General RTK / PPK Processing
Why use RTK / PPK
RTK (Real Time Kinematic) and PPK (Post Processed Kinematic) are two very similar processes for using detailed satellite observations to document highly accurate locations for the aircraft during drone photogrammetry. Typically, this requires a specialized GPS antenna and receiver on the aircraft itself to receive, store, and compute dual-band satellite data.
RTK and PPK processing can increase the accuracy of a final project, while reducing the number of ground control points required, because the location of the aircraft, and subsequently its camera, is known to a high degree of confidence. Typically, the most significant benefit of using onboard RTK or PPK is the reduction of required ground control points to achieve a certain level of accuracy.
RTK vs PPK difference
RTK and PPK operate on the same basic principles of using GPS signal phase differentials between a base station and a rover to calculate extremely precise location information. The difference between them is that RTK is processed in real-time in the field, while PPK is post-processed in the office.
Real-time processing offers the benefit of quicker access to location data, however it often comes with a more complicated workflow. Real-time processing requires a radio or internet based link from the aircraft to its base station or network of base stations, which can be complicated to set up, unreliable, and expensive.
However, in drone photogrammetry, office processing is required in projects no matter what, so there is minimal benefit to the complicated workflow of RTK processing. For this reason, Aerotas strongly recommends PPK processing, which is a simpler and more robust workflow. In the PPK workflow, raw satellite date is brought back to the office where it is processed into accurate photo image locations.
Accuracy & RTK/PPK
When using on-board RTK/PPK, it is still necessary to perform some measurements on the ground. While a great deal of marketing material published by hardware manufacturers claim that RTK/PPK can provide accuracy without ground data, this does not meet minimum surveying standards or ASPRS positional accuracy standards. At the very least, it is strongly recommended to set a handful of independent checkpoints to verify the accuracy of the project data prior to sealing any survey based on airborne RTK data.