Four Ways to Reach the Same Coordinate
Every companion so far in this series has assumed one particular way of producing a coordinate: a rover, a base or network correction, and a real-time carrier-phase solution. That assumption was stated plainly at the time, and it was always going to need its own book eventually. This is that book.
RTK is one member of a family of correction methods, not the only one. PPK, PPP, and PPP-RTK each solve a related problem in a genuinely different way, and choosing well between them means understanding what each one actually trades away.
The Same Destination, Different Roads
Every method this companion covers is ultimately trying to answer the same question the rest of this series has asked from the very beginning: where is this antenna, right now, expressed in a trustworthy reference frame. RTK answers it one way. Post-processed kinematic surveying, PPK, answers it in a way that looks almost identical on paper but behaves very differently in practice. Precise point positioning, PPP, answers it in a way that needs no local reference point at all. PPP-RTK, using a newer correction format called SSR, tries to combine the best properties of several of these approaches at once.
Why This Companion Exists
A crew choosing between these methods without understanding what actually distinguishes them tends to pick based on habit, or based on whatever a particular piece of software defaults to, rather than based on what the job actually needs. A remote pipeline corridor with no cellular coverage, a drone mapping mission flying too fast for a live correction link, a maritime survey with no nearby base station for a thousand kilometers, and a construction site with excellent network RTK coverage all call for genuinely different answers, and this companion exists to make that choice a deliberate one instead of a default one.
RTK is not simply the modern standard that every other method is a compromise away from. PPK, PPP, and PPP-RTK were each developed to solve problems RTK cannot solve at all, not merely to work around RTK being temporarily unavailable.
What This Companion Assumes Already
This companion assumes the reader already understands what a reference frame is, what an epoch is, what a geoid model does, and how to evaluate whether an RTK position deserves to be trusted, all covered at length earlier in this series. None of that changes here. What changes across this companion is entirely how the raw position gets solved in the first place, before any of those later questions ever come into play.
If PPK, PPP, and PPP-RTK all eventually produce a coordinate, does everything this series has already covered, reference frames, epochs, geoid models, verification, still apply to them? Yes, entirely. Only the method of solving the raw position changes. Everything built on top of that position works exactly the same way regardless of which method produced it.
RTK is one correction method among several, not a default that others merely approximate. PPK, PPP, and PPP-RTK each trade speed, precision, and infrastructure requirements differently, and this companion exists to make that trade a deliberate choice rather than a habit.
Before contrasting RTK against anything else, it is worth being precise about exactly which parts of RTK the rest of this companion will keep, and which parts other methods are about to do differently.