CGAL users discussion list

[Manuel Caroli <>]

Hi Juliano,

Juliano Costa wrote:
> Hello again Manuel,
>  
> Yes. By "surface" I was refearring to the convex hull (the outter side 
> of the envelop points).
Note that you can use

incident_cells(infinite_vertex(), output_iterator) to get the cells that 
have the triangles of the convex hull as a facet.
>  
> This new package for "Surface reconstruction" seems just GREAT.
> It looks exactlly what I need to do.
> I'm going to download the beta version to test it now!
>  
> Just one more thing:
> I was trying to to integrate the alpha shape with my current example.
> Right now I have CGAL::Triangulation_vertex_base_with_info_3 in order to 
> set the ->info() with my
> index.
>  
> For the alpha shape, If I really understood it, I must use 
> CGAL::Alpha_shape_vertex_base_3 but this does not contain
> the "info" field.
> Is there any other way for me to set the "info"?
> There should be an CGAL::Alpha_shape_vertex_base_with_info_3 file to do 
> so, right?!
It should be possible to use them in a nested way, i.e.
Alpha_shape_vertex_base_3<Traits,Triangulation_vertex_base_with_info_3>

Maybe with the above mentioned approach to extract the convex hull you 
don't need the info anymore...

best

Manuel

>  
> Thanks a lot again,
>  
> Best regards,
>  
> Juliano.
>
>  
> 2009/8/5 Manuel Caroli < 
> <mailto:>>
>
>     Hi Juliano,
>
>     Juliano Costa wrote:
>
>         Hello Manuel,
>          
>
>     [...]
>     The *interior* of the (smallest) sphere passing through the two
>     vertices of the diagonal of a cube (or cuboid) does not contain any
>     other vertices of the cube (or cuboid). This is a degenerate case
>     though. The CGAL::Triangulation_3 partitions the convex hull of the
>     point set into tetrahedra even in degenerate cases. So the result
>     you get is fine.
>
>          Well, I ignored this issue and proceed with my intend so I used
>         the DelaunayTriangleHierarchy::Finite_facets_iterator like this:
>
>     I don't actually get what you mean by "surface" in the code below.
>     Are you talking about the convex hull?
>
>
>          //On inserting points I'm setting the Vertex_hanlde->info with
>         an "unsigned long" value as index.  //I need to get the
>         triangles points indexes:
>         CPUInt64_t  _indexA,_indexB,_indexC;
>         CPUInt64_t* _iPointsIndexes[3];
>         _iPointsIndexes[0] = &_indexA;
>         _iPointsIndexes[1] = &_indexB;
>         _iPointsIndexes[2] = &_indexC;
>          //having DelaunayTriangleHierarchy _delaunayTrianguleHierarchy;
>         DelaunayTriangleHierarchy::Finite_facets_iterator _fit =
>         _delaunayTriangule.finite_facets_begin();  while(_fit !=
>          _delaunayTriangule.finite_facets_end())
>         {
>             //typedef CGAL::Delaunay_triangulation_3<K,Tds>
>         DelaunayTriangle;
>             DelaunayTriangle::Facet  _facet = *_fIt;
>             unsigned long _facetIndex = _facet.second;
>               //typedef DelaunayTriangle::Cell_handle CGALCellHandle;
>             CGALCellHandle facetCell = _facet.first;
>             char _isInfiniteCell =
>         _delaunayTriangule->is_infinite(_facetCell);
>             //neighbor cell
>             CGALCellHandle neigborCell = _cell->neighbor(_facetIndex );
>             char _isInfiniteNeigbor =
>         _delaunayTriangule.is_infinite(neigborCell);
>               if( (!_isInfiniteCell) && (!isInfiniteNeigbor) )
>             {
>                  //I only want the surface right?!?!!
>                  continue;
>             }     char _iTriVrr=0;
>                 for(char _iPointsLoop=0;_iPointsLoop<4;_iPointsLoop++)
>             {
>                   if( _iPointsLoop != _facetIndex )
>                   {
>                       *_iPointsIndexes[_iTriVrr++] = (unsigned
>         long)(_fIt->first->vertex(_iPointsLoop)->info());
>                   }
>             }
>             //Here I got _indexA,_indexB,_indexC which I'm saving on the
>         OBJ file.
>              _fit++;
>         }  With this code, when I provide an ordinary box or even a
>         sphere the result is just wonderful.
>         But when I try this with a small points cloud (10000 3d points
>         of a tunnel for example) the result is a mess.
>         I got triangles coming from a side to the another and from the
>         top to the ground.
>         I want just the surface.
>          I used this tunnel points cloud as example, but my intention is
>         to use the same algorith providing points cloud of any
>         3d object or place  (e.g.: an office room).
>          Now I was about to try to integrate the my current source code
>         with the CGAL "alpha shape" example...
>          But you've come with a different "light": "use a surface
>         mesher". But a surface mesher wouldn't interpolate "new created
>         points"?
>
>     Yes the surface mesher creates its own points so it does not seem
>     adapted to your problem.
>
>         So, to make this "surface mesher" what I've be doing so far is
>         useless?
>
>         On the CGAL examples for surface mesher  (like
>         examples/Surface_mesher/mesh_an_implicit_function.cpp)
>         
> <http://www.cgal.org/Manual/3.3/examples/Surface_mesher/mesh_an_implicit_function.cpp>the
>         input points comes from a generator surface function  //
>         defining the surface
>         //  Surface_3
>         
> <http://www.cgal.org/Manual/3.3/doc_html/cgal_manual/Surface_mesher_ref/Concept_Surface_3.html#Cross_link_anchor_1083>
>         surface
>
>          Can I insert points of an unknown shape?
>
>     You might want to have a look at the new Surface reconstruction
>     package:
>     
> http://www.cgal.org/Manual/beta/doc_html/cgal_manual/Surface_reconstruction_points_3/Chapter_main.html
>     Note that this is only a beta release. The final release will be
>     available by mid September.
>
>     best
>
>     Manuel
>
>          I really appreciate your help!
>         Thanks once again!
>          Juliano Costa
>         Brazil.
>           2009/8/5 Manuel Caroli 
> <
>         
> <mailto:>
>         
> <mailto:
>         
> <mailto:>>>
>
>
>            Hi Juliano,
>
>            the Triangulation_3 package computes a triangulation of R^3
>         with the
>            input points as vertices. If you want to compute a triangular
>         mesh
>            approximating a surface you should use a surface mesher.
>         Maybe you
>            could be more specific about your problem.
>
>            best
>
>            Manuel
>
>
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