Airborne RTK for land surveyors has been a technology with an enormous amount of promise for quite a few years now, but was being held back by extremely expensive, complicated, and unreliable technology. However, with the recent announcement of the DJI Phantom 4 RTK, it seems as if this is about to change. Overall, the Phantom 4 RTK is a great piece of technology that will improve both accuracy and efficiency for most surveyors, but it is not a magic bullet. Good operations are required both in the field and in post-processing the data.
Pros:
There are two major benefits to the Phantom 4 RTK over all other DJI drones: accuracy and efficiency.
By adding a dual-band GPS system, with a highly precise clock and camera/gimbal synchronization system, this aircraft can calculate the position of the camera sensor to an accuracy of around 1.5cm in perfect conditions. These specs are great on paper, but what really matters is not the accuracy of the camera, but the accuracy of the final CAD data that comes out at the end of the process. Once all of the noise of the real world is taken into account, the final accuracy that can be expected out of this system is still right around 0.1’. But the big difference is, that it can achieve this 0.1’ accuracy with fewer ground control points than previous system.
That leads to the second major benefit, efficiency. In the past, to do a drone-based topographic survey on 100 acres of land would have taken about 20 ground control points*. With the RTK system, you can get the same level of accuracy, while setting only 5 ground control points, which means less time in the field. And yes, even with RTK, you still need to have ground control on EVERY project that you plan on using for surveying. However, you can get away with a lot fewer.
*Assuming 200’ flight altitude and 0.2’ required vertical RMSE accuracy.
Cons:
The Phantom 4 RTK is not a magic bullet. The system is considerably more complicated than a standard drone surveying workflow, and that complexity means that it requires more training, and creates more room for error. The precise workflow to get good, reliable data out of an RTK system like this involves three steps:
Gather the right data
Process your GPS data
Integrate into Photogrammetry
Gathering the right data is probably the simplest of the steps, but still needs to be done correctly. Both the drone and the accompanying GPS ground station need to be set up correctly, and set to gather the right data. Not to mention all of the mundane things like making sure all of your equipment is in the right place and charged when you need it.
Once all the data is collected, the raw GPS data needs to be processed into the coordinates where the photos were taken. This means performing either RTK or PPK corrections on the raw satellite data. Then, there is the very, very messy process of ensuring that all of your ground data is in the exact same datum & coordinate system as the airborne RTK. This is where we have seen the most issues with RTK systems in the past.
Once your GPS data is processed accurately, it needs to be worked correctly into the photogrammetry model. Even if the camera position data is perfect, mistakes in the rest of the photogrammetry process can lead to errors in the ground model. This is something that typically requires a trained photogrammetrist, as there are a lot of complications in the photogrammetry process that can lead to bad data.
Creating a Solution:
While the RTK workflow may sound intimidating, it is something that can definitely be conquered by having the right workflows and working with the right professionals. Aerotas has been developing high-accuracy drone workflows since 2014, and our training workflows for the Phantom 4 RTK will ensure best-in-class accuracy out of this complex, but extremely promising system.
Interested in pricing or learning if the Phantom 4 RTK is right for you? Contact us below to find out more.