    reader = vtkXMLUnstructuredGridReader()
    reader.SetFileName(fn)
    reader.Update()

    converter = vtkUnstructuredGridToExplicitStructuredGrid()
    converter.GlobalWarningDisplayOff()  # hide VTK errors
--
    reader = vtk.vtkXMLUnstructuredGridReader()
    reader.SetFileName(file_name)
    reader.Update()  # Needed because of GetScalarRange
    output = reader.GetOutput()
    # scalar_range = output.GetScalarRange()

