CGAL users discussion list

[Burak ER <>]

Hi Sebastien,

I am now having difficulties with the space filling tetrahedrons. They
are too small[1] when compared to other tetrahedrons. How can I prevent
this behavior? 

Sorry for these newbie questions.

Thank you.

Burak

[1]http://s10.postimg.org/rblr196hl/Screenshot_from_2013_10_25_17_40_10.png

Cum, 2013-10-25 tarihinde 16:13 +0300 saatinde, Burak ER yazdı:
> Thank you,
> 
> This solved my problem.
> 
> Burak ER
> 
> Cum, 2013-10-25 tarihinde 12:03 +0200 saatinde, Sebastien Loriot
> (GeometryFactory) yazdı:
> > You need to protect the edges of your box.
> > 
> > One solution is to do like this example:
> > http://doc.cgal.org/latest/Mesh_3/index.html#Mesh_3MeshingDomainswithSharpFeatures
> > 
> > or to protect them by hand.
> > 
> > Sebastien.
> > 
> > On 10/25/2013 11:20 AM, Burak ER wrote:
> > > Sorry for the not working link. You can find it here.
> > > <http://s16.postimg.org/pv4ehn3et/Screenshot_from_2013_10_25_12_17_21.png>
> > >
> > > Cum, 2013-10-25 tarihinde 12:14 +0300 saatinde, Burak ER yazdı:
> > >> Dear Sebastian,
> > >>
> > >> This may not be a minimal example. I have created a python interface
> > >> for my application. Within this interface I divide the off file into
> > >> tetrahedrons with CGAL c++ api on the background. I use this
> > >> generation code on the c++ side;
> > >>
> > >> #include <CGAL/Exact_predicates_inexact_constructions_kernel.h>
> > >> #include <CGAL/Mesh_triangulation_3.h>
> > >> #include <CGAL/Mesh_complex_3_in_triangulation_3.h>
> > >> #include <CGAL/Mesh_criteria_3.h>
> > >> #include <CGAL/Polyhedral_mesh_domain_3.h>
> > >> #include <CGAL/make_mesh_3.h>
> > >> #include <CGAL/refine_mesh_3.h>
> > >> #include <iostream>
> > >> // IO
> > >> #include <CGAL/IO/Polyhedron_iostream.h>
> > >>
> > >> // Domain
> > >> typedef CGAL::Exact_predicates_inexact_constructions_kernel K;
> > >> typedef CGAL::Polyhedron_3<K> Polyhedron;
> > >> typedef CGAL::Polyhedral_mesh_domain_3<Polyhedron, K> Mesh_domain;
> > >>
> > >> // Triangulation
> > >> typedef CGAL::Mesh_triangulation_3<Mesh_domain>::type Tr;
> > >> typedef CGAL::Mesh_complex_3_in_triangulation_3<Tr> C3t3;
> > >>
> > >> // Criteria
> > >> typedef CGAL::Mesh_criteria_3<Tr> Mesh_criteria;
> > >>
> > >> // To avoid verbose function and named parameters call
> > >> using namespace CGAL::parameters;
> > >>
> > >> class MeshElement;
> > >>
> > >> void Mesh(void)
> > >> {
> > >>
> > >>   boost::filesystem::path mypath(filename);
> > >>   std::ifstream input(filename.data());
> > >>
> > >>   if(mypath.extension()!=boost::filesystem::path(".off")){
> > >>   std::string errormessage ="Invalid extension is specified with the
> > >> mesh file";
> > >>   throw std::invalid_argument(errormessage);
> > >>   }
> > >>
> > >>   // Create input polyhedron
> > >>   Polyhedron polyhedron;
> > >>
> > >>   input >> polyhedron;
> > >>
> > >>   // Create domain
> > >>   Mesh_domain domain(polyhedron);
> > >>
> > >>   // Mesh criteria (no cell_size set)
> > >>   Mesh_criteria criteria(facet_angle, facet_size,
> > >> facet_distance,/*facet_topology*/
> > >>                          cell_radius_edge_ratio, cell_size);
> > >>
> > >>   // Mesh generation
> > >>   c3t3.clear();
> > >>
> > >>   c3t3 = CGAL::make_mesh_3<C3t3>(domain, criteria, no_perturb(),
> > >> no_exude());
> > >>
> > >>   elems.clear();// clear our vector
> > >>
> > >>   interfacingpairs.clear();
> > >>
> > >>   handlemap.clear();
> > >>
> > >>   elems.resize(c3t3.number_of_cells_in_complex()); // resize it as the
> > >> new number of elements
> > >>
> > >>   size_t i=0;
> > >>   /*
> > >>    * This is not a nice way to index elements
> > >>    * we could use cell_with_info structure of cgal but really how to
> > >> use that? No tutorial, no example at all on its document!!!
> > >>    *
> > >>    * */
> > >>   for(C3t3::Cells_in_complex_iterator
> > >> it=c3t3.cells_begin();it!=c3t3.cells_end();it++){
> > >>
> > >>   //Create new elements
> > >>
> > >>   //share_ptr handles deletion of the newly created element
> > >>   elems[i]=shared_ptr<MeshElement>(new Linear4NodeTetMeshElem(it));
> > >>
> > >>   //Give an index to handle
> > >>   handlemap[it]=i;
> > >>   i++;
> > >>   }
> > >>   // Add interactions
> > >>   for(C3t3::Cells_in_complex_iterator
> > >> it=c3t3.cells_begin();it!=c3t3.cells_end();it++){
> > >>
> > >>             //For each neighbor of the currrent iterator
> > >> for(int j=0;j<4;j++)
> > >>         {
> > >>
> > >>      C3t3::Cell_handle neigh=it->neighbor(j);
> > >>
> > >> /*Check if we have this neighbor handle*/
> > >> if(c3t3.is_in_complex(neigh))
> > >> {
> > >> size_t indexel=handlemap[it];
> > >> size_t indexneigh=handlemap[neigh];
> > >>
> > >> //Get element and its neighbors from element list
> > >> shared_ptr<MeshElement> el;
> > >> shared_ptr<MeshElement> neighel;
> > >>        //Change the ordering of the elements
> > >>         if(indexel<indexneigh){
> > >> el=elems[indexel];
> > >> neighel=elems[indexneigh];}
> > >>          else{
> > >> neighel=elems[indexel];
> > >>         el=elems[indexneigh];
> > >> }
> > >>
> > >>
> > >> nodePairsIndices indiceofpairs;
> > >>
> > >> //Get shared node list
> > >> indiceofpairs=getNodeCon(el,neighel);
> > >>
> > >>        //check if there is a face share
> > >>          if(indiceofpairs.size()>=3)
> > >> {
> > >> //Create the pair
> > >> ElementPair pair(el,neighel,indiceofpairs);
> > >>
> > >> //Add it into the interfacing pair list
> > >>         if(!interfacingpairs[pair])
> > >> {
> > >>
> > >> interfacingpairs[pair]=shared_ptr<ElementPair>(new
> > >> ElementPair(el,neighel,indiceofpairs));
> > >>
> > >> }
> > >> }
> > >>   }
> > >>                   }
> > >>
> > >> }
> > >>   std::cout<<"Meshing is complete "<<std::endl;
> > >>   std::cout<<"Number of tetrahedral elements 
> > >> "<<elems.size()<<std::endl;
> > >>   std::cout<<"Number of interaction elements
> > >> "<<interfacingpairs.size()<<std::endl;
> > >> }
> > >>
> > >> Using this function and the  off file in the attachment;
> > >>
> > >> When I use the parameters as
> > >> facet_angle=33,
> > >> facet_distance=.6,
> > >> facet_size=0.6,
> > >> cell_radius_edge_ratio=0.11,
> > >> cell_size=1e-3
> > >>
> > >> The result is 5580 elements and they are distributed as here <http://>
> > >> where you can see the empty parts on the boundary of the plate.
> > >>
> > >> Also slight change on the cell_radius_edge_ratio=0.15 makes it even
> > >> worser as here.
> > >> <http://s14.postimg.org/o8j6yl07l/Screenshot_from_2013_10_25_12_08_06.png>
> > >>
> > >> What do you think the problem is?
> > >>
> > >> Burak
> > >>
> > >> Cum, 2013-10-25 tarihinde 09:28 +0200 saatinde, Sebastien Loriot
> > >> (GeometryFactory) yazdı:
> > >>> It might help if you share a minimal example showing the pb.
> > >>>
> > >>> Sebastien.
> > >>>
> > >>> On 10/25/2013 09:26 AM, Burak ER wrote:
> > >>> > Dear Cgal Users,
> > >>> >
> > >>> > I really need help on this problem. Still waiting for an answer.
> > >>> >
> > >>> > Thank you in advance.
> > >>> >
> > >>> > Burak ER
> > >>> >
> > >>> > Pzt, 2013-10-21 tarihinde 18:40 +0300 saatinde, Burak ER yazdı:
> > >>> >> Dear Cgal Users,
> > >>> >>
> > >>> >> I am trying to mesh a rectengular prism domain from an off file 
> > >>> >> into
> > >>> >> tetrahedral elements using cgal. But whatever parameters I use 
> > >>> >> within
> > >>> >> criteria structure, I get a mesh where the boundaries are not 
> > >>> >> conserved
> > >>> >> rather they are "uneven".
> > >>> >>
> > >>> >> What may cause that? How to force keeping boundaries exact while
> > >>> >> meshing?
> > >>> >>
> > >>> >> Thank you in advance.
> > >>> >>
> > >>> >> --
> > >>> >> Burak ER
> > >>> >>
> > >>> >> Research Assistant
> > >>> >> Mechanical Engineering Department
> > >>> >> Bursa Technical University
> > >>> >>
> > >>> >>
> > >>> >>
> > >>> >
> > >>>
> > >>>
> > >>
> > >>
> > >>
> > > --
> > > Burak ER 
> > > <
> > >  
> > > <mailto:>>
> > >
> > >
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> 
> -- 
> Burak ER 
> <>
> 
> 
> 

-- 
Burak ER 
<>