CGAL users discussion list

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

Le Thursday, June 8, 2017 8:59:46 PM CEST Ignacio Javier Osorio Wallace a ?
crit :
> Hello CGAL community, I need a small help with a surface extraction that
> I need to implement.
> 
> I'm creating a surface for a finite element algorithm. And I need the
> edges to have a minimum size restriction. I would be perfect if the SD
> of all the edges were as small as possible.

Hi,

You cannot define a minimal size for edges (or triangles) when using 
`CGAL::make_surface_mesh`. If the size of edges is significantly smaller than 
the size criterion given to the critera object 
(`CGAL::Surface_mesh_default_criteria_3`), then that probably means that the 
geometry of the domain surface has locally a small feature size.

You may try post-process the result of `CGAL::make_surface_mesh` with a 
surface simplification algorithm: export the `c2t3` object to a polyhedron, 
and then use the methods from the CGAL chapter "Triangulated Surface Mesh 
Simplification":

  http://doc.cgal.org/4.10/Surface_mesh_simplification/index.html

But the global guaranties (no self-intersection) will no longer be 
guaranteed.

> Here is a the code.
> Thx for the help, btw.
> Best regards,
> Ignacio.
> 
> typedef CGAL::Simple_cartesian<double> Kernel;
> typedef Kernel::Point_2 Point_2;
> 
> // default triangulation for Surface_mesher
> typedef CGAL::Surface_mesh_default_triangulation_3 Tr;
> // c2t3
> typedef CGAL::Complex_2_in_triangulation_3<Tr> C2t3;
> typedef Tr::Geom_traits GT;
> 
> typedef CGAL::Gray_level_image_3<GT::FT, GT::Point_3> Gray_level_image;
> typedef CGAL::Implicit_surface_3<GT, Gray_level_image> Surface_3;
> 
> Tr tr;            // 3D-Delaunay triangulation
> C2t3 c2t3 (tr);   // 2D-complex in 3D-Delaunay triangulation
> char *inriaFile;
> char *outputFile;
> 
> Gray_level_image image(inriaFile, 0.3);
> 
> GT::Point_3 bounding_sphere_center(109,109,67);
> 
> GT::FT bounding_sphere_squared_radius = float(218) * float(218) *
> float(2);
> 
> GT::Sphere_3 bounding_sphere(bounding_sphere_center,
> bounding_sphere_squared_radius);
> 
> Surface_3 surface(image, bounding_sphere, 0.00001);
> 
> CGAL::Surface_mesh_default_criteria_3<Tr> criteria(30,2,2);
> 
> CGAL::make_surface_mesh(c2t3, surface, criteria, CGAL::Manifold_tag());
> 
> //for(C2t3::Vertex_iterator iter(c2t3.vertices_begin()); iter !=
> c2t3.vertices_end(); iter++ ) {
> //std::cout << iter->point().x() << iter->point().y() << iter->point()
> << std::endl;
> ////Point p(iter->point());
> //}
> 
> std::ofstream out(outputFile);
> CGAL::output_surface_facets_to_off (out, c2t3);
> std::cout << c2t3.number_of_facets() << std::endl;
> 
> std::cout << "qRx : Surface, final number of points: " <<
> tr.number_of_vertices() << "\n";
> std::cout << "qRx: Surface, end!!" << std::endl;



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