    rt = vtkRTAnalyticSource()
    rt.SetWholeExtent(-3, 3, -3, 3, -3, 3)
    grad = vtkImageGradient()
    grad.SetDimensionality(3)
    grad.SetInputConnection(rt.GetOutputPort())
    brown = vtkBrownianPoints()
--
    rt = vtkRTAnalyticSource()
    rt.SetWholeExtent(-3, 3, -3, 3, -3, 3)
    grad = vtkImageGradient()
    grad.SetDimensionality(3)
    grad.SetInputConnection(rt.GetOutputPort())
    brown = vtkBrownianPoints()
--
    rt = vtkRTAnalyticSource()
    rt.SetWholeExtent(-2, 2, -2, 2, 0, 0)

    # Take the gradient of the only scalar 'RTData' to get a vector attribute
    grad = vtkImageGradient()
    grad.SetDimensionality(3)
--
    rt = vtkRTAnalyticSource()
    rt.SetWholeExtent(-2, 2, -2, 2, 0, 0)

    # Take the gradient of the only scalar 'RTData' to get a vector attribute
    grad = vtkImageGradient()
    grad.SetDimensionality(3)
