Do you need GCPs with the P4 RTK?

The DJI Phantom 4 RTK has become drone of choice when it comes to accurate survey. However, within the survey industry there is mixed opinion as to whether or not the advent of RTK drones dispenses with the need for Ground Control Points (GCP).

In most cases, the accuracies that can be achieved without any GCPs or the D-RTK 2 mobile station are less than 3.5 centimetres. For a significant number of projects this would be accurate enough. When in need of higher accuracies, the RTK flight positions are a good photogrammetric support of a well distributed network of GCPs. For the purposes of this blog, we are setting aside the D-RTK 2 mobile station for a future article.

Our Phantom 4 RTK has few limitations but the incorporated one-inch sensor with a pixel size of 0.00241 millimetres (2.41 microns) restricts performance in low-light conditions. The camera can only compensate by increasing the ISO value, which makes the photos grainier and noisier which increases noise in the output point cloud. To some degree, flying missions at a lower altitude compensates for this and can also increase the precision of the alignment of the images.

Having accurate RTK based flight positions does help with creating precision 2D and 3D models with less GCPs, it is still crucial to incorporate a number of CGPs across the project footprint to corroborate the validity of the output. Without any CGPs it is not possible to detect any human or computer inaccuracies that could have occurred at any point in the workflow.

If you need that extra accuracy, beyond the 3.5-centimetre mark, then GCPs will ensure the highest accuracies and best end results.