[vtkusers] Problems building UnstructuredGrid, desperately needing help!

Wed Oct 26 05:12:02 EDT 2005

Ah, it worked!
Thanks a lot, you really saved my day:)

Lise

On 10/25/05, Bruno da Silva de Oliveira <bruno at esss.com.br> wrote:
> Hi Lisa,
>
>
> Well, a cell is made of point ids, that reference geometry, which
> finally define the complete shape of the cell.
>
> Suppose we have this point list:
>
> 0 - 0, 0, 0
> 1 - 1, 0, 0
> 2 - 0, 1, 0
> 3 - 0, 0, 1
> 4 - 2, 0, 0
> 5 - 1, 2, 0
> ...
>
> and so on. Suppose the first cell (a tetra) is made of points 2, 3, 4
> and 1. To generate this cell you would do:
>
> ids = vtk.vtkIdList()
> ids.InsertNextId(2)
> ids.InsertNextId(3)
> ids.InsertNextId(4)
> ids.InsertNextId(1)
>
> grid.InsertNextCell(VTK_TETRA, ids)
>
> Hope the example made things a little clear.
>
> So, I believe your grid.connectivity list is actually an array of cell
> -> ids of the points that form that cell, right? So to build all your cells:
>
> for ids in grid.connectivity: # an array of point ids for each cell
>    id_list = vtk.vtkIdList()
>    for id in ids:
>        id_list.InsertNextId(id)
>    if len(ids) == 4: # a tetra
>        cell_type = VTK_TETRA
>    elif ... # other types of cells
>    ...
>
>    grid.InsertNextCell(cell_type, id_list)
>
>
> Setting up your point coordinates is pretty straighforward.
>
> HTH,
>
>
> Lise Angell wrote:
>
> >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
> >
> >
> >
>
> --
> 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:
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>

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