What RTK is and how NTRIP works
Why an ordinary GPS is several metres off, how a base station and NTRIP bring that down to 1–2 cm, and what you need to get started.
Saurus Group
An ordinary GNSS receiver in a phone or a tractor knows its position with an error of several metres. That is enough to navigate a car, but not for sowing, staking out a building or mapping with a drone. RTK solves exactly this problem.
Where the error comes from
The signal from the satellites passes through the ionosphere and troposphere, and the satellites’ clocks and orbits are not perfectly accurate. The receiver cannot tell these errors apart from its actual position on its own.
What a base station does
A base station is a GNSS receiver placed on a point whose coordinates are known to the millimetre. Because it knows where it is, it calculates every second how far the signal deviates and broadcasts those differences as corrections in the standard RTCM 3 format.
Where NTRIP fits in
NTRIP (Networked Transport of RTCM via Internet Protocol) is the protocol that carries corrections over the internet, usually over a mobile network. The receiver connects to an NTRIP caster or gateway with a username, a password and a mountpoint, and then receives corrections in real time.
RTK FIX and RTK FLOAT
- RTK FIX – the receiver has resolved the whole number of wavelengths; the accuracy is 1–2 cm.
- RTK FLOAT – corrections are arriving, but the solution is not fixed yet; the accuracy is at decimetre level.
FIX is reached within a few seconds to a minute under open sky. The closer the base station, the more stable the solution – which is why networks have several base stations.
What you need
- A receiver or terminal that supports RTK and NTRIP.
- An internet connection in the field (a SIM card in the receiver or a phone as a hotspot).
- An account on an RTK network.
On RTK.ba the AUTO mountpoint picks the nearest healthy base station for your position by itself. Read more on the RTK and GNSS solutions page.