how to get point in moving image, can you give an example?

[yangxue0827]

my code:

displacement = transformation.get_displacement()
warped_image = al.transformation.utils.warp_image(moving_image, displacement)
polybox = [[654, 260], [654, 290], [700, 290], [700, 260]]
warped_polybox = al.Points.transform(np.array(polybox).reshape([-1, 2]), displacement)
displacement = al.create_displacement_image_from_image(displacement, moving_image)

error:

Traceback (most recent call last):
  File "/Users/yangxue/Desktop/yangxue/code/airlab/examples/demo.py", line 151, in <module>
    main()
  File "/Users/yangxue/Desktop/yangxue/code/airlab/examples/demo.py", line 99, in main
    warped_polybox = al.Points.transform(np.array(polybox).reshape([-1, 2]), displacement)
  File "/Users/yangxue/Desktop/yangxue/code/airlab/airlab/utils/points.py", line 105, in transform
    raise Exception("Datatype of displacement field not supported.")
Exception: Datatype of displacement field not supported.

So I used the wrong displacement. How do I get the correct displacement? Can you give an example?