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59 lines
3.9 KiB
Markdown
59 lines
3.9 KiB
Markdown
# RTK GPS Heading with Dual u-blox F9P
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Two u-blox F9P [RTK GPS](../gps_compass/rtk_gps.md) modules mounted on a vehicle can be used to accurately compute a heading angle (i.e. an alternative to compass-based heading estimation).
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The two GPS devices in this scenario are referred to as the _Moving Base_ and _Rover_.
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## Supported Devices
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This feature works on F9P devices that support CAN or expose the GPS UART2 port.
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The following devices are supported:
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- [ARK RTK GPS](https://arkelectron.com/product/ark-rtk-gps/) (arkelectron.com)
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- [SparkFun GPS-RTK2 Board - ZED-F9P](https://www.sparkfun.com/sparkfun-gps-rtk2-board-zed-f9p-qwiic-gps-15136.html) (www.sparkfun.com)
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- [SIRIUS RTK GNSS ROVER (F9P)](https://store-drotek.com/911-sirius-rtk-gnss-rover-f9p.html) (store-drotek.com)
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- [mRo u-blox ZED-F9 RTK L1/L2 GPS](https://store.mrobotics.io/product-p/m10020d.htm) (store.mrobotics.io)
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- [Holybro H-RTK F9P Helical or Base](https://holybro.com/products/h-rtk-f9p-gnss-series) (Holybro Store)
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- [Holybro DroneCAN H-RTK F9P Rover or Helical](https://holybro.com/collections/dronecan-h-rtk) (Holybro Store)
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- [CUAV C-RTK 9Ps](https://store.cuav.net/shop/c-rtk-9ps/) (CUAV Store)
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::: info
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- [Freefly RTK GPS](../gps_compass/rtk_gps_freefly.md) and [Holybro H-RTK F9P Rover Lite](../gps_compass/rtk_gps_holybro_h-rtk-f9p.md) cannot be used because they do not expose the CAN or UART2 port.
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- Supported devices are also listed in [RTK GNSS (GPS) > Supported Devices](../gps_compass/rtk_gps.md#supported-devices).
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:::
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## Setup
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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](https://content.u-blox.com/sites/default/files/documents/ZED-F9P-MovingBase_AppNote_UBX-19009093.pdf), section _System Level Considerations_).
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- The application note does not state the minimal required separation between modules (50cm has been used in test vehicles running PX4).
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- The antennas can be positioned as needed, but the [GPS_YAW_OFFSET](../advanced_config/parameter_reference.md#GPS_YAW_OFFSET) must be configured:
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[RTK GPS > GPS as Yaw/Heading Source](../gps_compass/rtk_gps.md#configuring-gps-as-yaw-heading-source).
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### UART Setup
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- The UART2 of the GPS devices need to be connected together (TXD2 of the "Moving Base" to RXD2 of the "Rover")
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- 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`.
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The mapping is as follows:
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- Main GPS = Rover
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- Secondary GPS = Moving Base
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- Set [GPS_UBX_MODE](../advanced_config/parameter_reference.md#GPS_UBX_MODE) to `Heading` (1)
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- [EKF2_GPS_CTRL](../advanced_config/parameter_reference.md#EKF2_GPS_CTRL) parameter bit 3 must be set (see [RTK GPS > GPS as Yaw/Heading Source](../gps_compass/rtk_gps.md#configuring-gps-as-yaw-heading-source)).
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- [GPS_YAW_OFFSET](../advanced_config/parameter_reference.md#GPS_YAW_OFFSET) may need to be set (see [RTK GPS > GPS as Yaw/Heading Source](../gps_compass/rtk_gps.md#configuring-gps-as-yaw-heading-source)).
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- Reboot and wait until both devices have GPS reception.
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`gps status` should then show the Main GPS going into RTK mode, which means the heading angle is available.
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### CAN Setup
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Refer to the CAN RTK GPS documentation for each specific device for the setup instructions (such as [ARK RTK GPS > Setting Up Moving Baseline & GPS Heading](../dronecan/ark_rtk_gps.md#setting-up-moving-baseline-gps-heading))
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::: info
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If using RTK with a fixed base station the secondary GPS will show the RTK state w.r.t. the base station.
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:::
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## Further Information
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- [ZED-F9P Moving base applications (Application note)](https://content.u-blox.com/sites/default/files/documents/ZED-F9P-MovingBase_AppNote_UBX-19009093.pdf) - General setup/instructions.
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- [RTK GPS > GPS as Yaw/Heading Source](../gps_compass/rtk_gps.md#configuring-gps-as-yaw-heading-source)
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