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89855926ef
* sensors: move GPS antenna offsets to per-receiver parameters
Move antenna position configuration from the single EKF2_GPS_POS_X/Y/Z
parameter set into per-receiver SENS_GPS{0,1}_OFF{X,Y,Z} parameters in
the sensors module. Each offset slot is matched to a physical receiver
by device ID (SENS_GPS{0,1}_ID), falling back to uORB instance index
when no IDs are configured.
The antenna offset is now carried through the SensorGps uORB message
and blended alongside other GPS states when multi-receiver blending is
active, so EKF2 receives the correct lever arm for whichever receiver
(or weighted combination) is selected.
- Add antenna_offset_{x,y,z} fields to SensorGps.msg
- Remove EKF2_GPS_POS_X/Y/Z params; EKF2 reads offset from gnssSample
- Add SENS_GPS{0,1}_ID and SENS_GPS{0,1}_OFF{X,Y,Z} params (module.yaml)
- Blend antenna offsets in GpsBlending (weighted average)
- Add unit tests for single, blended, and failover antenna offset cases
- Migrate params.c to module.yaml for the vehicle_gps_position module
* sensors: gps_blending: add asymmetric weight and fallthrough offset tests
Add two additional antenna offset test cases:
- dualReceiverAsymmetricWeightAntennaOffset: verify that unequal eph
values produce correctly skewed blend weights (0.8/0.2) and that the
output antenna offset reflects the weighted average
- blendingFallthroughAntennaOffset: verify that when blending is enabled
but can_do_blending evaluates false (eph=0), the non-blending path
correctly assigns the selected receiver's antenna offset
* feat(param_translation): translate EKF2_GPS_POS_ to SENS_GPS0_OFF_
* fix(msgs): proper formatting
* chore(msg): 0 if invalid/unknown
* fix(ROMFS): migrate EKF2_GPS_POS_ params
* fix(docs): migrate EKF2_GPS_POS_ params
* fix(blending): unsigned param
* Update msg/SensorGps.msg
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
* fix(sensors/gps): remove 'values:' tag in module.yaml
* fix(sensors/gps): unsigned instance index
* fix(blending): restore const on gps_blend_states()
Move antenna offset blending into blend_gps_data() where the
weights are computed, keeping gps_blend_states() const.
* fix(sensors/gps): fix msg annotation and restore SENS_GPS_PRIME values
Remove incorrect @invalid NaN annotation from antenna offset fields
(0.0 default is correct, not a sentinel). Restore values tag for
SENS_GPS_PRIME so QGC shows a dropdown.
* fix(gps_blending): fix pre-existing bug to clear _gps_updated flags
The loop iterates over i but always clears gps_select_index. The intent is to clear
all updated flags, but only the selected one gets cleared (N times)
* test(gps_blending): add stale update flag regression test
34 lines
3.3 KiB
Markdown
34 lines
3.3 KiB
Markdown
# Mounting a Compass (or GNSS/Compass)
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Compass and GNSS/Compass modules should be mounted on the frame as far away from motor/ESC power lines and other sources of electromagnetic interference as possible, and [oriented](#compass-orientation) upright with the direction marker pointing towards the front of the vehicle.
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You should also configure PX4 to [set the position](#position) of the receiver relative to the centre-of-gravity (CoG).
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On multicopters it is common to mount the compass on a pedestal, while for fixed-wing and VTOL vehicles the compass is usually mounted on a wing.
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## Compass Orientation
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The compass should ideally be oriented so that it is upright and the direction marker is pointing towards the front of the vehicle (the default orientation), but if needed can be oriented at multiples of 45° from this attitude (in any axis) as defined in the [standard MAVLink orientations](https://mavlink.io/en/messages/common.html#MAV_SENSOR_ORIENTATION) (these follow the same frame convention as when [orienting the flight controller](../config/flight_controller_orientation.md#calculating-orientation)).
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The diagram below shows the heading marker on the Pixhawk 4 flight controller and compass.
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PX4 will automatically detect the orientation for any of these standard orientations during [compass calibration](../config/compass.md) ([by default](../advanced_config/parameter_reference.md#SENS_MAG_AUTOROT)).
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The compass can also be mounted at any other "custom euler angles", but in this case you will need to manually configure the orientations.
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For more information see [Setting the Compass Orientation](../config/flight_controller_orientation.md#setting-the-compass-orientation) in _Flight Controller/Sensor Orientation_.
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## Position
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In order to compensate for the relative motion between the receiver and the CoG, you should [configure](../advanced_config/parameters.md) the following parameters to set the offsets: [SENS_GPS0_OFFX](../advanced_config/parameter_reference.md#SENS_GPS0_OFFX), [SENS_GPS0_OFFY](../advanced_config/parameter_reference.md#SENS_GPS0_OFFY) and [SENS_GPS0_OFFZ](../advanced_config/parameter_reference.md#SENS_GPS0_OFFZ).
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This is important because the body frame estimated by the EKF will converge on the location of the GNSS module and assume it to be at the CoG. If the GNSS module is significantly offset from the CoG, then rotation around the COG will be interpreted as an altitude change, which in some flight modes (such as position mode) will result in unnecessary corrections.
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It is particularly important if using [RTK GNSS](../advanced/rtk_gps.md) which has centimeter-level accuracy, because if the offsets are not set then GNSS measurements will often be rejected as inconsistent with the current EFK estimate.
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::: details Explanation
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For example, if the GNSS module is 10cm above the CoG, and the IMU is located at the GoG, a pitch motion of 1 rad/s will create a GNSS velocity measurement of 10cm/s _even though the CoG isn't moving_.
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If the speed accuracy of the GNSS receiver is 1cm/s, the EKF might stop trusting the measurements because they appear inconsistent (wrong by 10x the accuracy).
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If the offsets are defined, the EKF will correct the measurements using the gyro data.
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:::
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