What is real-time kinematics and what does it mean for your drone
How accurate is enough? If you're like most surveyors, the answer is "as much as possible."
With an RTK drone, surveyors and other types of corporate drone pilots can expect centimeter-level positioning accuracy with every flight. The system is a marked improvement over satellite data alone and can help ensure you have the accurate information you need to do the job.
What exactly is RTK?
Real Time Kinematics, or RTK for short, is a special technique for satellite positioning that can produce centimeter-accurate results, making it a valuable tool for surveyors around the world. The method involves measuring satellite data against a ground station to obtain precise, real-time information.
Key parts of the RTK technique include:
- A base station : The base station, also known as a reference station, remains at a defined point on the ground, where its GPS position is continuously compared with the position of a drone. To function properly, an RTK drone must remain in constant connection with the base station.
- RTK Receiver : This device is part of the drone's hardware and sends signals to both the controller and a satellite.
- Controller : Your drone's remote controller sends signals to move the drone and displays changes in coordinates.
- Satellite : Satellite data is still a critical part of any RTK system. However, instead of simply communicating with the drone's receiver, the information is also tested against the base station, establishing the accuracy of the location.
The RTK advantage
RTK data is far superior to satellite data alone, because it can be used to correct for inaccuracies and discrepancies, ensuring the information comes as close to reality as possible. There are numerous factors that can distort satellite coordinates, including incremental weather, tall buildings, mountains, and other issues that require RTK correction. These are called “tropospheric delays”. The RTK system fills these gaps with real-time data from the base station and drone.
The main advantages of an RTK system include:
- Greater Accuracy : This is the biggest one. Compared to satellite data alone, an RTK system offers high accuracy – typically down to the centimeter level.
- Real-time corrections : While other adjustment technologies like PPK (more on that later) correct skewed data and fill in gaps at the end of a flight, RTK corrections correct errors automatically. This means that the data you see during a flight is data you can trust.
- Fewer Ground Control Points : Ground control points are fixed points on the ground with known coordinates that can be used to readjust GPS data. Arranging and measuring these points can be time consuming. However, with RTK, the base station makes GCPs irrelevant, allowing you to complete projects with much less hassle.
The difference between similar drones with and without RTK is striking. In a recent study, DJI and DroneDeploy compared the Phantom 4 RTK and the Phantom 4 Pro (a consumer edition that does not have a built-in RTK receiver) on more than 30 different flights with a checkpoint system for a roof of a building. The results showed that the RTK-enabled drone better calculated the horizontal and vertical precision of the measured points, as well as the precision of linear measurements.
Using an RTK drone with PPK
While RTK technology is a big step forward from using satellite data alone (especially if it isn't corrected with ground control points), it does have some limitations. For example, if your drone loses connection with the controller or satellite, then real-time data transmission will not be possible. Some jobs, especially longer ones in difficult terrain, make it difficult or even impossible to maintain stable data transmission.
As a result, the RTK system is not the only way surveyors and other drone professionals correct satellite coordinates and ensure accuracy. Another method is called “post-processing kinematics”, or PPK for short. Although they are often talked about together, it is important to note that RTK and PPK technology are actually very different.
PPK essentially requires the same equipment as RTK, but is done with a completely different workflow. Unlike RTK, a PPK workflow means you won't need real-time corrections. Rather, the drone system stores data on board the drone, and post-flight calculations combine both drone and base station data, producing the results in PPK software on a computer. The data is created with geotagged coordinates from an onboard GPS unit. Your base station, meanwhile, will also keep track of the drone's location information. These numbers can then be compared to each other after the completion of a flight.
While you don't get the convenience of fixes on the go, a PPK system requires fewer transmissions and so can get the job done even with poor network signal reception or other obstructions. To maximize the potential and cover the limitations of each method, many top-tier enterprise drone solutions use both RTK and PPK technologies to ensure the most accurate positioning possible. The Cloud PPK service for DJI's Phantom 4 RTK, for example, can be used to conduct calculations on the drone's remote controller, in addition to the DJI GS RTK flight planning app. This setup also means you can tailor the Phantom 4 RTK to the workflow that makes the most sense.
The resulting data can be quickly imported into DJI's advanced mapping software, DJI Terra, for further analysis.
Getting the most out of your RTK hardware
If you're looking for a reliable RTK system for every flight, you'll want a corporate drone from DJI. Our RTK systems use an on-drone module and a high-precision GNSS mobile station. The combination of onboard RTK receiver and GNSS signal reference station offers a high degree of RTK accuracy. Whether you choose to rely completely on RTK or also have PPK capabilities as a backup, using a DJI drone means you can expect to stay connected regardless of the mission.
Some of DJI's top RTK drones include:
The Phantom 4 RTK
The perfect drone for entry-level surveys is here. Thanks to its RTK module, this business drone offers a horizontal positioning accuracy of 1 cm + 1 ppm, a vertical positioning accuracy of 1.5 cm + 1 ppm and an absolute horizontal accuracy of photogrammetric models within 5 cm. The drone also stores satellite observation data to use for PPK with the DJI Cloud PPK Service.
Matrix 300 RTK
Welcome to the future of commercial drones. The Matrice 300 RTK accentuates its advanced RTK positioning system with advanced AI capabilities and six directional sensing positionings. Add a maximum flight time of 55 minutes, hot-swappable batteries, and a wide-range operating temperature, and you get a drone that's ready for any job.
Matrix 30
The Matrice 30 takes everything the Matrice 300 has, and packs it into a portable package. With a smaller footprint and weight, the Matrice 30 is much easier to take along on inspection missions. With integrated RTK modules, it is the perfect solution if you need to conduct precise drone inspections of assets or infrastructure that require centimeter-level accuracy.
Mavic 2 Enterprise Advanced
This compact and foldable tool is equipped with a dual 48MP integrated sensor with a thermal resolution of 640x512 px. Its attachable RTK module allows this drone to carry out precise and repeatable inspection missions. With a flight time of up to 31 minutes, this is a powerful and portable solution.