PX4 supports global navigation satellite systems (GNSS) (including GPS, GLONASS, Galileo, BeiDou, QZSS and SBAS) using receivers that communicate via the u-blox, MTK Ashtech or Emlid protocols, or via UAVCAN. 它还支持 实时动态（RTK）GPS接收器 ，它将 GPS 系统扩展到厘米级精度。
PX4 can be used with the following compass parts (magnetometers): Bosch BMM 150 MEMS (via I2C bus), HMC5883 / HMC5983 (I2C or SPI), IST8310 (I2C) and LIS3MDL (I2C or SPI). Up to 4 internal or external magnetometers can be connected, though only one will actually be used as a heading source. The system automatically chooses the best available compass based on their internal priority (external magnetometers have a higher priority). If the primary compass fails in-flight, it will failover to the next one. If it fails before flight, arming will be denied.
:::tip When using Pixhawk-series flight controllers, we recommend using a combined GPS + Compass mounted as far away from the motor/ESC power supply lines as possible - typically on a pedestal or wing (for fixed-wing). The internal compass may be useful on larger vehicles (e.g. VTOL) where it is possible to reduce electromagnetic interference by mounting the Pixhawk a long way from power supply lines. On small vehicles an external compass is almost always required. :::
:::note
- ✓ or a specific part number indicate that a features is supported, while ✗ or empty show that the feature is not supported. "?" indicates "unknown".
- 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).
- Avionics Anonymous UAVCAN Magnetometer is a compass (not a GPS).
- Some RTK modules can only be used in a particular role (base or rover), while others can be used interchangeably. :::
Instructions for connecting the GPS (and compass, if present) are usually provided by the manufacturer (at least for more common Autopilot Hardware).
Pixhawk Series controllers typicaly have a clearly labeled port for connecting the GPS, and the compass is connected to either the I2C or SPI port/bus (depending on the device).
The Zubax GNSS 2 and Avionics Anonymous GNSS/Mag can also be connected via UAVCAN.
:::warning Pay attention to pinout when connecting the GPS module. While these are all software-compatible, there are several different pin orderings. :::
The "standard" GPS/compass configuration is provided below. Additional device-specific configuration may be provided in PX4 or manufacturer device documentation (e.g. Trimble MB-Two > Configuration).
GPS configuration on Pixhawk is handled transparently for the user - simply connect the GPS module to the port labeled GPS and everything should work.
:::note The default Serial Port Configuration works for most devices. If you are using the Trimble MB-Two you will need to modify the configuration to explicitly set the rate to 115200 baud. :::
To use a secondary GPS, attach it to any free port, and then perform a Serial Port Configuration to assign GPS_2_CONFIG to the selected port.
The following steps show how to configure a secondary GPS on the TELEM 2 port in QGroundControl:
- Find and set the parameter GPS_2_CONFIG to TELEM 2.
- Open QGroundControl and navigate to the Vehicle Setup > Parameters section.
- 选择 GPS 选项卡(1)，然后打开 GPS_2_CONFIG 参数(2)，并从下拉列表(3) 中选择 TELEM 2。
- Reboot the vehicle in order to make the other parameters visible.
- 选择 串口 选项卡，并打开 SER_TEL2_BAUD 参数 (
TELEM 2端口波特率)：将其设置为 Auto。
After setting up the second GPS port:
- Configure the ECL/EKF2 estimator to blend data from both GPS systems. For detailed instructions see: Using the ECL EKF > Dual Receivers.
GPS can be used as a source for yaw fusion when using modules where yaw output is supported by the device (e.g. Trimble MB-Two) or when using some RTK GPS Setups with Dual u-blox F9P.
When using GPS for yaw fusion you will need to configure the following parameters:
| Parameter | Setting |
|---|---|
| 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). |
| EKF2_AID_MASK | Set bit position 7 "GPS yaw fusion" to 1 (i.e. add 128 to the parameter value). |
:::tip
- If using this feature, all other configuration should be setup up as normal (e.g. RTK Positioning). :::
Compass calibration is covered in: Compass Configuration. The process is straightforward and will calibrate all connected magnetometers.
Additional configuration can be performed using the CALMAGx parameters (where x=0-3). Generally you will not need to modify these as compasses are autodetected, prioritised and are all calibrated at the same time (a possible exception is CAL_MAGx_EN which might be used to disable an internal compass). You may however wish to read them, as they will let you know which magnetometers are internal or external (CAL_MAGx_EN) and which is being uses as the main heading source (CAL_MAG_PRIME).
- GPS/RTK-GPS
- Compass
- Driver source code (Compasses)