Could you explain why you compute the initial rotation vector like this?

[jimlinntu]

Hi, I found that you've tried to use the vertical vanishing point to give a good guess of the initial rotation vector. Although you eventually commented out the theta_0 computed from the vanishing point, I am curious about why you computed the rotation vector like that. (If possible, could you explain by an illustration?)

https://github.com/phulin/rebook/blob/4bc3920c226533a755e25c6d1eab6a7c8b44becc/rebook/dewarp.py#L1101-L1104

[phulin]

I wrote this code a long time ago, so I'm probably not in a much better position to draw this diagram than you are. I imagine I just found the vertical vanishing point on the projected plane and computed what the rotation angle must be.