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Re: [cgal-discuss] "About conserving the boundary polyhedron while tetrahedral discretization"


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  • From: "Sebastien Loriot (GeometryFactory)" <>
  • To:
  • Subject: Re: [cgal-discuss] "About conserving the boundary polyhedron while tetrahedral discretization"
  • Date: Mon, 28 Oct 2013 11:14:35 +0100
  • Organization: GeometryFactory
The way protected features are sampled is controlled by the parameter edge_size in the mesh criteria. As already said by Laurent in another thread, set it to facet_size.

Sebastien.


On 10/28/2013 08:33 AM, Burak ER wrote:
Hi,

I really need an answer urgently, please.

Burak

Cts, 2013-10-26 tarihinde 23:18 +0300 saatinde, Burak ER yazdı:
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
<

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--
Burak ER
<>







--
Burak ER
<>






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