I am using two gps modules with blunos (bluetooth arduinos) too get the distance between them and display it on a phone. This has worked great and on avg Im getting the expected 5m inaccuracy.
However I would like to get better accuracy so I was looking into GNSS with rtk. From my understanding RTK uses an unmoving base station with known coordinates and works out the error the GNSS of the base is getting. It then sends this error to my rover which corrects its own readings.
If this is correct (if not please explain how it does work) then do all GNSS in an area have the same error.
If they do, do I need the rtk with the GNSS or can I just use two and they will measure the distance between them accurately even if they don't measure their locations accurately