[vtkusers] Problems building UnstructuredGrid, desperately needing help!

Tue Oct 25 11:27:18 EDT 2005

Hi Bruno, thanks for your reply!

Concerning the insertion of the ids, I'm not sure I have understood
what the InsertNextId is doing...

What I want to accomplish is this:
- insert cells into the grid so that my grid consists of several cells
of the same type (most often tetrahedra).

All the examples I have found on the net build a grid of only one cell...

My point coordinates lies in grid.coords (nnodes x 3 array) and the
connectivity info is in grid.connectivity (ncells x nnodes array)
How can I build the grid from this?

Lise

On 10/25/05, Bruno da Silva de Oliveira <bruno at esss.com.br> wrote:
> Hi Lise,
>
>  From the code you provided I can't be certain where the problem is. I
> can tell you thought that I have used InsertNextCell(cell_type, id_list)
> and it works fine.
>
> Hmm, looking at the code below, I see that you're inserting the ids of
> the points hard-coded to 1-4... this is mostly certainly wrong. The id
> must be the same id from the vtkPoints that you read the points
> coordinates into... also, don't forget to set them in the
> vtkUnstructuredGrid with SetPoints.
>
> HTH,
>
> Lise Angell wrote:
>
> >Hi everybody!
> >
> >I'm trying to translate C++ code to Python, but I'm having some
> >trouble so I would really appreciate some help (I'm not that
> >experienced with VTK).
> >
> >My program does the following:
> >- reads point coordinates and connectivity from file (not a vtk formatted file)
> >- builds a vtkUnstructuredGrid and visualizes it.
> >
> >The problem arises in the building of the unstructuredGrid...
> >
> >The method
> >vtkUnstructuredGrid::InsertNextCell(int type, vtkIdType npts, vtkIdType *pts)
> >seems to be unreachable from Python (although it works fine in C++,
> >for code sample, see below)...
> >When I try to run it I get
> >
> >Traceback (most recent call last):
> >  File "readBinarySimres.py", line 1092, in ?
> >    u_field = mount_vtk_structures(fields)
> >  File "readBinarySimres.py", line 828, in mount_vtk_structures
> >    vtk_field.InsertNextCell(cell_type, npts, pt_list)
> >TypeError: function takes exactly 2 arguments (3 given)
> >
> >
> >
> >So I tried to use the other method instead,
> >InsertNextCell (int type, vtkIdList *ptIds)
> >
> >for el in range (0,nel):
> >  id_list = vtk.vtkIdList()
> >  (cell_type, npts, id_list) = convertElm(grid, el, id_list)  #define
> >the connectivity in the cell
> >  vtk_field.InsertNextCell(cell_type, id_list)
> >
> >
> >def convertElm(grid, e, ids):
> >  vtk_cell_type=0; npt=0
> >  nsd = grid.nsd; nne = grid.nne
> >
> >  # check element type
> >  elm_type = grid.elm_type
> >
> >  if elm_type == 'ElmB4n2D':
> >    vtk_cell_type = VTK_QUAD
> >    #print 'element type ', vtk_cell_type
> >    npt = 4
> >    ids.InsertNextId(1)
> >    ids.InsertNextId(2)
> >    ids.InsertNextId(4)
> >    ids.InsertNextId(3)
> >  [...]
> >  return (vtk_cell_type, npt, ids)
> >
> >
> >
> >Now I get a Bus error while visualizing (with GeometryFilter,
> >WarpScalar, PolyDataNormals and PolyDataMapper)
> >
> >Any ideas what is wrong or how I can work around this?
> >
> >Best regards,
> >Lise
> >
> >(Running Mac OSX Tiger, python2.3 and VTK from cvs 11.oct 2005)
> >
> >###--------------------------------------------------------------------------
> >###--------------------------------------------------------------------------
> >
> >C++ code that works:
> >
> >   // Grab the grid and related parameters
> >  const GridFE& grid = scalar_field.grid();
> >  const int      nsd = grid.getNoSpaceDim();
> >  const int      nno = grid.getNoNodes();
> >  const int      nel = grid.getNoElms();
> >
> >  // Allocate Vtk data structures for the coordinates and data fields.
> >  vtkPoints* pts = vtkPoints::New();
> >  pts->SetNumberOfPoints (nno);
> >
> >  vtkDoubleArray* data = vtkDoubleArray::New();
> >  data->SetNumberOfValues (nno);
> >  //------------------------------------------------------------------------
> >  // First, tell vtk structures about the "geometry" (nodal coords & values)
> >  //------------------------------------------------------------------------
> >  for (int i = 0; i < nno; i++) {                // run through all nodes
> >    s = scalar_field.valueNode(i+1);
> >
> >    x[0]=grid.getCoor (i+1,1);  // x coordinate of node i+1
> >    x[1] = x[2] = scale*s;      // Assumes 1D,  scaled field values as 2nd/3rd
> >    if (nsd > 1)
> >      x[1]=grid.getCoor (i+1,2);  // y coordinate of node i+1
> >    if (nsd  > 2)
> >      x[2]=grid.getCoor (i+1,3);  // z coordinate of node i+1
> >
> >
> >    data->SetValue(i,s);      // put field value in vtk object
> >    pts->SetPoint(i,x);               // put points in vtk object
> >  }
> >  vtk_u_grid = vtkUnstructuredGrid::New();
> >
> >  vtk_u_grid->Allocate (nel,0);                   // set no of elements
> >  vtk_u_grid->SetPoints (pts);                    // put points in grid
> >  vtk_u_grid->GetPointData()->SetScalars(data);  // put field values in grid
> >
> >  //---------------------------------------------------------
> >  // Next, tell vtk grid structure about the element topology
> >  //---------------------------------------------------------
> >
> >  // Maximum 8 nodes in the allowable Vtk cell types.
> >  int vtk_cell_type = 0;
> >  int npt = 0, pt_list[8] = { 0, 0, 0, 0, 0, 0, 0, 0 };
> >
> >  for (int e = 1; e <= nel; ++e) {
> >    convertElm(grid, e, vtk_cell_type, npt, pt_list);
> >    vtk_u_grid->InsertNextCell (vtk_cell_type, npt, pt_list);
> >  }
> >
> >
> >
> >###--------------------------------------------------------------------------
> >###--------------------------------------------------------------------------
> >
> >
> >
> >--
> >"Je forme une entreprise qui n'eut jamais d'exemple,
> >et dont l'exécution n'aura point d'imitateur."  J-J Rousseau
> >_______________________________________________
> >This is the private VTK discussion list.
> >Please keep messages on-topic. Check the FAQ at: http://www.vtk.org/Wiki/VTK_FAQ
> >Follow this link to subscribe/unsubscribe:
> >http://www.vtk.org/mailman/listinfo/vtkusers
> >
> >
> >
>
> --
> Bruno da Silva de Oliveira
> bruno at esss.com.br
> ESSS - Engineering Simulation and Scientific Software
> http://www.esss.com.br
>
> _______________________________________________
> This is the private VTK discussion list.
> Please keep messages on-topic. Check the FAQ at: http://www.vtk.org/Wiki/VTK_FAQ
> Follow this link to subscribe/unsubscribe:
> http://www.vtk.org/mailman/listinfo/vtkusers
>

--
"Je forme une entreprise qui n'eut jamais d'exemple,
et dont l'exécution n'aura point d'imitateur."  J-J Rousseau