CGAL users discussion list

["Laurent Rineau (CGAL/GeometryFactory)" <>]

On Tuesday, September 10, 2019 8:39:37 PM CEST Renato Poli wrote:
> Hi Sebastien,
> 
> I worked the past days on simplifying my problem and trying to understand
> what is going on.
> I made a very raw code (below) as an example.
> 
> Please find attached three pictures:
> (1) the mesh without refinement
> <http://cgal-discuss.949826.n4.nabble.com/file/t376144/cgal-mesh1.png>
> 
> (2) the refined mesh after
> / typedef CGAL::Delaunay_mesh_size_criteria_2<CDT> Criteria;
>      CGAL::refine_Delaunay_mesh_2(cdt,seeds.begin(), seeds.end(),
> Criteria(0, 100));/
> <http://cgal-discuss.949826.n4.nabble.com/file/t376144/cgal-mesh2.png>
> 
> (3) the seed location (the extra point when compared to mesh1)
> <http://cgal-discuss.949826.n4.nabble.com/file/t376144/cgal-mesh3.png>
> 
> I dont understand
>      (i) why the refiner changes the mesh beyond the shape and size
> criteria? ; and

Hi Renato,

Even without any mesh criteria on faces, the algorithm starts by inserting 
points on constrained edges to ensures that all sub-edges have the Gabriel 
property (empty circumscribed circle).

>      (ii) why the mesh refiner changes the area with a seed?
> 
> Is there any way to avoid those points and get more 'control' on the
> meshing?

The seeds control insertion of points inside the regions, and not on the 
border of it.

There is an undocumented header file in CGAL:

  <CGAL/Delaunay_mesher_no_edge_refinement_2.h> 

It has a function `refine_Delaunay_mesh_2_without_edge_refinement` that you 
could use to mesh the region without touching at all at the constrained 
edges. 
That might suit your needs.


Best regards,

Laurent

-- 
Laurent Rineau, PhD
R&D Engineer at GeometryFactory           http://www.geometryfactory.com/
Release Manager of the CGAL Project       http://www.cgal.org/