-construct 
> it?
If you are computing a Delaunay or regular Triangulation of a 
non-degenerate point set, then this is uniquely defined. Therefore the 
resulting triangulation is always the same. Even if the point set is 
degenerate CGAL gives you always the same triangulation.
If you are not computing a Delaunay or regualar triangulation then it 
depends on the order in which you insert the points.

Note that the indices as written above can change of course.

Best

Manuel