We bought a Phantom 4 RTK with the D-RTK 2 Base Station in June 2019. I opted for getting the base station even though it was quite a bit more since it doesn’t rely on a cellular network. The system works really well, but a bit different than I’m used to as a civil engineer / surveyor.
Instead of placing the base station on a known control point which is tied to a mapping plane or a localized datum (which is how I tried to set it up the first time I used it) is an unnecessary and futile effort. Also, in the DJI RTK flight app on the controller there is a place to enter the base station coordinates in LLH, but if they are more than 50’ from where the base thinks it is, it will not apply them (which it explains in the app). After getting in the office I did some research and found some great info on DJI’s website, as well as Aerotas, explaining what is needed. DJI recommends just setting the base station in a safe place, no control point is needed.
The P4 RTK with the RTK base does not eliminate the need for a good GPS ground survey, however, I have been able to check coordinates and elevations on my best models within 0.03 ft (0.01 m)! Typically I can expect 0.05 ft (0.015 m) to 0.08 ft (0.024) which is within the expected accuracy of a GPS survey system.
I have not yet tried flying with only GNSS, nor have I flown with a P4 Pro so I can’t compare them.
I need to add that all positional and elevation rectifying is done inside Pix4D using the ground control points.