| None of the non-rtk ones approach this accuracy solely because without knowing the varying local atmosphere error you cannot, even in theory, get that accuracy from GPS. All the GPS and RTK systems I've been working on use all possible signals from all the GNS systems (except I disable Russian GLONASS at the moment due to war fueled sketchiness). To get them to work well you need good antennas that capture them all, and good wiring to keep phases clean. Noise kills precision here. Find a textbook that does all the math and physics behind all the GNS systems, and you'll find a chapter on errors introduced by atmosphere. RTK gets around this by having a known nearby (and hence nearly identical atmosphere path) point also get all the GNS signals, do the same computation, and send correction data in realtime to your RTK receiver. There's also some neat stuff about signal phase that adds a little more precision over standard GPS. I've now built multiple complete RTK and multi-RTK systems, and have been up and down all the stacks from many angles, working on pushing things to the limit, for industrial uses. RTK really goes beyond anything I've seen in GPS, at any price. There's simply no way to realize all your signals are delayed or bent by local ionized or magnetic storms causing signal delay without some other truth data. |