Seeking Recommendations for Here's many RTK GPS and Tips

Hello.

I’m planning to use RTK GPS for measuring two point’s distance and bearing.
I will check ship’s light viewable angle with drone, so the disatance and bearing between two pixhawk should be calculated real-time.
I programmed custom mission planner plugin for acheving this function.

but, I don’t know about RTK GPS. I have not use it before.

So I have two questions :

(1) can 1 RTK base be connected to two rover simultaneosly?

I have to measure two point’s distance. one is ArduRover and one is ArduCopter.

(2) for this usage, what RTK GPS do you recommend?

what is difference with Here+ and Here3+ and Here3?

yes, you can, it is a one way comm, corrections need to be sent to rovers, and there can be as many rovers as you want for one base.

Here3+, Here4 and HerePro in increasing order of quality. For base you will need to pair Here3+ with Here+ Base, its only L1 band. Here4 needs to be paired with Here4 base, its L1 and L5 (some config is required to enable use of L5) and will give you much better results at reasonable value. HerePro (L1, L2 and E5) can act as both base and rover, and can also do onboard GPS logging for PPK, and has much better GPS signal reception than Here4 and Here3+.