Fundamentals of Positioning Accuracy in Aerial Photography

Introduction to RTK, PPK and Cloud PPK technologies

In geodesy and cartography, aerial photography has been used for a long time and quite widely. However, the emergence of unmanned technologies has made it possible to increase not only the accuracy and efficiency, but also the availability of shooting. At the same time, it should be understood that unmanned solutions still have their own specifics, and operators and a team of specialists on the ground need to consider a number of factors in order to choose the best solution for the job. Depending on the accuracy of the results required for the mission, as well as time constraints, users can improve positioning accuracy by relying on ground control points (GCPs) and a non-RTK drone or a real-time RTK-enabled drone solution. post-processing and fixes.

Technologies that improve positioning accuracy

Real Time Kinematics (RTK)

RTK Application Diagram with DJI Phantom 4 RTK Drones
RTK Application Diagram with DJI Phantom 4 RTK Drones.
Explanations for the scheme:
Satellite – satellite,
Base Station – base station,
Drone – DJI Phantom 4 RTK quadcopter.
Controller – remote control

Real-time kinematics (RTK) is an advanced satellite positioning technology that includes a ground station with a known position as an auxiliary position reference to provide more accurate data. When an RTK system is installed on an aircraft, it is used to combine and correlate location data received from virtual and physical base stations with real-time correction of the aircraft’s camera position. When properly deployed, drones can create centimeter-level accurate location data that are embedded in aerial photographs in flight.

Unmanned RTK solutions are especially in demand as they provide real-time results. But for the qualitative performance of tasks, constant and good communication is necessary throughout the entire flight mission. Meanwhile, specialists often have to work in conditions where stable data transfer is difficult.

In flight, RTK requires two types of data links, one between the remote controller and the RTK base station, and the other between the remote controller and the aircraft. The communication line between the remote controller may encounter instability during network connection, while the communication between the remote controller and the drone may be affected by obstacles and interference in the flying area. Therefore, to reduce the risk of loss of communication on data links, PPK technology can be a good alternative for geodetic surveys, especially if you plan to work in remote areas with poor network quality or obstacles such as trees, buildings or metal structures.

PPK technology

Scheme for the use of PPK technologies, including technology based on a cloud service.
Scheme for the use of PPK technologies, including technology based on a cloud service.
Explanations for the scheme:

Satellite – satellite,
Base Station & Drone is a DJI Phantom 4 RTK base station and quadcopter.
Cloud Server – cloud server
Controller – remote control
POS data – POS data

PPK allows you to correct the data not during the flight, but immediately after it. The data itself is usually stored on board the drone. After the flight is completed, the specialists combine this data with the data of the base station, receiving it in special software installed on the PC. This gives users more flexibility and reliability: for example, if there are problems on the real-time data link in flight, the accuracy of the results can still be maintained because the calculations include PPK data. The take-off location does not have to be ideal, and the distance from the base station may be longer.

The new cloud service PPK (Cloud PPK) for DJI Phantom 4 RTK takes efficiency to a new level by making computing operations performed right in the remote control. This became possible after the introduction of an additional option in the DJI GS RTK flight planning application. This solution allows you to stop using a separate application on a desktop computer or laptop. Data collected from any DJI RINEX Base Station can be quickly processed within the app, streamlining workflows without compromising data accuracy. The received POS data can be easily imported into DJI Terra for further processing.

Differences between RTK, PPK and cloud PPK technologies:

Drone + RTK Drone + RTK + PPK Drone + RTK + Cloud PPK
Positioning accuracy centimeter level centimeter level centimeter level
Requires connection to real-time data Yes No No
When and where are the calculations performed? Real time during drone flight After flying in PPK software After flying in the GS RTK app on a compatible remote control
Impact of losing RTK Lock High.Connectivity may vary depending on internet or local data connection. Low Low
RTK base station required Yes. Requires connection to base station or network RTK like CORS Yes. Requires connection to base station or network RTK like CORS Yes. Requires connection to base station or network RTK like CORS

The table clearly shows that all RTK and PPK unmanned solutions are capable of providing centimeter-level accurate data. But RTK solutions require a base station and special conditions for takeoff and flight in order to process the data in real time. At the same time, PPK-based solutions offer more flexibility. Regardless of where and how experts have used unmanned systems to perform geodetic surveys, all tasks will be completed, and the data will be accurate and reliable.

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