Flying with RTK GNSS

RTK (Real Time Kinematics) - technology which allows increasing GNSS module accuracy to just a few centimeters. SmartAP Autopilots support RTK GNSS based on UBlox NEO M8P modules. This description demonstrates the procedure of setting up the flight with RTK GNSS.

It's 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 USB connector
  • Active patch antenna located on a ground plane (the middle of a car roof is a good choice)
  • Computer with installed SmartAP GCS
  • Telemetry modules configured and working on both drone and ground station (telemetry is used to transfer corrections from Base Station module to Rover)

Locating the antenna

RTK GNSS is very sensitive and needs to be set up carefully.

The base station antenna position should be fixed all time. Please, make sure that it's not moving and has a clear view of the sky far enough from the buildings and not shadowed by the obstacles. Tripod or a car roof are good locations for base station antenna.

Once you have located the antenna, connect SMA cable to the ground module and plug the module into USB port of the computer.

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Solid green LED - Power is on and module is working
Blinking blue LED - GNSS module has 3D position fixed

Connecting in SmartAP GCS

First of all open SmartAP GCS and connect to the drone. Then go to RTK tab in bottom part of the Main Window. Choose the COM port of GNSS module and press Connect button. Once you're connected you'll see the status of the base station module.

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Starting Survey-In

Once the base station has enough satellites visible, solid 3D fix and position deviation is not high you can start Survey-In procedure by pressing 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 at least 3 minutes and the accuracy deviation should be less than 1 meter. It's obvious that longer measurements and smaller deviation will increase the accuracy of corrections sent to the Rover. The measured accuracy and progress are shown on the screen. This process migh take a few minutes.

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3D Accuracy - Positioning accuracy estimation for the last measurement (single measurement) Mean 3D STD - Standard deviation of the accuracy after Survey-In process started

Survey-In completed

After Survey-In process is completed SmartAP GCS will start sending corrections to the Rover. Survey-In status will change from In Progress to Completed.

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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 gets corrections. D-GNSS mode becomes active after a few seconds since the base station module starts sending corrections.

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RTK Modes

RTK has two modes: Float and Fixed. Float mode is easier to reach, usually it 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, accuracy will be higher but the process might take some time.

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What will happen if the Rover looses connection with Base station?

The drone will continue flying, probably with slightly lower accuracy, however, if the connection will not be regained in 60 seconds GNSS module will go into regular mode. Once the connection is established back the system will be back in RTK mode.