Do you need the DJI Base Station?
Why you want to use the DJI D-RTK 2 base station to stream RTK correction information directly to the aircraft.
Summary
Aerotas strongly recommends using the DJI D-RTK 2 base station, as integrating 3rd party hardware creates a complicated and error-prone workflow.
There are numerous ways to process GNSS data from the DJI M300 RTK and the Phantom 4 RTK. This article will discuss the five most common methods for processing data from DJI RTK drones and weigh their strengths and weaknesses. Let us start by making something clear; there is no single “perfect” method for processing GNSS data. Every method has its pros and cons, and the right solution for one surveyor might not be the right solution for all. Some surveyors are more comfortable with WAN network troubleshooting than others, and that can influence your preferred method for processing your data.
Aerotas has processed thousands of flights from DJI RTK drones. Our recommendation for the vast majority of surveyors is clear - we recommend using the DJI D-RTK 2 base station for live RTK corrections. Aerotas suggests this workflow because it is both reliable and straightforward to use. If anyone is on the fence, we strongly recommend buying the D-RTK 2 base station along with your DJI drone.
Factors we consider
We considered three primary factors in analyzing the different GNSS processing methodologies and ranked each methodology on a scale from 1 to 5 (5 being best).
Accuracy: Accuracy here refers to how accurate and precise the final data is at the end of all processing, regardless of the complexity of the process. We measure accuracy as the RMSE error of independent checkpoints at the end of a survey.
Reliability: We want to know if this methodology and workflow will work on every project, every time. If a project can’t work on every project, it will rank lower on reliability. If software errors, network errors, or processing errors force a site to be re-flown or re-visited to gather additional data for any reason, it will rank lower on reliability.
Ease of Use: How much training & familiarity with software is required to use this workflow? Do you need a deep understanding of all of the software to get it right? How many steps are necessary to actually set up the equipment in the field and process it correctly?
Detailed Methodologies
D-RTK 2 Base Station
Pros
Extremely simple, single-button integration
Extremely precise results
Highly reliable workflow
Works anywhere - no need for Wi-Fi or cellular connection
Can fall back to PPK corrections if necessary
Cons
You have to own and set up a second base station for most jobs
This method uses the DJI D-RTK 2 base station to stream RTK correction information directly to the aircraft. The setup process is incredibly simple; you just turn the base station on, automatically connecting it to the controller and the aircraft. By using advanced post-processing workflows, you don’t need to set up over a known point or localize to a project site with this base station. The photogrammetrist can handle all of that in the data processing stage. Aerotas has written more about this workflow here.
This workflow’s primary benefit is that it is very easy to set up and rarely has any significant failure that would require a field revisit. If the base station or RTK signal were to fail, the drone notifies you immediately. Even if the RTK connection were to fail, PPK processing is still possible in post-processing. Further, this workflow does not require any internet connectivity to work. Surveyors get high-quality accuracy on all sites regardless of the location or cellular service coverage.
The only real downside to this method is that you have to own and operate the D-RTK 2 base station. For some surveyors, this means that you have to bring and set up two base stations on a single job, this one and your actual base station from Trimble, Leica, Topcon, etc. While this is a real pain point, the benefits of the D-RTK 2 workflow (simplicity & reliability) far outweigh the cost of setting up the DJI base.
3rd Party Base - NTRIP Connection
Pros
Utilizes existing equipment
Extremely precise results
Cons
Highly complicated and error-prone workflow
Requires in-field software manipulation
Requires deep familiarity with current GNSS hardware
This methodology uses a 3rd party base station, like those made by Trimble, Leica, Topcon, or others, to stream RTK correction information directly to the aircraft. It does this by utilizing an internet transfer protocol known as “NTRIP.” In short, you configure your base station to broadcast its correction data live to the aircraft through this protocol. From this point, the aircraft calculates the precise camera positioning during the flight.
This setup creates the same very high-quality accuracy and reliability as the D-RTK 2 workflow. If set up correctly, you have live information about the quality of the RTK FIX and can make adjustments in the field if necessary. Additional post-processing methodologies can fine-tune the accuracy and localize the project. It also does not require an internet connection on-site, meaning surveyors can use this method anywhere. Further, it removes the need for a second D-RTK 2 base station, so only a single base station is required.
The problem with this method is the complexity of setting up the NTRIP connection from the base station to the drone. You have to configure your base station to broadcast the correction stream and configure the aircraft to receive it; this is much easier said than done. Every base station will have different procedures, meaning that you can’t easily standardize procedures or troubleshoot errors. Some base stations have guides posted online, like the Trimble R10.
[VIDEO] Setting up a DJI Phantom 4 RTK with a Trimble R10 as the Base Station
But even then, it is a complicated methodology where very small errors can have a significant impact on accuracy. You should only use this methodology if you have a deep familiarity with networking technology, know your base station’s software very well, and are comfortable with highly technical troubleshooting. That said, if you can overcome the technological hurdles, this workflow will provide the same level of accuracy as the D-RTK 2.
3rd Party Base - PPK Processing
Pros
Utilizes existing equipment
No complicated network setups
Cons
Complex and error-prone post-processing workflow
Limited in-field troubleshooting capabilities
Can have unexpected errors and require field-revisits
This methodology uses the same hardware setup as the NTRIP connection methodology but has a different field workflow. Instead of worrying about the troubles of network connections, the surveyor flies the drone without a live RTK connection, with the base station collecting data independently. The base station and the aircraft GNSS data are merged in post-processing using PPK.
Because you are relying on PPK processing only, the setup is extremely simple. Just set your base station to record RINEX data (ideally at a rate of no slower than 1Hz), and then fly the drone normally. This PPK workflow works on all sites because no internet connection is required.
The biggest downside to this methodology is that it is slightly less accurate and not as reliable as using live RTK connections. If there were any errors in collecting data, you wouldn’t be aware of it until back in the office reviewing the data.
Processing PPK data can also result in unexpected noise that you only discover back in the office, resulting in a site revisit. And because you are already using PPK processing, there is no “fall back” processing methodology if there were any satellite errors.
Although this is a straightforward method, it is not our recommended workflow because it has numerous pitfalls that simply don’t exist when using live RTK data.
No Base Station - Network NTRIP Corrections
Pros
Utilizes existing equipment
No base station required at all
Extremely precise results
Cons
Requires active, reliable internet connection
Limited ability to troubleshoot or solve errors in the field
It is possible to get live RTK data over NTRIP without a base station of any kind by using an internet-connected NTRIP stream. This process requires an internet connection on the job site either through local Wi-Fi, a Wi-Fi hotspot, or a dedicated 4G attachment to the controller.
This is a very attractive workflow for users who already subscribe to streaming correction services and have excellent cell coverage over their potential job sites. You can connect to live RTK data over the internet and still fall back to PPK if there are issues on a job site. Modern VRS systems are very accurate, and so the resulting data is usually of very high quality. Another added benefit is that using the NTRIP network workflow requires the least amount of physical equipment on-site.
The biggest downside is the need for an active, reliable internet connection. We have had too much experience working on job sites with either poor or no cell service for us to be able to recommend a solution that relies so heavily on good cell connections. Even when there is a good cell connection, a brief interruption in the internet connection can cause problems. There can also be some difficulties in logging into your network NTRIP connections, which cause some ease of use problems. But, the internet requirement is the most significant pain with this method. However, if all job sites are in highly developed, urban areas, then perhaps this is the right solution.
No Base Station - PPK Only Processing
Pros
No additional equipment required at all
Cons
Significant effort required in post-processing
Can cause errors due to large baseline distances
No ability to troubleshoot errors in the field
If you have an RTK enabled aircraft but no DJI base station, no 3rd party base station, and no access to any network solutions, the only solution left is PPK only processing with publicly available correction data. While this is undoubtedly the cheapest solution out there, it is not the best solution.
Publicly available correction data often suffers from long baseline distances from the job site to the actual base station location, leading to error in your model. Further, these base stations can’t always be monitored remotely and are not 100% reliable, as they often go down unexpectedly. Post-processing data with public base station data is also quite time-consuming. PPK only processing should only be viewed as a last resort when all other GNSS processing methods fail.
Our Recommendation
While the DJI D-RTK 2 base station is far from perfect, it is the best GNSS processing solution for DJI RTK enabled drones.
Aerotas strongly recommends using the DJI D-RTK 2 base station with the Phantom 4 RTK or M300 RTK on projects where accuracy matters.
How the DJI Base Station Works
Surveyors frequently ask how the DJI D-RTK 2 works in terms of its GNSS corrections and calculations and how it can get comparable accuracies to base stations like those from Trimble and Leica at a much lower cost. The short answer is the D-RTK 2 base station is a purpose-built machine that is very good at streaming correction data to DJI drones. Still, it is NOT anywhere near as good as Trimble and Leica base stations for all other applications.
The DJI D-RTK 2 base station’s primary purpose is to stream correction data from the base station to the controller and eventually to the aircraft. RTK calculations are done live on the aircraft, and this calculates extremely precise geolocation. I say precise and not accurate deliberately because the correction methodology ensures that the relative accuracy between the base station and the aircraft is extremely high quality (i.e., high precision). Yet, the absolute geolocation may vary by a few feet (i.e., low accuracy). This can and should be corrected in post-processing by translating different flights or different base station locations to align with one another and then align the project with ground control points present on the ground. It is technologically possible to achieve a comparable result by occupying the base station over a known point. However, the software workflow for this is extremely limited. It only works in WGS84 lat/long and does not support any of the most common coordinate systems that surveyors use in the real world, and therefore would require post-processing corrections anyway.
While the DJI base station is technically capable of performing additional survey-related functions such as acting as a base or rover, we have found that implementation to be extremely subpar. The software is very poorly designed and, aside from streaming corrections to the drone, is very limited in what it can do. The DJI D-RTK 2 runs on proprietary software, so there is no way to enable further functionality in the hardware without DJI’s support, and they have been very slow to add features to the D-RTK 2 base station. Furthermore, the D-RTK 2 tripod hardware and leveling bubbles are not of very high quality. Merely attempting to occupy a known point accurately can be problematic. Thankfully, this issue does not matter if the base station is only relied upon for streaming correction data to the drone. In fact, in our testing, the base station can even be set up at an angle and can still provide accurate relative positioning when an RTK FIX is established with the aircraft.
In conclusion, the D-RTK 2 base station is the perfect tool for streaming live RTK corrections to DJI aircraft but is quite limited in its other capabilities.
If you would like to discuss ways to improve your drone program Aerotas is here to help.
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