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

Simone GREMMO [531257] Simone.GREMMO at umons.ac.be
Mon Feb 9 10:04:52 CET 2015

Dear all,
I think I have partially solved my problem. Here is the code that I have written and let me to create the volume mesh (Thanks to Mikhail for his suggestion in this answer: http://geuz.org/pipermail/gmsh/2015/009536.html):

    //Create Gmsh model and set the factory
    GModel *modelGmsh = new GModel;

    //GFace is defined by a mesh and not through GVertex and GEdge
    GFace *interfaceGmsh = new discreteFace(modelGmsh,1);
    //Function that loops over mesh vertices and elements and import them in a gmsh structure [see at the bottom of the main function]
    importSurfaceMeshintoGmsh(interface, interfaceGmsh);

    //Using the previously defined surface, define a surface loop, used to enclose a volume
    std::vector<GFace*> interfaceFace;  //in my case the surface is given in one piece only
    std::vector <std::vector<GFace*> > interfaceLoop;

    //Add the volume enclose by the surface loop to the model and create the related GRegion
    GRegion *regionInterface = modelGmsh->addVolume(interfaceLoop);
    //Add a volume physical entity
    //Add the region to the model
    //Mesh the model
    delete modelGmsh;

//Function to import the mesh in a Gmsh structure
//inMesh is the input mesh, created with another tool
//gmshMesh is the structure containing the inMesh, but that can be used by Gmsh to generate the volume mesh
bool importSurfaceMeshintoGmsh(const My_Mesh &inMesh, GFace *gmshMesh)
    My_int numNodes = inMesh.numVerticies(); //get the number of vertices from the inMesh
    My_int numCells = inMesh.numCells(); ////get the number of elements from the inMesh

    //Get all the vertices from the mesh
    std::vector<MVertex*> mv;
    for (MC_Index nodeCounter = 0; nodeCounter < numNodes; nodeCounter++)
        My_Coord3D coordHH = inMesh.vertex(nodeCounter); //a 3 dimensions vector with the vertex coordinates
        mv[nodeCounter] = new MVertex((double)coordHH[0], (double)coordHH[1], (double)coordHH[2],gmshMesh, nodeCounter+1);
        gmshMesh->addMeshVertex(mv[nodeCounter]); //add the vertex to the mesh

    //Get all the elements from the mesh
    for (My_int cellCounter = 0; cellCounter < numCells; cellCounter++)
        My_int numVertCell = inMesh.numElems(cellCounter); //for element #cellCounter, get the number of vertices
        switch (numVertCell)
        case 3: //triangle
            gmshMesh->addTriangle(new MTriangle(mv[inMesh.elem(cellCounter,0)],   //extract the vertexID for element #cellCounter
        case 4: //quadrangle
            gmshMesh->addQuadrangle(new MQuadrangle(mv[inMesh. elem(cellCounter,0)],
                                                                                                                mv[inMesh. elem(cellCounter,1)],
                                 mv[inMesh. elem(cellCounter,2)],
                                 mv[inMesh. elem(cellCounter,3)]));
            return false;
    return true;

This code generates a mesh in a volume without any hole inside. Does anyone know how to add a hole inside the volume and mesh the region between the two surfaces?
The .geo commands looks like:
Merge "interfaceMesh.msh";
Surface Loop(3) = {1};
Merge "envelopeMovingMesh.msh";
Surface Loop(4) = {2};
Volume(1) = {3,4};
Physical Volume(1) = {5};

Thanks for your help.

Dear all,
I have included Gmsh as library in my c++ program and I need to use it to mesh a volume region bounded by a surface mesh: in my program I have defined a surface mesh and I need to import its vertices and elements into a gmsh structure to be able to create a volume mesh starting from this surface.
Steps to do so, as far as I can understand, are:

-          Declare a GModel* that will contain the surface

-          Add a GFace* into the GModel

-          Add vertices and cells to the GFace* (get them from the mesh created in my program). Actually define a mesh for this GFace object

-          Create the volume mesh

Is this correct? Does anyone have any suggestion on how to write this portion of code?

PS I have already looked at the example in utils/api_demos/mainSimple.cpp and have adapted it to my case, but I would rather avoid reading/writing files to transfer meshes between the my program and gmsh to avoid performance issues.

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