# RTK GPS Heading with Dual u-blox F9P

Two u-blox F9P RTK GPS modules mounted on a vehicle can be used to accurately compute a heading angle (i.e. an alternative to compass-based heading estimation). The two GPS devices in this scenario are referred to as the Moving Base and Rover.

# Supported Devices

This feature works on F9P devices that expose the GPS UART2 port (access to the port is required for setup).



# Setup

Ideally the two antennas should be identical, on the same level/horizontal plane and oriented the same way, and on an identical ground plane size and shape (Application note (opens new window), section System Level Considerations).

In overview:

  • The UART2 of the GPS devices need to be connected together (TXD2 of the "Moving Base" to RXD2 of the "Rover")
  • Connect UART1 on each of the GPS to (separate) unused UART's on the autopilot, and configure both of them as GPS with baudrate set to Auto. The mapping is as follows:
    • Main GPS = Rover
    • Secondary GPS = Moving Base
  • Set GPS_UBX_MODE to Heading (1)
  • EKF2_AID_MASK parameter bit 7 must be set (see GPS > Configuration > GPS as Yaw/Heading Source).
  • GPS_YAW_OFFSET may need to be set (see GPS > Configuration > GPS as Yaw/Heading Source).
  • Reboot and wait until both devices have GPS reception. gps status should then show the Main GPS going into RTK mode, which means the heading angle is available.


If using RTK with a fixed base station the secondary GPS will show the RTK state w.r.t. the base station.

# Further Informaiton