diff --git a/docs/en/config/safety.md b/docs/en/config/safety.md index f8a224f945..002d09641b 100644 --- a/docs/en/config/safety.md +++ b/docs/en/config/safety.md @@ -181,17 +181,22 @@ The following settings also apply, but are not displayed in the QGC UI. | Preemptive geofence triggering | [GF_PREDICT](../advanced_config/parameter_reference.md#GF_PREDICT) | (Experimental) Trigger geofence if current motion of the vehicle is predicted to trigger the breach (rather than late triggering after the breach). | | Circuit breaker for flight termination | [CBRK_FLIGHTTERM](../advanced_config/parameter_reference.md#CBRK_FLIGHTTERM) | Enables/Disables flight termination action (disabled by default). | -## Position (GNSS) Loss Failsafe +## Position Estimation Failsafes + +This section describes failsafes related to the quality of the vehicle's position estimate. + +### Position Loss Failsafe The _Position Loss Failsafe_ is triggered if the quality of the PX4 position estimate falls below acceptable levels (this might be caused by GPS loss) while in a mode that requires an acceptable position estimate. -The sections below cover first the trigger and then the failsafe action taken by the controller. ### Position Loss Failsafe Trigger -There are basically two mechanisms in PX4 to trigger position failsafes: +The position loss failsafe triggers if the position estimate becomes _invalid_. There are two mechanisms in PX4 to invalidate the position estimate: -- A timeout since the last sensor data was fused that provides direct speed or horizontal position measurements. Sensors that fall into that category are: GNSS, optical flow, airspeed, VIO, auxiliary global position. -- The estimated horizontal position accuracy exceeds a certain threshold. This check is only done on hovering systems (rotary wing vehicles or VTOLs in hover phase). +- A timeout since the last sensor data was fused that provides direct speed or horizontal position measurements. + - Sensors that fall into that category are: GNSS, optical flow, airspeed, VIO, auxiliary global position. +- The estimated horizontal position inaccuracy exceeds the threshold [COM_POS_LOW_EPH](../advanced_config/parameter_reference.md#COM_POS_LOW_EPH) + - This check is only done on hovering systems (rotary-wing vehicles or VTOLs in hover phase). For fixed-wing vehicles, refer to the [Position Accuracy Low](#position-accuracy-low-failsafe) section. The relevant parameters shown below. @@ -207,14 +212,24 @@ Multicopters will switch to [Altitude mode](../flight_modes_mc/altitude.md) if a Fixed-wing planes, and VTOLs not configured to land in hover ([NAV_FORCE_VT](../advanced_config/parameter_reference.md#NAV_FORCE_VT)), have a parameter ([FW_GPSF_LT](../advanced_config/parameter_reference.md#FW_GPSF_LT)) that defines how long they will loiter (circle with a constant roll angle ([FW_GPSF_R](../advanced_config/parameter_reference.md#FW_GPSF_R)) at the current altitude) after losing position before attempting to land. If VTOLs have are configured to switch to hover for landing ([NAV_FORCE_VT](../advanced_config/parameter_reference.md#NAV_FORCE_VT)) then they will first transition and then descend. -The relevant parameters for all vehicles shown below. +The relevant parameters are: -Parameters that only affect Fixed-wing vehicles: +| Parameter | Description | +| ----------------------------------------------------------------------------------------------- | --------------------------------------------------------------------------------------------------------------------------------------------- | +| [FW_GPSF_LT](../advanced_config/parameter_reference.md#FW_GPSF_LT) | Fixed-wing only: Loiter time (waiting at current altitude for position estimation recovery before starting to descend). Set to 0 to disable. | +| [FW_GPSF_R](../advanced_config/parameter_reference.md#FW_GPSF_R) | Fixed roll/bank angle while circling. | +| [NAV_FORCE_VT](../advanced_config/parameter_reference.md#NAV_FORCE_VT) | If true, force VTOL takeoff and landing, even in `Descend` failsafe. | -| Parameter | Description | -| ----------------------------------------------------------------------------------------- | ----------------------------------------------------------------------------------------------------------- | -| [FW_GPSF_LT](../advanced_config/parameter_reference.md#FW_GPSF_LT) | Loiter time (waiting for GPS recovery before it goes into land or flight termination). Set to 0 to disable. | -| [FW_GPSF_R](../advanced_config/parameter_reference.md#FW_GPSF_R) | Fixed roll/bank angle while circling. | +### Position Accuracy Low Failsafe + +In Fixed-wing, the position estimate is never strictly invalidated as long as we have a horizontal aiding source, such as an airspeed sensor. In that case, a separate failsafe can be configured that triggers if the position estimate inacuraccy exceeds the threshold [COM_POS_LOW_EPH](../advanced_config/parameter_reference.md#COM_POS_LOW_EPH). The failsafe action is taken if the vehicle is in mission or hold mode, otherwise it is only a warning. The relevant parameters are: + +| Parameter | Description | +| -------------------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------| +| [COM_POS_LOW_EPH](../advanced_config/parameter_reference.md#COM_POS_LOW_EPH) | Position inaccuracy threshold above which COM_POS_LOW_ACT is taken. | +| [COM_POS_LOW_ACT](../advanced_config/parameter_reference.md#COM_POS_LOW_ACT) | Failsafe action taken when position inaccuracy is above configured threshold. | + +Note that if there is no horizontal aiding source anymore, the position estimate is invalidated after `EKF2_NOAID_TOUT`, and the standard position loss failsafe applies. ## Offboard Loss Failsafe