Overview
In this article, we will discuss RTK and how it integrates with some of the latest drone technology and how it can revolutionise the way you collect data in the field.
One of the most popular drones fitted with RTK is the DJI M300 which works seamlessly with Hammer Missions
So, what is RTK, and how will it help achieve highly accurate flight data...?
What is RTK?
RTK stands for Real-Time Kinematic and is a technique used to increase the accuracy of GNSS (global navigation satellite system) positions using a fixed base station that remotely sends out data to a moving receiver.
Traditional GNSS receivers, like the ones in your phone or tablet, usually only give accuracy up to 2 to 4 meters or 7 to 13 feet.
With the addition of an RTK unit and base station, this accuracy can be pushed down to mere centimeters.
When used alongside the DJI D-RTK2 Mobile Base Station the accuracy level is unsurpassed and will give you centimetre-level accuracy.
This is achieved by GNSS data not only being received by the drone but also by the additional base station that sends correctional information to the drone base station (controller) increasing the accuracy of the data.
It's important to understand that RTK is an accuracy enhancing measure as opposed to a signal boosting measure! So if you are struggling to get GPS signal in a congested area with buildings or underneath a structure, RTK alone will not help in strengthening the core GPS signal. It will however help in improving the geotags in your images in case you do have signal so that you have more accurate post processing of your data.
DJI M3E | M30 | M300 RTK Modes
As explained earlier in the post there are several ways to collect data using RTK and is dependent on how accurate you require the data to be.
Base Station Mode
As discussed above in What is RTK, using a base station can significantly increase the accuracy of the data collection so what is a base station and why is it important?
One of the most popular base stations to use alongside the M300 is the DJI D-RTK2 Mobile Base Station
Picture courtesy of University of Edinborough
What is a Base Station
A base station is a high-precision GNSS receiver that supports all major global satellite navigation systems, providing real-time differential corrections that generate centimeter-level positioning data for improved relative accuracy.
Base Stations should be placed on a known point, these known points refer to a previously designated point that has been measured using surveying equipment. These known points are marked with GCPs (Ground Control Points)
The RTK connection between the chosen base station and the M300 allows for the creation of a very accurate geotag to be attached to the images during flight.
How to Connect to a Base Station
Connecting the base station to achieve the high data output is a fairly simplified task. You have to connect the controller to the base station via the Ground Station RTK app included on the M300's Smart Controller Enterprise.
Set up the mobile base station over the already defined known point and input the coordinates into the base station position in the flight app.
Alternatively, you can use a Base Station without having a known point marked by a GCP. The relative accuracy will be similar to that of using a GCP or known point but the coordinate accuracy will be lower. For this method, it is recommended that you leave the base station in its set position for as long as possible to give it time to determine its position.
Pros and Cons of using a Base Station
Using a Base Station in the field has its advantages when it comes to collecting highly accurate data, including centimeter accuracy and precise geo-tagged imagery but there are some factors to consider. Base stations are bulky and could be a hindrance on sites that are not easily accessible and carrying more equipment means more time setting up on-site and then de-camping that equipment when you have finished.
Custom Network RTK Mode
We have already talked about how you would use a base station in the field alongside the DJI M300 but how would you operate if no base station was available or there were no known points?
The M300 custom network RTK mode was designed to overcome these issues...
What is a Custom RTK Network
As opposed to using base stations to accurately measure, the custom RTK network setting uses mobile data from the internet to measure the accuracy, therefore, mitigating the need for additional base stations. These custom RTK Networks will require a license to take full advantage of this feature and can work alongside GCP's for greater accuracy.
Connecting to a Custom RTK Network
As the custom RTK network uses an internet connection to acquire its data it is imperative that the site has an adequate mobile data or wifi signal.
You can use your phone or tablet as a mobile hotspot and connect it to the Smart Controller Enterprise to gain access to the internet. Once this has been done you can open the Hammer App on your phone or tablet and utilise the RTK feature built into the Hammer App
Where to Purchase an RTK License
As discussed earlier in the post, you will need to obtain an RTK license to fully appreciate the ability to be able to use a Custom RTK Network.
These licenses can be obtained from various resellers, a selection of which are listed below:
Pros and Cons of a Custom RTK network
Although Custom RTK has its advantages, mainly being that you do not have to carry additional kit to site it does have its issues. As the custom RTK network relies on a data feed you have to make sure that there is an adequate network connection at all times and that signal will not be lost as this will impact your data collection. Alongside that is the price of the license and possible subscription charges if you wish to use custom RTK as a long-term method of data collection.
How To Use RTK Effectively
As we have discussed, RTK is a very accurate way of obtaining high-quality data no matter what method you use, be it with base stations or a custom RTK network but there are ways to refine the effectiveness of RTK to mitigate risks to your data collection and further enhance the way that data is collected.
1. GCP's
We have mentioned the use of GCP's quite extensively in this post and we would recommend the use of GCP's in conjunction with RTK so that you have a failover in case of loss of RTK signal. This way there is still a method to measure the data correctly but please keep in mind that it will not be as accurate.
For further information on GCP's and their use in the drone industry please see our post How to Collect High Quality Data for Photogrammetry
2. Lever Arm Correction
Lever arm correction or lever arm offset, as it is also known, is the distance measured between the RTK unit and the centre of the camera and if not correctly configured can have a dramatic effect on data collection. If the offset is not set up correctly it could cause issues with the accuracy of geotagging on images.
3. RTK and Flight App
Last but not the least, it's important that your flight app or capture method supports RTK correctly.
Here at Hammer Missions, we cater for a host of mission types and include the ability to use RTK in our mission planning.
Hammer Missions integrates with not only the DJI M300 RTK but the DJI Phantom 4 RTK through the use of the Custom Network RTK feature. Both of these drones are DJI's flagship RTK drones used for highly accurate data collection.
The DJI M300RTK is able to achieve down to 1cm accuracy whereas the smaller more portable DJI Phantom 4 RTK is able to achieve down to 3cm accuracy.
For further information please see How to Set Up RTK Using Hammer Missions
Hammer Missions integrates with not only the DJI M300 RTK but the DJI Phantom 4 RTK through the use of the Custom Network RTK feature.
Conclusion
We hope this blog post helps you understand how to Achieve Highly Accurate Flights with the DJI M300 RTK.
If you'd like to learn more about how to high-quality data and get the most out of your drone missions, please feel free to visit our learning resources.
If you haven't got a Hammer account as yet and would like to try Hammer Missions you can get started on our free trial.
To learn more about our enterprise solutions, including mission collaboration, data processing, and AI solutions, please contact us at team@hammermissions.com.
We look forward to hearing from you.
— The Hammer Team