CGAL users discussion list

[Burak ER <>]

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 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.

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
Research Assistant
Faculty of Natural Sciences & Engineering
Bursa Technical University

mailto:burak.er@btu.edu.tr
https://github.com/burak-er

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