The Many Shapes of RTK
The last chapter treated RTK as a single, settled baseline: real time, a nearby reference, immediate ambiguity resolution. That is accurate as far as it goes, but it hides something worth surfacing before moving on. RTK itself is delivered through several genuinely different arrangements, and choosing among them is its own practical decision, well before PPK, PPP, or PPP-RTK ever enter the picture.
RTK's underlying mechanism never changes, but the physical or network arrangement supplying the correction varies considerably: a single dedicated local base, a wide regional network of continuously operating stations, or a specific public network run by a state agency, each with its own practical trade-offs.
A Local Base and Rover, Talking Directly
The most self-contained arrangement is a single base, set up over a known point, communicating directly with one or a few rovers over its own dedicated radio link. Traditionally that link has meant a licensed UHF radio, chosen for its long range and reliability. It is no longer the only practical option. A local base and rover can just as easily communicate over WiFi at short range, over a low-power, license-free protocol like LoRa built specifically for long-range, low-bandwidth telemetry, or over an inexpensive point-to-point radio built around the ESP-NOW protocol.
A local base and rover only need to exchange a modest stream of observation data, not a high-bandwidth connection. That modest requirement is exactly why LoRa, WiFi, and ESP-NOW-based radios have become practical, affordable alternatives to a dedicated UHF survey radio for many jobs.
Real-Time Networks: Many Bases at Once
A real-time network, often shortened to RTN, replaces a single dedicated base with a permanent, wide-area system of continuously operating reference stations, generating synthetic observations for any rover anywhere within its coverage, typically through a modeled virtual reference station as covered earlier in this series. A crew working within an RTN's coverage area never sets up a base at all, trading the one-time cost and effort of owning and deploying a base station for a subscription or usage fee and a dependence on that network's own reach and reliability.
A real-time network is not simply a bigger version of a single local base. It is a fundamentally different arrangement, replacing a piece of equipment a crew owns and deploys with an ongoing service the crew subscribes to and depends on.
Statewide CORS: Often Free, Often Overlooked
A specific, common example of a real-time network deserves its own mention because it is so often overlooked: many state transportation and mapping agencies operate their own statewide network of continuously operating reference stations (CORS), originally built to support the agency's own survey and engineering work. A great many of these statewide networks make their real-time corrections available to the public over NTRIP at no charge at all, a genuinely useful resource that plenty of working crews never realize is sitting there, already paid for by public infrastructure.
A project sits well within a state's published CORS coverage area, and the crew is debating whether to deploy their own base station or pay for a commercial network subscription. Is there a third option worth checking first? Very possibly. Many states provide free, public NTRIP access to their own statewide CORS network, and it costs nothing to check before committing to either alternative.
Reaching NTRIP Without Cellular at All
Every NTRIP-based option in this chapter, an RTN subscription, a statewide CORS network, or a commercial service, assumes some kind of internet connection is available to carry it, and cellular data has traditionally been the default assumption. That assumption no longer has to hold everywhere it once did. Compact satellite internet terminals, Starlink Mini among them, now make a genuine broadband connection available in places cellular coverage has never reached, small enough to set up at a job site in minutes and reliable enough to carry an ordinary NTRIP stream without difficulty. Many modern vehicles offer a similar solution built in, providing their own WiFi access point over an onboard satellite communications system, turning a work truck already on site into an internet connection a rover or data collector can simply join.
An NTRIP correction has modest bandwidth needs, well within what a compact satellite terminal or a vehicle's onboard satellite connection can comfortably carry. The limiting factor for reaching a statewide CORS network or a commercial correction service was rarely bandwidth. It was simply having any internet connection to begin with, and that constraint is loosening quickly.
Choosing Among RTK's Own Options
None of these arrangements changes what RTK actually is. A local base, an RTN, and a statewide CORS network all still deliver live reference observations to difference against, resolving ambiguities immediately in the field. What changes is who owns the infrastructure, how wide its coverage reaches, what it costs, and how quickly a crew can be up and running on a given day. That choice belongs entirely within RTK, before the rest of this companion's comparison against PPK, PPP, and PPP-RTK ever becomes relevant.
RTK is delivered through several distinct arrangements, a local base and rover over a direct radio link, a wide-area real-time network, or a specific public statewide CORS network over NTRIP, each with its own cost, coverage, and setup trade-offs. Recognizing these options is itself a practical decision, separate from choosing among RTK, PPK, PPP, and PPP-RTK.
With RTK's own variety on the table, this companion can now return to the two-question framework and use it to place every other correction method against that same baseline.