CGAL users discussion list

[Burak ER <>]

Hi,

Would you please guide me to achieve a meshing procedure where I only
set the minimum element volume. Therefore, I have the ability to change
the mesh density with having it uniform with using a single parameter.
Is it possible? Can you provide me a simple example of code?

Thank you in advance.

Burak 

Cum, 2013-10-25 tarihinde 16:48 +0200 saatinde, Sebastien Loriot
(GeometryFactory) yazdı:
> On 10/25/2013 04:44 PM, Burak ER wrote:
> > 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.
> 
> 
> I guess it's coming from the way you protected the sharp edges. You need 
> to reduce the number of protecting balls on the sharp edges.
> 
> Sebastien.
> 
> 
> >
> > 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 
<>