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?)

rebook/rebook/dewarp.py

Lines 1101 to 1104 in 4bc3920

	xz_ratio = -f / vx # theta_x / theta_z
	norm_theta_sq = (atan2(np.sqrt(vx ** 2 + f ** 2), vy) - pi) ** 2
	theta_z = np.sqrt(norm_theta_sq / (xz_ratio ** 2 + 1))
	theta_x = xz_ratio * theta_z

[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.