Typically, MicaSense cameras rely on the DLS2 to receive standard GPS coordinates for its automatic capture modes and for writing location coordinates to image metadata. These location coordinates are accurate to about 1-2 meters, but the accuracy can decrease as the aircraft flies faster.
Using Real-Time Kinematic positioning (RTK), it is possible to achieve a higher positioning accuracy down to a few centimeters. According to DJI, the M300 RTK can achieve as little as 1cm accuracy (horizontally) when paired with their D-RTK2 mobile station.
This guide will list the prerequisites and necessary steps to achieve RTK precision with MicaSense cameras that have Skyport (PSDK) mounts. If you are unsure whether you have a Skyport or not, please see: Skyport vs Quick Mount Kit
Different ways to use RTK
There are 3 primary ways to utilize RTK positioning. In all 3, the relative accuracy between the drone and base station is very good. However, the accuracy of the position of the base station will impact the accuracy of the images and ultimately the position of the map.
Place base station on any location and fly. In this case the images will only be accurate relative to each other. Image processing will go faster, and the output map will be more precise and self-consistent. When flying in this mode, the base station doesn’t know where it is in any absolute sense, it picks its own position after booting and running for a few minutes. If the station is placed in a different location each time, it won’t be possible to perform repeatable data collections.
Pick a spot in the field. The spot doesn’t have to be surveyed. Always put base station at this spot precisely. You may consider putting a stake in the ground and marking it with a dot so you can put the station on the same location every time. The first time you go to the field, let the station warm for an hour or more. After it is warmed up, write down the coordinates (lat/lon/altitude) where the station thinks it is. Absolutely the location may be 5 meters off, but if you put it in the same location each time, all the maps will be repeatable.
Note: If the DJI system can connect to the internet, the base station may be able to get CORS data, which is reference data from nearby base stations. This will increase accuracy. We have not tested this method.
The most accurate method is to get absolute accuracy by getting a point on your field surveyed and inputting the coordinates the surveyor tells you into the DJI remote as the location of the station. You will put the station on this point every time to get absolute accuracy.
- A compatible DJI drone with RTK support. Currently the only tested model is the M300 RTK. The Phantom 4 RTK and M210 RTK are currently not supported. Make sure it is on the latest firmware on your drone.
- A compatible RTK station. In this guide we are using DJI’s own D-RTK2 mobile station. Refer to DJI documentation for other compatible RTK stations. Make sure it is on the latest firmware. We have only tested using the D-RTK2 mobile station.
- A MicaSense camera with a Skyport (PSDK) mount. This will not work with a “Quick Mount” kit, which only provides power to the camera(s). Note that the Dual Camera System does not have a Skyport mount, so it is not possible to use the Dual Camera System with this guide.
- MicaSense firmware updated to latest version. For RedEdge-MX you must have v7.4.0 or higher. For Altum you must have v2.4.0 or higher.
Before you can fly, you’ll have to do some prep work. Below are the steps we took with our M300 RTK and D-RTK2 station. We strongly recommend setting up your RTK station on a surveyed point so that you have an absolute point of reference. In addition, if you ever plan to fly the same field on multiple days, it is important to place the base station in the same exact location.
- Set up the D-RTK2 station on a repeatable point, as mentioned above. Ideally this would be on top of survey marker. Using the bubble levels on your tripod and/or the RTK station, ensure everything as level as possible while also being stable to not lean or tip over in a wind gust. Best practice is to also ensure there are no obstructions anywhere near the RTK station or you may have trouble getting a fix on the drone. The user guide can be found on DJI’s download center.
- Set up the M300 RTK. Follow DJI’s guidelines on how to set up your drone and perform a preflight checklist. Follow this link to DJI’s downloads page for more information: https://www.dji.com/matrice-300/downloads
- Mount the MicaSense camera. If you have a dual gimbal for the M300, be sure to use Gimbal 1, which is the side towards the drone’s left “wing”.
You will need to also have the DLS2 mount which came with your camera kit. If you do not have a DLS2, you can purchase one by clicking here.
Once the camera is mounted, connect the DLS2 with the included cable. Be sure the cable is secured in such a way that it will not come loose and risk getting caught by the props.
- Verify telemetry on the Web UI. In order to ensure that the camera and drone have synchronized timestamps, we need to check the camera’s web UI. This can be done by via Wi-Fi or ethernet. If you are unsure how to do so, please click here.
In the home/status page, you will see a row called “Time” to show the current timestamp. Note that this is in Universal Time and cannot be changed to your local time zone. What you are looking for is the “P” inside a circle as shown below:
This indicates a “PPS lock”, meaning the precise timestamp of the camera and drone are synchronized. If all other systems show up as green (meaning all telemetry is nominal), then you can proceed to the next step. If you do not have a PPS lock, try rebooting the camera or waiting a few more minutes for the synchronization to complete.
Now that your data contains RTK correction, you can then process your images using photogrammetry software. There are some recommendations on how to process RTK data, which are covered in the processing guide for Agisoft Metashape and Pix4DMapper.