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I've read a number of articles on RTK GPS. I'm only familiar with using RTK GPS with an RTK Base Station, and I understand how the corrections can be broadcast to a rover. When would you use RTK GPS without using a base station, and is this practical?

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In all cases, L-code receivers need to resolve the "integer ambiguity" between signals received from the observable satellites in order to achieve their differential GPS accuracies.

So, I believe there are two questions you may be asking: 1) How can I achieve differential GPS accuracy using a single roving L-band receiver? or 2) How can I get the most out of an RTK receiver in autonomous mode?

For question 1: Alternatives to a "traditional" base station include subscribing to a virtual reference station network. -- these subscription services deliver real-time correction parameters over cellular-IP addresses.

  • the corrections are "smeared" (read triangulated, least-squares averaged) over a mesh of correction base stations
  • uploaded to the internet then made available for download.

Receivers download them and apply the differential corrections on-the-fly during RTK observations just as though they were receiving a signal from a dedicated base on a known point.

Question alternative 2 is less beneficial as autonomous L-band positioning is only slightly more accurate than C-code autonomous positioning. The better option to get full value from a single L-band receiver is PPK (post-processed Kinematic) where multiple autonomous surveys can be bundle-adjusted together with known baselines to reduce uncertainties and obtain RTK accuracy.

NOTICE that nowhere did I address any issue of "precision" because that is a non-issue when comparing multiple methods using a single device -- the precision is constant (and assumed to be arbitrarily "precise-enough".)

Bottom line, the satellite constellation, atmosphere, and correction baselines will dominate the solution accuracy and the precision is device-dependent.

  • Thanks for your answer, this helps clarifies it. So this brings up another question that might be missing from my fundamental understanding: is the reason base stations are used with RTK is because of integer ambiguity? – Otto Nahmee Sep 12 '16 at 15:30
  • Sort of...very fundamentally: multiple simultaneous observations are necessary because of the integer ambiguity. Using a base station (ie a fixed point) as one of those simultaneous observations simply helps invert the matrix math to solve for multiple unknowns (x, y, z, i). However, you could run enough rovers with overlapping observations, or you could do an old fashioned 'antenna swap' where two rovers exchange observation positions while 'seeing' the same sky. -- that gives PPK software enough 'knowns' to solve the integer ambiguity also. – JasonInVegas Nov 9 '16 at 0:52

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