animated frames do not match the same frames when plotted

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Assessment

Difficulty
3/5
Estimated time
1-2 days
Newbie friendliness
42/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Stale
Tech stack
python
Domain
computer-graphics

Research direction

Open the linked animate_start_to_end.ipynb.json notebook and reproduce the SE3 animation using the reported poses. Then inspect the animate method to compare behavior with and without the start argument. Done means the animation begins at the supplied start pose and ends at the pose on which animate is called.

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Description

Hi,

first of all, I would like to express my appreciation for this great python package.

I did some experiments with SE3 objects and animations and found a behavior of the animate method that I can't explain.
If SE3 is animated without the start argument, everything works as expected. The same applies if you explicitly start at SE3(). However, if the start is an arbitrary pose, the animated frame does not start in the expected pose and does not end at the pose for which animate is called.

t = SE3([
    SE3(),
    SE3([-1,0,2]),  # start
    SE3.RPY([10, 5, -20], unit='deg') * SE3([1,2,1]), # end
])
t[0].plot(frame='0', color='black')
t[1].plot(frame='1', color='blue')
t[2].plot(frame='2', color='red')
t[2].animate(frame='2m', start=t[1], color='purple')    # frame does not move from t[1] to t[2] as I would expect
# t[2].animate(frame='2m', start=t[0], color='purple')  # ok, frame moves from t[0] to [2]
# t[2].animate(frame='2m', color='purple')              # ok, frame moves from origin to t[2]

I have also summarized the experiment in a jupyter notebook animate_start_to_end.ipynb.json (remove the json ending to open it as notebook).
Can you please check it and let me know if I am doing something wrong.

Best regards.

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