    integ = vtkRungeKutta4()

    streamer = vtkStreamTracer()
    streamer.SetInputConnection(reader.GetOutputPort())
    streamer.SetStartPosition(0.1, 2.1, 0.5)
    streamer.SetMaximumPropagation(500)
--
    rk4 = vtkRungeKutta4()
    streamer = vtkStreamTracer()
    streamer.SetInputData(pl3d_output)
    streamer.SetSourceData(seeds)
    streamer.SetMaximumPropagation(100)
    streamer.SetInitialIntegrationStep(0.2)
