What Is RTK GPS? Centimeter-Level Positioning, Explained in Plain English
RTK (Real-Time Kinematic) is a technique that upgrades ordinary satellite positioning from meter-level to centimeter-level accuracy — in real time, while the vehicle is moving. It works by adding a second, stationary receiver (a base station) that measures the errors in the satellite signals and streams corrections to the moving receiver (the rover) on your drone. With a good correction link and open sky, an RTK rover holds its position estimate inside a 1–2 cm circle, versus 1.5–3 m for a standard GPS module — roughly 100× tighter.
This page is the plain-English background for our MicoAir MA-RTK Series User Manual and RTK Setup Guide. If you already know what RTCM and a FIX are, jump straight there.
Why is normal GPS only accurate to a few meters?
A GNSS receiver computes position by timing radio signals from satellites 20,000 km away. Several error sources corrupt that timing, and they are all outside your control:
| Error source | What it does | Typical size |
|---|---|---|
| Ionosphere | Charged particles bend and slow the signal, varying by time of day and solar activity | 2–5 m |
| Troposphere | Weather-dependent delay in the lower atmosphere | 0.5–1 m |
| Satellite clock & orbit | The satellite's broadcast position/time is slightly wrong | 1–2 m |
| Multipath | Reflections off buildings and terrain mix with the direct signal | 0.5–2 m |
A single receiver can average and model these, but it can never measure them — it has no way to tell how much of what it sees is truth and how much is error. That is the ceiling of every standalone GPS module, no matter how good.
The RTK trick: a second receiver that knows where it is
Put a receiver on a tripod and let it sit still. Its true position never changes — so every wobble in its computed position is, by definition, error. And because the base and your drone are within a few kilometers of each other, they look through the same patch of ionosphere at the same satellites — they experience almost identical errors at the same moment.
So the base measures the error in real time and broadcasts it. The rover subtracts it. What's left is nearly pure geometry.
There is a second ingredient that gets you from "sub-meter" to "centimeter": carrier-phase measurement. A normal receiver reads the data message encoded on the satellite signal — coarse, like reading street signs. An RTK receiver additionally counts the individual waves of the carrier signal itself. Each wave of the GPS L1 carrier is only 19 cm long, and the receiver tracks its phase to a fraction of a percent. Once the rover figures out the exact whole number of waves between it and each satellite (called ambiguity resolution — this is the moment your GCS reports RTK FIXED), its range measurements become millimeter-grade.
The words you'll see in Mission Planner / QGroundControl
| Term | Plain-English meaning |
|---|---|
| RTCM | The standard message format for correction data (RTCM 3.x). What the base sends, what the rover eats. |
| 3D Fix / Single | Ordinary GPS solution, no corrections. 1.5–3 m. |
| DGPS | Corrections applied, carrier phase not yet resolved. Sub-meter-ish. |
| RTK FLOAT | Carrier phase in use but wave-count ambiguity not yet locked. ~0.1–0.5 m. Normal for the first 1–2 minutes. |
| RTK FIXED | Ambiguity resolved. 1–2 cm. This is the goal state. |
| Baseline | Distance between base and rover. Accuracy specs read "1 cm + 1 ppm": add 1 mm per km of baseline. At 5 km you're still ~1.5 cm. |
| NTRIP | RTCM delivered over the internet from a public/commercial reference network instead of your own base. |
| PPK | Post-Processed Kinematic — log raw data, compute the trajectory after the flight. No live link needed, but no live precision either. |
What RTK does not fix
Being honest about the limits saves debugging time later:
- It still needs sky. RTK refines satellite geometry; it cannot conjure satellites indoors, under dense canopy, or in a street canyon. (Multi-band receivers like the ones in the MA-RTK series tolerate partial obstruction far better, but nothing flies RTK FIXED in a warehouse — that's what optical flow is for.)
- It needs the correction link alive. Lose the radio/telemetry stream for more than a few seconds and the solution degrades from FIXED → FLOAT → ordinary GPS.
- It's relative to the base. If you guessed the base position ("survey-in"), your absolute coordinates are only as good as that guess — but they are consistently wrong, which is fine for repeatable missions. Put the base on a known surveyed point when absolute truth matters.
Do you actually need RTK on your drone?
Clear yes:
- Mapping & surveying — centimeter geotags mean fewer ground control points and orthomosaics that line up.
- Drone light shows & swarms — hundreds of aircraft holding formation a couple of meters apart cannot tolerate meter-level wander. (This is exactly the niche the low-cost MA-RTK-AIR-626 was built for.)
- Precision agriculture — repeatable rows, spray lines that don't overlap.
- Precision landing / docking — returning to a charging pad or moving platform.
- Inspection near structures — with dual-antenna heading (MA-RTK-AIR-982), yaw stays true next to steel where compasses lie.
Probably no: casual FPV, line-of-sight cruising, any flight where "within a meter or two" is fine. A good dual-band module like the MG-F10-C costs a third as much and needs zero infrastructure.
RTK vs PPK vs NTRIP — which correction path?
- Own base + radio (what the MA-RTK-BASE kit does): works anywhere with no internet and no subscription; ~1 km+ range depending on the telemetry radio; you own the whole chain.
- NTRIP over internet: no base to carry, but needs cell coverage at the field and, in many regions, a paid subscription; baseline to the nearest reference station can be tens of km.
- PPK: most robust in the air (no link to drop) but you only get precision after post-processing — useless for live formation flying or precision landing.
For self-contained field work with ArduPilot/PX4 drones, a local base with radio broadcast is the simplest reliable option — the RTK Setup Guide walks through both the ground-station relay and direct radio broadcast versions.
Frequently asked questions
How accurate is RTK really? With a fixed solution and a short baseline: 1–2 cm horizontal, 2–3 cm vertical for typical drone-grade receivers (e.g. 0.8 cm + 1 ppm horizontal for the UM982). FLOAT solutions are decimeter-grade.
How far can the rover be from the base station? Corrections stay valid to roughly 10–20 km (accuracy degrades ~1 mm/km). In practice the limit is usually your radio link, not the math.
Does RTK replace the compass? Single-antenna RTK does not — it fixes position, not heading. A dual-antenna receiver like the MA-RTK-AIR-982 does measure true heading from GNSS, replacing the magnetometer entirely. See the dual-antenna heading section of the setup guide.
How long does it take to get RTK FIXED? With a multi-band receiver, open sky and a healthy correction stream: typically 30 seconds to 2 minutes after corrections start flowing.
Do both base and rover need to be the same brand? No. RTCM 3.x is a standard; any base that emits it can serve any rover that eats it. Matching multi-band capability helps convergence speed.
Where to go next
- MicoAir MA-RTK Series User Manual — specs, wiring and firmware setup for the MA-RTK-AIR-982 / 626 / F9P rovers and the MA-RTK-BASE station.
- RTK Setup Guide — deploy the base, stream corrections via Mission Planner or radio, reach RTK FIXED, add dual-antenna heading.
- Shop the hardware: MicoAir RTK modules and base station at Robofusion — ships worldwide from our Hong Kong warehouse.