Some questions about the code

[autumn999999]

Thanks for your excellent open source work.
After reading the source code, there are 3 places I don't understand. I would be grateful if you could help me.

1. Why add a negative sign in lidar_camera_calib.hpp, like p.y=-y?

2. What is the meaning of this code in lidar_camera_calib.cpp, like V=n×nt, V=I-V, R=V*R?

3. Why the calculation of cost always used the pnp_list of calibs[2] in lidar_camera_multi_calib.cpp?

Is it more accurate to change this code to the following?