Setting up RTK: correction data, Fix and quick help.

RTK (Real Time Kinematic) improves the drone’s position from one to three metres down to 2 to 4 cm. Whether your job needs it is covered in How accurate will my model be?. This article is about getting it to work.

Airclip Cloud needs no extra step for it: you upload your photos as usual, and the georeference comes from the RTK metadata in the images.

Which drones have RTK?

RTK comes with DJI’s Enterprise drones, currently for example the Matrice 4E, Matrice 4T, the Mavic 3 Enterprise series, Matrice 350 RTK and Matrice 400. On the newer models the module is built in, recognisable by the distinctive cover. Retrofitting is only possible on the Mavic 3E, 3T and 3M, where it is a separate module. The DJI Mini, Air and regular Mavic do not support RTK. All models compared: Which drone can do what?

The survey models carry an E or D in their name (Mavic 3E, Matrice 4E, Matrice 4D): a high-resolution camera with mechanical shutter and Time Sync. The T variants carry a thermal camera and in exchange a smaller visual camera without Time Sync. They still have RTK so that the frame stays put during inspections at high zoom.

Where the correction data comes from

You switch RTK on in the DJI Pilot 2 app, in the drone’s system settings (“Aircraft RTK”). That is also where you choose the source of the correction data. There are two ways.

Network RTK over the internet. Most pilots fly this way today, in Germany usually with SAPOS, the positioning service of the German state survey offices. You register and receive the server address (NTRIP), port, mount point, user name and password by email. In the app you choose “Custom network RTK” and create a configuration with them. SAPOS is run per federal state: nationwide access costs €100 once plus €10 a month, individual states are often cheaper, and some open-data states are free. Other services such as Trimble VRS Now or Leica SmartNet work the same way. Several providers, or separate accounts for individual states, can be saved as separate configurations; you pick the right one for where you are flying.

For this the remote controller needs internet throughout the flight, via your smartphone’s hotspot or a SIM card in the DJI Cellular Dongle.

Your own base station. Without internet on site, you set up your own reference station, for example the DJI D-RTK 3 for around €1,500. It stands on a tripod, generates the correction data itself and sends it by radio via the remote controller to the drone. In the app you select “D-RTK base station”.

Instead of the D-RTK 3 you can also use a GNSS receiver such as the Emlid RS3. It connects to the remote controller over Wi-Fi and is set up in the Emlid Flow app. How that works with the Matrice 4 is shown in the Emlid RS3 video (in German).

RTK Fix and Float

Before the position is really accurate to the centimetre, the drone has to reach an RTK Fix: an unambiguous solution from satellite and correction data. While it is still calculating without a clear result, it shows RTK Float. For any survey: only take off once Fix is shown.

For plain photo and video flights you can switch RTK off. It adds nothing there, and take-off takes longer because the drone first waits for the Fix.

Getting a Fix

If the Fix takes a while, it almost always comes down to one of these points, and all of them can be solved on site.

No clear view of the sky. Under trees and right next to buildings the signal drops quickly. Walls also bounce the signal back (multipath), and the drone then calculates with the wrong path length. Look for a take-off spot with a clear 90° cone above it. The same applies to the base station.

• Check the internet. With SAPOS and similar services, always first: open the browser on the remote controller and load any page. With a SIM card the PIN must be disabled, most controllers cannot ask for it.
• Check the credentials. One of the most common errors, because there is no message like “wrong password”. The connection simply does not come up. Compare server, port, mount point, user name and password character by character.
• Move. Sometimes it works a few metres further on.
• Switch RTK on in the air. No Fix on the ground? Turn “Aircraft RTK” off, wait for a valid GNSS signal (green indicator top left), take off manually, climb above the roof edge or tree line and activate RTK there.

And if nothing works, PPK (Post Processing Kinematic) helps. All DJI Enterprise drones except the M3T and M30 store the raw satellite data (files with extensions such as .NAV and .OBS). Together with a RINEX correction file you compute the positions afterwards, for example in DJI Terra, REDTOOLBOX or RTKLIB. The result is even slightly more accurate than RTK but costs an extra step. An RTK module still has to be on board.