What RTK actually does
A standard GNSS receiver on a drone knows its position to within a few metres. RTK (Real-Time Kinematic) adds correction data from a base station or a reference network, so the position of the drone at the moment of each photo is known to centimetre level.
Without RTK the photos are only roughly positioned, and the processing software has to be anchored with a large number of ground control points that someone must place and measure on site.
Where the 1–2 cm figure comes from
The figure describes positioning under good conditions with a fixed RTK solution. The accuracy of the finished map or model also depends on several other factors.
- Flight height and camera resolution (ground sample distance)
- Image overlap and flight pattern
- Terrain, vegetation and lighting
- Quality of processing and the coordinate system used
Why checkpoints still matter
RTK reduces the number of ground control points, but it does not replace independent verification. We measure checkpoints that are not used in processing and compare them with the finished model. The result is reported as an error value in plan and in height.
Ask for a checkpoint report, not just a number from a brochure. A stated accuracy is only meaningful when it has been measured.
What to ask your contractor
- Which RTK source is used, and was the FIX solution held throughout the flight?
- Are independent checkpoints reported, with errors in plan and in height?
- In which coordinate and height system are the data delivered?
- At what ground resolution is the survey flown?