RTK GNSS
RTK (Real Time Kinematics) - technology that allows the increasing accuracy of the GNSS module to a mere few centimetres. SmartAP Autopilots support RTK GNSS based on UBlox NEO M8P modules. This article demonstrates the procedure of setting up the flight with RTK GNSS.
It is assumed that you already have the following equipment:
RTK GNSS module installed on a drone (also called Rover)
RTK GNSS module as a base station with a USB connector
Active patch antenna located on a ground plane (the middle of a car roof is a good example)
Computer with SmartAP GCS installed
Telemetry modules configured and working on both drone and ground station (telemetry is used to transfer corrections from base station module to Rover)
RTK GNSS is very sensitive and needs to be set up with care
The base station antenna position should be fixed at all times. Please make sure that it is not able to move and has a clear view of the sky far enough from surrounding buildings. Essentially, ensure it is not shadowed by obstacles. A tripod or a car roof are good locations for the base station antenna.
Once you have located the antenna, connect the SMA cable to the ground module and plug the module into the USB port on your computer.
Solid green LED - Power is on and module is working
Blinking blue LED - GNSS module has 3D position fixed
First things first, open SmartAP GCS and connect it to the drone. Then go to the RTK tab at the bottom part of the Main Window. Choose the COM port of the GNSS module and press the Connect button. Once you're connected you'll be able to see the status of the base station module.
Once the base station has enough visible satellites, as long as solid 3D fix and position deviation is not high, you can start the Survey-In procedure by pressing the Start Survey-In button. This procedure determines the accurate position of the base station based on the measurements. By default, it’s set to run for at least 3 minutes, and the accuracy deviation should be less than 1 meter. Note that longer measurements and smaller deviations will increase the accuracy of readings sent to the Rover. The measured accuracy and progress are shown on-screen. This process may take a few minutes.
3D Accuracy - Positioning accuracy estimation for the last measurement (single measurement) Mean 3D STD - Standard deviation of the accuracy after Survey-In process has begun
After the Survey-In process is completed SmartAP GCS will start sending corrections to the Rover. Survey-In status will change from In Progress to Completed.
If you take a look at the GNSS status of the vehicle shown on the top panel, you'll notice the change from GNSS to D-GNSS meaning that the Rover module is receiving readings. The D-GNSS mode becomes active after a few seconds as the base station module starts sending corrections.
RTK has two modes: Float and Fixed. Float mode is easier to reach as it usually becomes available in 30-60 seconds after D-GNSS mode is active, however, it's less accurate. Later, the system will automatically go to Fixed where the accuracy will be higher but the process may take a little longer to complete.
What will happen if the Rover looses connection with the base station?
The drone will continue flying. It is likely to do so with slightly less accuracy, however, if the connection has not been regained in 60 seconds, the GNSS module will go into regular mode. Once the connection has been re-established, the system will automatically go back into RTK mode.