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236 lines
18 KiB
Markdown
236 lines
18 KiB
Markdown
# RTK GNSS (GPS)
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[Real Time Kinematic (RTK)](https://en.wikipedia.org/wiki/Real_Time_Kinematic) GNSS/GPS systems provide centimeter-level accuracy, allowing PX4 to be used in applications like precision surveying (where pinpoint accuracy is essential).
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This feature requires _QGroundControl_ running on a laptop/PC and a vehicle with a WiFi or Telemetry radio link to the ground station laptop.
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::: info
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Some RTK GNSS setups can provide yaw/heading information, as an alternative to the compass:
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- [RTK GPS Heading with Dual u-blox F9P](../gps_compass/u-blox_f9p_heading.md).
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- GPS directly output yaw (see table below).
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:::
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## Supported Devices
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PX4 supports the [u-blox M8P](https://www.u-blox.com/en/product/neo-m8p), [u-blox F9P](https://www.u-blox.com/en/product/zed-f9p-module) and the [Trimble MB-Two](https://oemgnss.trimble.com/en/products/receiver-modules/mb-two) GPS, and products that incorporate them.
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The RTK compatible devices below that are expected to work with PX4 (it omits discontined devices).
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The table indicates devices that also output yaw, and that can provide yaw when two on-vehicle units are used.
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It also highlights devices that connect via the CAN bus, and those which support PPK (Post-Processing Kinematic).
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| Device | GPS | Compass | [DroneCAN] | [GPS Yaw] | PPK |
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| :-------------------------------------------------------------------------------------------------------- | :------------------: | :------: | :--------: | :---------------------------------: | :-: |
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| [ARK G5 RTK GPS](../dronecan/ark_g5_rtk_gps.md) | [mosaic-G5 P3] | IIS2MDC | ✓ | | |
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| [ARK G5 RTK HEADING GPS](../dronecan/ark_g5_rtk_heading_gps.md) | [mosaic-G5 P3H] | IIS2MDC | ✓ | [Heading Capability][mosaic-G5 P3H] | |
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| [ARK RTK GPS](../dronecan/ark_rtk_gps.md) | F9P | BMM150 | ✓ | [Dual F9P] | |
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| [ARK RTK GPS L1 L5](../dronecan/ark_rtk_gps_l1_l2.md) | F9P | BMM150 | ✓ | | |
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| [ARK MOSAIC-X5 RTK GPS](../dronecan/ark_mosaic__rtk_gps.md) | Mosaic-X5 | IIS2MDC | ✓ | [Septentrio Dual Antenna] | |
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| [ARK X20 RTK GPS](../dronecan/ark_x20_rtk_gps.md) | X20P | IIS2MDC | ✓ | | |
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| [CUAV C-RTK GPS](../gps_compass/rtk_gps_cuav_c-rtk.md) | M8P/M8N | ✓ | | | |
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| [CUAV C-RTK2](../gps_compass/rtk_gps_cuav_c-rtk2.md) | F9P | ✓ | | [Dual F9P] | |
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| [CUAV C-RTK 9Ps GPS](../gps_compass/rtk_gps_cuav_c-rtk-9ps.md) | F9P | RM3100 | | [Dual F9P] | |
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| [CUAV C-RTK2 PPK/RTK GNSS](../gps_compass/rtk_gps_cuav_c-rtk.md) | F9P | RM3100 | | | ✓ |
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| [CubePilot Here+ RTK GPS](../gps_compass/rtk_gps_hex_hereplus.md) | M8P | HMC5983 | | | |
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| [CubePilot Here3 CAN GNSS GPS (M8N)](https://www.cubepilot.org/#/here/here3) | M8P | ICM20948 | ✓ | | |
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| [Drotek SIRIUS RTK GNSS ROVER (F9P)](https://store-drotek.com/911-sirius-rtk-gnss-rover-f9p.html) | F9P | RM3100 | | [Dual F9P] | |
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| [DATAGNSS NANO HRTK Receiver](../gps_compass/rtk_gps_datagnss_nano_hrtk.md) | [D10P] | IST8310 | | ✘ | |
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| [DATAGNSS GEM1305 RTK Receiver](../gps_compass/rtk_gps_gem1305.md) | TAU951M | IST8310 | | ✘ | |
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| [Femtones MINI2 Receiver](../gps_compass/rtk_gps_fem_mini2.md) | FB672, FB6A0 | ✓ | | | |
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| [Freefly RTK GPS](../gps_compass/rtk_gps_freefly.md) | F9P | IST8310 | | | |
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| [Holybro H-RTK ZED-F9P RTK Rover (DroneCAN variant)](../dronecan/holybro_h_rtk_zed_f9p_gps.md) | F9P | RM3100 | ✓ | [Dual F9P] | |
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| [Holybro H-RTK ZED-F9P RTK Rover](https://holybro.com/collections/h-rtk-gps/products/h-rtk-zed-f9p-rover) | F9P | RM3100 | | [Dual F9P] | |
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| [Holybro H-RTK F9P Ultralight](https://holybro.com/products/h-rtk-f9p-ultralight) | F9P | IST8310 | | [Dual F9P] | |
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| [Holybro H-RTK F9P Helical or Base](../gps_compass/rtk_gps_holybro_h-rtk-f9p.md) | F9P | IST8310 | | [Dual F9P] | |
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| [Holybro DroneCAN H-RTK F9P Helical](https://holybro.com/products/dronecan-h-rtk-f9p-helical) | F9P | BMM150 | ✓ | [Dual F9P] | |
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| [Holybro H-RTK F9P Rover Lite](../gps_compass/rtk_gps_holybro_h-rtk-f9p.md) | F9P | IST8310 | | | |
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| [Holybro DroneCAN H-RTK F9P Rover](https://holybro.com/products/dronecan-h-rtk-f9p-rover) | F9P | BMM150 | | [Dual F9P] | |
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| [Holybro H-RTK M8P GNSS](../gps_compass/rtk_gps_holybro_h-rtk-m8p.md) | M8P | IST8310 | | | |
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| [Holybro H-RTK Unicore UM982 GPS](../gps_compass/rtk_gps_holybro_unicore_um982.md) | UM982 | IST8310 | | [Unicore Dual Antenna] | |
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| [LOCOSYS Hawk R1](../gps_compass/rtk_gps_locosys_r1.md) | MC-1612-V2b | | | | |
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| [LOCOSYS Hawk R2](../gps_compass/rtk_gps_locosys_r2.md) | MC-1612-V2b | IST8310 | | | |
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| [mRo u-blox ZED-F9 RTK L1/L2 GPS](https://store.mrobotics.io/product-p/m10020d.htm) | F9P | ✓ | | [Dual F9P] | |
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| [Navisys L1/L2 ZED-F9P RTK - Base only](https://www.navisys.com.tw/productdetail?name=GR901&class=RTK) | F9P | | | | |
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| [RaccoonLab L1/L2 ZED-F9P][RaccoonLab L1/L2 ZED-F9P] | F9P | RM3100 | ✓ | | |
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| [RaccoonLab L1/L2 ZED-F9P with external antenna][RaccnLabL1L2ZED-F9P ext_ant] | F9P | RM3100 | ✓ | | |
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| [Septentrio AsteRx-m3 Pro](../gps_compass/septentrio_asterx-rib.md) | AsteRx | ✓ | | [Septentrio Dual Antenna] | ✓ |
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| [Septentrio mosaic-go](../gps_compass/septentrio_mosaic-go.md) | mosaic X5 / mosaic H | ✓ | | [Septentrio Dual Antenna] | ✓ |
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| [SIRIUS RTK GNSS ROVER (F9P)](https://store-drotek.com/911-sirius-rtk-gnss-rover-f9p.html) | F9P | ✓ | | [Dual F9P] | |
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| [SparkFun GPS-RTK2 Board - ZED-F9P](https://www.sparkfun.com/products/15136) | F9P | ✓ | | [Dual F9P] | |
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| [Trimble MB-Two](../gps_compass/rtk_gps_trimble_mb_two.md) | F9P | ✓ | | ✓ | |
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<!-- links used in above table -->
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[RaccnLabL1L2ZED-F9P ext_ant]: https://docs.raccoonlab.co/guide/gps_mag_baro/gnss_external_antenna_f9p_v320.html
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[RaccoonLab L1/L2 ZED-F9P]: https://docs.raccoonlab.co/guide/gps_mag_baro/gps_l1_l2_zed_f9p.html
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[Dual F9P]: ../gps_compass/u-blox_f9p_heading.md
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[Septentrio Dual Antenna]: ../gps_compass/septentrio.md#gnss-based-heading
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[Unicore Dual Antenna]: ../gps_compass/rtk_gps_holybro_unicore_um982.md#enable-gps-heading-yaw
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[DATAGNSS GEM1305 RTK]: ../gps_compass/rtk_gps_gem1305.md
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[DroneCAN]: ../dronecan/index.md
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[GPS Yaw]: #configuring-gps-as-yaw-heading-source
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[mosaic-G5 P3]: https://www.septentrio.com/en/products/gnss-receivers/gnss-receiver-modules/mosaic-G5-P3
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[mosaic-G5 P3H]: https://www.septentrio.com/en/products/gnss-receivers/gnss-receiver-modules/mosaic-G5-P3H
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[D10P]: https://docs.datagnss.com/gnss/gnss_module/D10P_RTK
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Notes:
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- ✓ or a specific part number indicate that a features is supported, while ✘ or empty show that the feature is not supported.
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"?" indicates "unknown".
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- Where possible and relevant the part name is used (i.e. ✓ in the GPS column indicates that a GPS module is present but the part is not known).
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- Some RTK modules can only be used in a particular role (base or rover), while others can be used interchangeably.
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- The list may omit some discontinued hardware that is still supported.
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For example [CubePilot Here+ RTK GPS](../gps_compass/rtk_gps_hex_hereplus.md) is discontinued and may be removed from the list in a future release.
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Check earlier versions if a discontinued module is not mentioned here.
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## Positioning Setup/Configuration
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RTK positioning requires a _pair_ of [RTK GNSS devices](#supported-devices): a "base" for the ground station and a "rover" for the vehicle.
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In addition you will need:
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- A _laptop/PC_ with QGroundControl (QGroundControl for Android/iOS do not support RTK)
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- A vehicle with a WiFi or Telemetry radio link to the laptop.
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::: info
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_QGroundControl_ with a base module can theoretically enable RTK GPS for multiple vehicles/rover modules.
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At time of writing this use case has not been tested.
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:::
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### Hardware Setup
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#### Rover RTK Module (Vehicle)
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The connection method and cables/connectors required depends on the selected RTK module (and on the [flight controller](../flight_controller/index.md)).
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Most are connected via the flight controller's GPS port, in the same way as any other GPS module.
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Some are connected to the [CAN](../can/index.md) bus (i.e. using [DroneCAN](../dronecan/index.md)).
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See [documentation for the selected device](#supported-devices), general [GNSS Hardware/Configuration Setup](../gps_compass/index.md#hardware-setup), and [DroneCAN](../dronecan/index.md) for more information on wiring and configuration.
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#### Base RTK Module (Ground)
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Connect the base module to _QGroundControl_ via USB.
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The base module must not be moved while it is being used.
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:::tip
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Choose a position where the base module won't need to be moved, has a clear view of the sky, and is well separated from any buildings.
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Often it is helpful to elevate the base GPS, by using a tripod or mounting it on a roof.
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:::
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#### Telemetry Radio/WiFi
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The vehicle and ground control laptop must be connected via [wifi or a radio telemetry link](../telemetry/index.md).
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The link _must_ use the MAVLink 2 protocol as it makes more efficient use of the channel.
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This should be set by default, but if not, follow the [MAVLink2 configuration instructions](#mavlink2) below.
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### RTK Connection Process
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The RTK GPS connection is essentially plug and play:
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1. Start _QGroundControl_ and attach the base RTK GPS via USB to the ground station.
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The device is recognized automatically.
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1. Start the vehicle and make sure it is connected to _QGroundControl_.
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:::tip
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_QGroundControl_ displays an RTK GPS status icon in the top icon bar while an RTK GPS device is connected (in addition to the normal GPS status icon).
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The icon is red while RTK is being set up, and then changes to white once RTK GPS is active.
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You can click the icon to see the current state and RTK accuracy.
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:::
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1. _QGroundControl_ then starts the RTK setup process (known as "Survey-In").
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Survey-In is a startup procedure to get an accurate position estimate of the base station.
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The process typically takes several minutes (it ends after reaching the minimum time and accuracy specified in the [RTK settings](#rtk-gps-settings)).
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You can track the progress by clicking the RTK GPS status icon.
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1. Once Survey-in completes:
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- The RTK GPS icon changes to white and _QGroundControl_ starts to stream position data to the vehicle:
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- Vehicle GPS switches to RTK mode.
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The new mode is displayed in the _normal_ GPS status icon (`3D RTK GPS Lock`):
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### Configuring GPS as Yaw/Heading Source
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GPS can be used as a source for yaw fusion when using a single device with two antenna where _yaw output is supported by the device_, or when using some [RTK GPS Setups with Dual u-blox F9P](../gps_compass/u-blox_f9p_heading.md).
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Using GPS as a heading source has the benefit that yaw calculations are not impacted by magnetic interference.
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Both approaches work comparing the time taken for a GNSS signal to reach two separated antennas.
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The minimum distance between antenna depends on the device but is of the order of 50 cm (check manufacturer documentation).
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The devices that can be used are listed in this way are listed in the **GPS Yaw** column of the table above, such as [Septentrio AsteRx-m3 Pro](../gps_compass/septentrio_asterx-rib.md), [Holybro H-RTK Unicore UM982 GPS](../gps_compass/rtk_gps_holybro_unicore_um982.md), and [Trimble MB-Two](../gps_compass/rtk_gps_trimble_mb_two.md).
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The links in the table take you to the device-specific PX4 configuration.
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Generally when using a GNSS as a source of yaw information you will need to configure the following parameters:
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| Parameter | Setting |
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| -------------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------- |
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| [GPS_YAW_OFFSET][GPS_YAW_OFFSET] | The angle made by the _baseline_ (the line between the two GPS antennas) relative to the vehicle x-axis (front/back axis, as shown [here][fc_orientation]). |
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| [EKF2_GPS_CTRL][EKF2_GPS_CTRL] | Set bit position 3 "Dual antenna heading" to `1` (i.e. add 8 to the parameter value). |
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<!-- links used in table above -->
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[GPS_YAW_OFFSET]: ../advanced_config/parameter_reference.md#GPS_YAW_OFFSET
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[EKF2_GPS_CTRL]: ../advanced_config/parameter_reference.md#EKF2_GPS_CTRL
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[fc_orientation]: ../config/flight_controller_orientation.md#calculating-orientation
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:::tip
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If using this feature, all other configuration should be setup up as normal (e.g. [RTK Positioning](../gps_compass/rtk_gps.md#positioning-setup-configuration)).
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:::
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### Optional PX4 Configuration
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The following settings may need to be changed (using _QGroundControl_).
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#### RTK GPS settings
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The RTK GPS settings are specified in the _QGroundControl_ [General Settings](https://docs.qgroundcontrol.com/master/en/qgc-user-guide/settings_view/general.html#rtk_gps) (**SettingsView > General Settings > RTK GPS**).
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These settings define the minimum duration and minimum accuracy for completing the RTK GPS setup process (known as "Survey-In).
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:::tip
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You can save and reuse a base position in order to save time: perform Survey-In once, select _Use Specified Base Position_ and press **Save Current Base Position** to copy in the values for the last survey.
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The values will then persist across QGC reboots until they are changed.
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:::
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#### MAVLink2
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The MAVLink2 protocol must be used because it makes more efficient use of lower-bandwidth channels.
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This should be enabled by default on recent builds.
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To ensure MAVLink2 is used:
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- Update the telemetry module firmware to the latest version (see [QGroundControl > Setup > Firmware](https://docs.qgroundcontrol.com/master/en/qgc-user-guide/setup_view/firmware.html)).
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- Ensure [MAV_PROTO_VER](../advanced_config/parameter_reference.md#MAV_PROTO_VER) is set to 2 (see [QGroundControl Setup > Parameters](https://docs.qgroundcontrol.com/master/en/qgc-user-guide/setup_view/parameters.html))
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#### Tuning
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You may also need to tune some parameters as the default parameters are tuned assuming a GPS accuracy in the order of meters, not centimeters.
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For example, you can decrease [EKF2_GPS_V_NOISE](../advanced_config/parameter_reference.md#EKF2_GPS_V_NOISE) and [EKF2_GPS_P_NOISE](../advanced_config/parameter_reference.md#EKF2_GPS_P_NOISE) to 0.2.
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#### Dual Receivers
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A second GPS receiver can be used as a backup (either RTK or non RTK).
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See the [Using PX4's Navigation Filter (EKF2) > GPS](../advanced_config/tuning_the_ecl_ekf.md#gps) section.
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<!--
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- Video demonstration would be nice.
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- something that shows positioning of base, connection of RTK rover, survey in process. Some sort of short precision survey.
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-->
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## Further Information
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- [RTK-GPS (PX4-Integration)](../advanced/rtk_gps.md): Developer information about integrating RTK-GPS support into PX4.
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- [Real Time Kinematic](https://en.wikipedia.org/wiki/Real_Time_Kinematic) (Wikipedia)
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