[Gmsh] c++ API - Import mesh vertices and elements

[Simone GREMMO [531257]]

Hi Ryan,
your code seems to be correct (by the way I am not a great expert of Gmsh source code).

I was thinking that maybe the problem is in the geometry definition: element orientations should be consistent all around the surface (triangle normals should point outward). Maybe some of your elements have opposite orientation and thus volume mesh cannot be generated?

On which geometry are you testing your program? If you have tried to generate the mesh using the GUI and you have succeeded, probably it's because Gmsh makes a check on orientation.

Simone
________________________________
De : rjdurscher at gmail.com [rjdurscher at gmail.com] de la part de Ryan Durscher [dursch at ufl.edu]
Envoyé : samedi 22 août 2015 6.00
À : Simone GREMMO [531257]
Cc : Gmsh; gmsh at geuz.org
Objet : Re: [Gmsh] c++ API - Import mesh vertices and elements

Simone,

Please see below for sample code. I have tried commenting out those line, but it resulted in the same issue. The error I am seeing is :

"Initializing memorypools.
  tetrahedron per block: 8188.
  Size of a point: 128 bytes.
  Size of a tetrahedron: 96 (96) bytes.
  Size of a shellface: 216 (216) bytes.
Error:  The point set is trivial."

These are tetgen outputs with the  "The point set is trivial" being a result of the 0 nodes being input into it. Incidentally if I call refineMesh it properly refines the surface mesh I am inputting into the gmshModel if I comment out the region stuff. From the GUI in order to get a volume mesh I have to use the elementary entities -> add -> volume then select the surface mesh (generated from step *** in the code). This creates a *.geo file which I cant figure out how to replicate though the API. The form of the *.geo file is:

Discrete Face(1) = {};
Surface Loop(3) = {1};
Volume(3) = {3};
Physical Surface(1) = {1};

I have been staring at this for a while now and any help would be greatly appreciated.

Thanks,
Ryan


// Gmsh headers
#include "Gmsh.h"
#include "GModel.h"
#include "GEntity.h"
#include "discreteFace.h"
#include "discreteRegion.h"
#include "MTriangle.h"
#include "MFace.h"

// *verts is a 3*numVerts array of coordinates verts(3*i + 0) = x, verts(3*i + 1) = y, and verts(3*i + 3) = z
// *conn is a 3*numTris array - define the triangles connectivity
int gmsh_Volume_Mesh(int numVerts,
                     int numTris,
                     double *verts,
                     int *conn)
{
    // Initialize variables
    int i,j;

    printf("USING GMSH\n");

    GmshInitialize();
    GmshSetOption("Mesh","Algorithm",1.);
    GmshSetOption("General","Verbosity", 100.);

    //Create Gmsh model and set the factory
    GModel *modelGmsh = new GModel;
    modelGmsh->setFactory("Gmsh");

    // Create a discrete face
    GFace *interFace = new discreteFace(modelGmsh,1);

    // Pack triangle verts  into vertex vector
    std::vector<MVertex*> vertex;
    vertex.resize((int) numVerts);
    for (i = 0 ; i < numVerts ; i ++) {

        vertex[i] = new MVertex(verts[3*i + 0],
                                verts[3*i + 1],
                                verts[3*i + 2],
                                interFace,
                                i+1); // Want index to start at 1
        // Add vertex to face
        interFace->addMeshVertex(vertex[i]);
    }

    // Pack connectivity of triangles into face
    for (i = 0; i < numTris; i++) {
        interFace->addTriangle(new MTriangle(vertex[conn[3*i + 0]-1],
                                             vertex[conn[3*i + 1]-1],
                                             vertex[conn[3*i + 2]-1]));/*,
                                             i+1,2));*/
    }

    printf("Number of elements in face = %d\n",interFace->getNumMeshElements());

    // Add face to model
    modelGmsh->add(interFace);

    // ****** modelGmsh->writeGEO("test.geo");
   // ****** modelGmsh->writeMSH("test.msh");

    // Create face loop - only 1 surface
    std::vector<GFace*> interfaceFace; //in my case the surface is given in one piece only
    interfaceFace.push_back(interFace);
    std::vector <std::vector<GFace*> > interfaceLoop;
    interfaceLoop.push_back(interfaceFace);

    // Create a physical region
    GRegion *regionInterface = modelGmsh->addVolume(interfaceLoop);

    //Add a volume physical entity
    regionInterface->addPhysicalEntity(1);

    //Add the region to the model
    modelGmsh->add(regionInterface);

    modelGmsh->writeGEO("test.geo");
    modelGmsh->writeMSH("test.msh");

    //Mesh the model
    //modelGmsh->refineMesh(1); // Refining the surface mesh works fine if I comment out the region stuff
    modelGmsh->mesh(3);

    /*printf("Num Regions = %d\n",gmshmodel->getNumRegions());
    printf("Num Faces = %d\n",gmshmodel->getNumFaces());
    printf("Num Edges = %d\n",gmshmodel->getNumEdges());
    printf("Num Verts = %d\n",gmshmodel->getNumVertices());*/

    delete modelGmsh;

    GmshFinalize();

    printf("Done meshing\n");
}
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