added ground effect reporting to land detector

[RomanBapst]

Signed-off-by: Roman [email protected]

Describe problem solved by the proposed pull request
This pull request enhances the multicopter land detector to report the possibility of the vehicle being in ground effect close to the ground. This data can be used by the estimator to trigger ground effect compensation (dead-band on baro innovations). This is useful for vehicles that are heavily affected by ground effect and reveal the "ballooning on landing" effect.

Describe possible alternatives
If the vehicle does not have any means to measure the distance to the ground then judgment whether it is close to the ground is quite hard. The in_ground_effect logic in the land detector could be further improved by taking into account specific landing profiles for the user (e.g. when close to the ground the user would reduce sink rate prior to touching down).
However, my preferred solution would be to use a range finder and rely on the terrain estimate from the estimator.

What is missing here
I commented the line which enables the ground effect compensation in the ekf.
I think we need a parameter to deactivate it by default as not all vehicles have problems with the baro near the ground.

[RomanBapst]

Next steps

• add parameter to activate ground effect triggering in the ekf?
• if valid use distance to the ground estimate in the land detector to decide when to trigger in_ground_effect

[JohannesBrand]

@RomanBapst a very practical question: does this influence any of the other flags in the land detector: landed, ground_contact or maybe_landed ?

[RomanBapst]

@JohannesBrand No it does not affect any other flag directly.

[xdwgood]

The effect of the near-surface effect on the barometer is compensated in ekf.
Landing detection is concerned with the speed in the z direction, not the other factors that affect speed.
My personal understanding of landing detection does not depend on it.

[RomanBapst]

@xdwgood I'm not sure what exactly you meant with your comment.

The effect of the near-surface effect on the barometer is compensated in ekf.

This is technically true but the compensation is never activated. The ekf offers an API to activate the ground effect compensation but it's not used anywhere.

[RomanBapst]

@dagar @MaEtUgR Anybody care for a review?

[RomanBapst]

@EliaTarasov Are you still interested in this? I know you were trying to do something similar in #10950

[EliaTarasov]

@RomanBapst yes im still interested in this pr and will have a look again. My last question was not answered so i have failed to achieve any substantional result.

[RomanBapst]

@EliaTarasov In position / altitude mode there is no way you can say for sure if the user intends to land or not. I added some logic into the land detector which basically makes sure that the vehicle is not moving horizontally and the descend speed is above a threshold. We could slightly improve the logic by requiring the descend rate to be in a certain range (if descending too fast assume that we are not near ground). You can actually trigger the condition even if you are not close to the ground. However, based on my experience you don't see a noticeable degradation of the height state.

[RomanBapst]

@EliaTarasov I think this PR together with the parameter you added to enable ground effect compensation would be a good start. We can then add more logic:

• in auto mode only compensate if in landing or takeoff mode
• apply always if vehicle is on the ground and armed
• use terrain estimate if available

[EliaTarasov]

@RomanBapst ok so i will add parameter to modules/ekf2_main.cpp and modules/ekf2_params.c to handle logic from your PR and we can proceed then.

[RomanBapst]

@EliaTarasov Sounds good!

[EliaTarasov]

@RomanBapst i've added the draft. Is it what we are looking for? Also, if there is a way to continue in your original pr and to avoid duplicating please let me know.

[RomanBapst]

@EliaTarasov See my comment in your draft

[xdwgood]

@RomanBapst I mean, landing detection shouldn't monitor too much state, and the near-ground impact is ultimately vz or a high estimate. Landing detection requires vz or vertical height.
To give an extreme example: if a future sensor receives effects from light intensity and temperature, it affects speed or position estimation. From a modular point of view, we should not monitor temperature/light intensity in landing detection. These effects should be handled in sensor drive or EKF.

----From a student 😃

[RomanBapst]

Closing in favor of #11592