CGAL users discussion list

[Guillaume Damiand <>]

Hi,


Le 04/06/2014 12:23, Pranav a écrit :
> I want to create a tetrahedral mesh which can have hole/cavity inside it(at
> intermediate stages of computation in an algorithm). For this I am trying to
> use  Linear cell complex(LCC)
> <http://doc.cgal.org/latest/Linear_cell_complex/index.html>  :
>
> I want to perform the following:
> 1. Compute intersection between a triangle and all tetrahedrons in LCC.
> 2. Remove all intersecting tetrahedrons from LCC.(which forms a cavity)
> 3. Replace them with another set of tetrahedrons.(these must be exactly
> aligned with the cavity boundary, to completely fill the hole)
>
> *For task 1:*
> I need to traverse through all tetrahedrons. I do not find any iterator sort
> of functionality for LCC. Do I need to use a standard graph traversal
> algorithm over /beta_3/ links of darts to traverse all tetrahedrons?

Do you need a specific order ? If not you can use 
One_dart_per_cell_range<3> range [1] which give you one dart per each 
volume (3-cell) of the lcc.


> *For Task 2:*
> Here, I think /remove_cell()/ function has to be used to remove the
> intersecting 3-cells.

Yes.
Be-careful, you cannot use remove_cell during the 
One_dart_per_cell_range<3> range; you need to store in an external DS 
(for example a std::vector) the darts to remove, and in a second loop 
through this ds call the remove_cell<3> function.

> *For Task 3:*
> Although, I do find /make_tetrahedron()/ function that can be used to add a
> new tetrahedron into LCC, but can it assure that these new tetrahedrons are
> exactly aligned with the boundary of previously created cavity?


The main question here is how do you compute the set of tetrahedra 
required to fill the cavities ? (which could be a difficult problem...)

If you are able to compute these sets, and if they have the good 
geometry (i.e. the boundaries of the sets fill the cavities), you can 
call the undocumented method sew3_same_facets which will do the job 
(i.e. identify all the pairs of faces having the same geometry).

Regards
Guillaume

[1] 
http://doc.cgal.org/latest/Combinatorial_map/classCombinatorialMap.html#a5bf899ddc01ff5ae5ab10929cdd0086b



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Guillaume DAMIAND

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