[vtkusers] vtkExtractEdges and vtkUnstructuredGrid

[Martin Baumann]

Hi,

what must be contained in an vtkUnstructuredGrid so that vtkExtractEdges
can extract the edges of cells?
I use an vtkUnstructuredGrid that contains of points and cells, but
vtkExtractEdges doesn't extract anything:

extract_filter->GetOutput()->PrintSelf() returns
 Number Of Points: 0
 Number Of Cells: 0
while there are
 Number Of Points: 160
 Number Of Cells: 54
as I see using grid->PrintSelf().

My pipeline looks like
  vtkUnstructuredGrid* grid;
  grid = read_inp(filename);  // a self-made reader
  grid->PrintSelf(cout, 1);

  vtkExtractEdges* edge_filter = vtkExtractEdges::New();
  edge_filter->SetInput(grid);
  edge_filter->Update();
  edge_filter->GetOutput()->PrintSelf(cout,1);

Any idea?

Best regards, M.B.