Question about the meaning of some variables

[achichichi]

Hello professor @chihyaoma :
Thank you for sharing your code, that's help me to learn more about this domain. And now I am reading the this part--pano_agent.py, but I have some confusion about the contents. I don't understand about the meaning of some variables.
ob、obs, and what information included.
_traj、traj, and what information included.
_ended、ended, and what information included.
xxxx、xxxx_idx (ex:viewpoints、viewpoint_idx, next_viewpoints、next_viewpoint_idx,...)

Could you please explain my confusion? Thank you.