This technique is one of the most commonly used where the operator sets the base station up, turns it on, and via the DJI Pilot App, commences flying as soon as the base station status changes to ‘Connected’.

As detailed in the technical specifications for the base station, the positional accuracy for a single point is as follows:

Horizontal：1.5 m(RMS)
Vertical：3.0 m(RMS)

The base station serves as the main reference point for the drone. Coordinates collected by the drone are always accurate relative to the base, but may not be accurate relative to the selected coordinate system (EPSG). This is called relative positioning and occurs when the position of the base station is not accurately defined in the selected reference frame (EPSG).

This means that whilst the relative accuracy (the position of the drone relative to the base station) will be 1 – 2 cm, there will be large errors for the absolute accuracy, because the base station was not accurately geolocated. There will be a horizontal error of at least 1.5m and 3m vertically. This can be a problem should multiple flights need to be carried out of the same area over a period of months/years and you are wanting to compare the flights to each other. For example if you want to compare the ground level in one flight to another, which was carried out on a different day.

It will also cause problems if you're flying over a large area, involving multiple flights and keep moving the base station, but want the flights to be merged to create one data set.

Therefore, if you want to use the D-RTK 2 or D-RTK 3 base station for RTK flights, it is essential that it is setup over a known point, accurately surveyed in to WGS 84 (EPSG 4326), with these coordinates entered into the base station on start up (see section below).

Failure to do this will result in the base station attempting to calculate its location using the satellites and as noted above, this will result in large positional errors and your resulting drone flight will not have have absolute accuracy.

The DJI D-RTK 3 base station is often misunderstood when it comes to its absolute accuracy capabilities. While it can deliver centimeter-level relative positioning to a connected drone, this does not mean it achieves centimeter-level absolute positioning by simply powering it on. In stand-alone (uncalibrated) mode, the base station’s absolute accuracy is limited to about 1.5 m horizontally and 3.0 m vertically (RMS), as stated in DJI’s own specifications. This means that although the drone will fly with high precision relative to the base, the entire system could still be offset by several meters in absolute terms.

The specifications further show that using satellite-based differential corrections (without a surveyed location or network RTK) improves accuracy to 30 cm horizontal and 40 cm vertical after a 20-minute convergence period. However, this is still far from the 1 cm accuracy many users expect.

The only way to achieve the advertised 1 cm (horizontal) / 3 cm (vertical) + 1 ppm accuracy is by using Network RTK Calibration, which relies on receiving RTCM correction data via a network connection (e.g., NTRIP) or by inputting known surveyed coordinates. Leaving the base running for several hours will not significantly improve its absolute position, as it does not perform long-term PPP (Precise Point Positioning) or automatic self-survey.

In short, the D-RTK 3 provides excellent relative accuracy out-of-the-box, but achieving true centimeter-level absolute accuracy requires either a network RTK connection or use of surveyed coordinates for the base station.

If known points have been set out and surveyed in using survey grade equipment, then you can enter the coordinate of the known point into the control under the Advanced Settings of the D-RTK 2 base station.

As shown below, go into the Advanced Settings -> Adjust Coordinates.

You can now enter the coordinates of the known point that the base station is setup on. Click OK and you are ready to continue you flight preparation.

For other models of base station, please refer to the manufacturer's instruction manual on how to enter or adjust the coordinates of the base station.

Using an NTRIP provider will provide real time RTK corrections via the internet directly to the controller of the drone, without the need for a base station. This will use a virtual base station relative to WGS 84 and therefore will not only provide high relative accuracy, but also high absolute accuracy.

There can be subscriptions costs associated with this and the operator needs to ensure a stable internet connection to obtain the corrections. If the NTRIP link goes down, then the RTK corrections will be lost.