Your phone's GPSThe US satellite navigation system. People often use "GPS" to mean all satellite positioning.More is usually right to within a few meters. That's fine for finding a coffee shop. It is not fine for mapping a building site, where you need to be right to within a couple of centimeters (about an inch).
RTK fixes this. RTK stands for real-time KinematicMeasuring while moving. The "K" in RTK and PPK.More. It is a way to get centimeter-level positions from GNSSGlobal Navigation Satellite System. The general name for GPS (USA) and the other satellite systems like GLONASS, Galileo and BeiDou.More, which is the general name for GPS and the other satellite systems.
Here is how it works. A base receiver sits on a spot whose position is already known. It watches the same satellites as your rover (a survey pole receiver or a drone). The base can see how far off the satellite signals are right now. It sends those "CorrectionsLive info from a base station about how far off the satellite signals are, so your rover can cancel out the error.More" to the rover. The rover uses them to cancel out most of the error.
Think of it like two friends with the same broken watch. One friend knows the real time and texts the other: "Your watch is 3 minutes fast." Now both are right.
The really precise part comes from counting the waves of the satellite signal. NGSNational Geodetic Survey. The part of NOAA that runs the official US coordinate system, CORS and OPUS.More (the National Geodetic Survey, part of NOAANational Oceanic and Atmospheric Administration. The US agency that includes NGS and runs the CORS network.More) describes RTK as working out the exact whole number of signal waves between the satellite and the receiver. Once the rover has that count, it has a fixed solution. See Fix vs float.
Do you need it?
- Probably yes if your results have to hold up: survey work, StakeoutUsing a GPS rover to find and mark planned points on the ground, like where a building corner goes.More points, As-builtA survey of what was actually built, to compare with the plans.More drawings, earth volumes you may need to defend, or drone maps where you want to set out fewer ground targets.
- Maybe not for inspections, marketing photos or progress pictures. Being a few meters off is fine there.
- Think about PPKPost-processed kinematic. Like RTK, but the corrections are applied after the job using recorded data, so no live link is needed.More if you can't keep a live internet or radio link in the field. See RTK vs PPK.
Where to get corrections
Find free state networks and paid services on the state map. See how far you are from a Base stationA GNSS receiver sitting still on a known spot. It figures out how wrong the satellite signals are right now and shares that as corrections.More with the Nearest base station tool. Or let the Which service fits me picker make a short list for you.