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

rjdurscher at gmail.com rjdurscher at gmail.com
Sat Aug 22 01:37:26 CEST 2015


Hi Simone, 

I am trying to implement the same thing you describe here in my code with 
Gmsh. I have followed your code below exactly however I am unable to 
generate the volume mesh. Outputting a *.msh file (model->writeMSH()) at 
various stages  the problem seems to come about during "
regionInterface->addPhysicalEntity(1);" in which the previously defined 
surface mesh now disappears (according the *.msh file). Any help would be 
greatly appreciated. I am currently using the latest version of Gmsh 
(2.10.1). Furthermore any additional code you could share regarding your 
second post (meshing between two surface) would be greatly appreciated. 

Thanks, 
Ryan 
  

On Monday, February 9, 2015 at 6:41:49 AM UTC-5, Simone GREMMO [531257] 
wrote:
>
> 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
> ):
>
>  
>
> GmshInitialize();
>
>     GmshSetOption("Mesh","Algorithm",1.);
>
>     //Create Gmsh model and set the factory
>
>     GModel *modelGmsh = new GModel;
>
>     modelGmsh->setFactory("Gmsh");
>
>  
>
>     //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);
>
>     modelGmsh->add(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
>
>     interfaceFace.push_back(interfaceGmsh);
>
>     std::vector <std::vector<GFace*> > interfaceLoop;
>
>     interfaceLoop.push_back(interfaceFace);
>
>  
>
>     //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
>
>     regionInterface->addPhysicalEntity(1);
>
>     //Add the region to the model
>
>     modelGmsh->add(regionInterface);
>
>     //Mesh the model
>
>     modelGmsh->mesh(3);
>
>    
>  modelGmsh->writeGEO("/home/simoneg/Hexpress-Hybrid_projects/IncludeGmsh-HH/TESTGMSHAPI_keyword/interfaceVertGmsh.geo");
>
>     
> modelGmsh->writeMSH("/home/simoneg/Hexpress-Hybrid_projects/IncludeGmsh-HH/TESTGMSHAPI_keyword/interfaceVertGmsh.msh");
>
>     delete modelGmsh;
>
> GmshFinalize();
>
>  
>
> //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;
>
>     mv.resize((int)numNodes);
>
>     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
>
>           
>                                        mv[inMesh.elem(cellCounter,1)],  
>
>                                  mv[inMesh.elem(cellCounter,2)]));
>
>             break;
>
>         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)]));
>
>             break;
>
>         default:
>
>             return false; 
>
>             break;
>
>         }
>
>     }
>
>     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.
>
> Simone
>
>  
>
> 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.
>
>  
>
> Simone
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.geuz.org/pipermail/gmsh/attachments/20150821/99367b3a/attachment-0003.html>


More information about the gmsh mailing list