Question about lidar-camera extrinsic calibration problem and how to build residuals.

[wddr955]

Excellent work!

I have two questions that I can't figure out.

1. I guess E_C is as close to 0 as better, so why there is not a square or absolute operation in the below formula?
   

2. After watching Question about vpnp cost function #2, i still can't figure out the residuals' building process below, can you show me more detail or give me more reference?
   

(3. What's vPnP?)
Looking forward to your reply, thanks!!!