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docs(navigator): [geofence] added some more warnings about limitations (#28001)

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* [docs][geofence] added some more warnings about limitations

Signed-off-by: RomanBapst <bapstroman@gmail.com>

* docs(update): Minor restructure

---------

Signed-off-by: RomanBapst <bapstroman@gmail.com>
Co-authored-by: Hamish Willee <hamishwillee@gmail.com>
This commit is contained in:
Roman Bapst
2026-07-22 08:29:02 +03:00
committed by GitHub
parent dfe32bf6c0
commit 2829c928c4
2 changed files with 18 additions and 7 deletions
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23
docs/en/flight_modes/return.md
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@@ -160,6 +160,8 @@ In this return type the vehicle:
## Geofence Awareness {#geofence_awareness}
<Badge type="tip" text="main (PX4 v1.19)" />
For most of the return types (including the default home/rally point return type) the return path is chosen to avoid breaching any geofence.
Planning is purely horizontal: the altitude profile is unaffected, and only the lateral path is adjusted to avoid the fence.
If no geofence is set, the vehicle flies a direct path to the destination.
@@ -173,14 +175,9 @@ If no such point exists, or if the autopilot fails to plan a feasible path (e.g.
The estimated time for return is based on the current shortest horizontal path to the destination and may change if the geofence is updated.
:::
::: warning
Geofence awareness currently supports a maximum of 99 polygon vertices in total (circles count as 8 vertices each).
If this limit is exceeded, the autopilot falls back to a direct path as described above.
:::
::: warning
There is no absolute guarantee that the vehicle will not breach a geofence on the return path.
Things like path tracking error, wind and other disturbances may cause temporary violation of the geofence.
Things like path tracking error, wind and other disturbances may cause temporary violation of the geofence, while some of the [geofence limitations](#geofence-limitations) below may disable geofence-aware return altogether.
It is therefore very important to consider this possibility and especially to review the geofence breach action (e.g. [GF_ACTION](../advanced_config/parameter_reference.md#GF_ACTION)).
:::
@@ -208,6 +205,20 @@ The figures below show an exclusion zone and an inclusion zone.
![Inclusion Zone](../../assets/flight_modes/rtl_geofence_inclusion.jpg)
### Geofence Limitations
- Geofence awareness currently supports a maximum of 99 polygon vertices in total (circles count as 8 vertices each).
If this limit is exceeded, the autopilot falls back to a direct path as described above.
- The autopilot does not check at upload time whether every part of the allowed area is still reachable once the [safety margin](#shortest-path-calculation) has been applied.
A region can be "cut off" by the margin — for example where several exclusion zones overlap — without any error being reported when the geofence is uploaded.
The error is only reported when a return is triggered and no feasible path can be found, at which point the vehicle falls back to flying directly to the destination.
As a result you may believe that every region is reachable when in fact some are not.
- If the autopilot falls back to a direct path (for any of the reasons described above), a configured geofence breach action ([GF_ACTION](../advanced_config/parameter_reference.md#GF_ACTION)) still applies.
For example, if the direct path breaches a geofence, the configured action (such as flight termination) will be carried out.
- The safety margin in the [Shortest-path Calculation](#shortest-path-calculation) above may not be appropriate for all vehicles.
It is derived from [NAV_LOITER_RAD](../advanced_config/parameter_reference.md#NAV_LOITER_RAD) for fixed-wing and VTOL vehicles, and from twice [NAV_ACC_RAD](../advanced_config/parameter_reference.md#NAV_ACC_RAD) for multicopters.
It is not directly configurable.
## Minimum Return Altitude
For most [return types](#return_types) a vehicle will ascend to a _minimum safe altitude_ before returning (unless already above that altitude), in order to avoid any obstacles between it and the destination.

2
docs/en/releases/main.md
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@@ -48,7 +48,7 @@ Please continue reading for [upgrade instructions](#upgrade-guide).
### Safety
- TBD
- [Geofence Aware Return mode](../flight_modes/return.md#geofence_awareness). ([PX4-Autopilot#27145: feat(navigator): Geofence Aware RTL](https://github.com/PX4/PX4-Autopilot/pull/27145), [PX4-Autopilot#28001: docs(navigator): [geofence] added some more warnings about limitations](https://github.com/PX4/PX4-Autopilot/pull/28001)).
### Estimation