RTL: cone: never climb more than to RTL_RETURN_ALT

[sfuhrer]

This is to prevent that a large NAV_ACC_RAD leads to very high return altitudes.

At some point we should reconsider the cone logic, seems unnecessary complicated.

Changelog Entry

For release notes:

Bugfix: RTL: cone: never climb more than to RTL_RETURN_ALT

[bresch]

Yes, we should maybe review the logic

[ryanjAA]

As a frequent RTL user, Im a big fan of this and the @bresch comment that it's overly complicated.

[hamishwillee]

As a frequent RTL user, Im a big fan of this and the @bresch comment that it's overly complicated.

@ryanjAA Just consider yourself lucky that you didn't have to document it :-( https://docs.px4.io/main/en/flight_modes/return.html#minimum-return-altitude

[ryanjAA]

@hamishwillee haha so true. You probably understand it better than anyone at this point. I always look at that page and just sigh everytime I have to think about changing the default or need to test it. Writing it would have been way more brutal… 😬

[hamishwillee]

The simple version of the theory is that if there is a more-or-less clear area around your landing target and your return is triggered within this area, then there is no need to ascent to the default return height in order to get safely to the landing point. The cone defines the safe height over the areas around the landing point. If you are above the cone you're safe, so you just fly back at your current height. If you're below the cone you're too low, so you ascend to the intersection with the cone and then return.

It kind of makes sense but I doubt anyone uses it because they wouldn't think about it.
I would use it if there was a 3d visualization tool for setting it that you could apply at the field and see the obstacles.

I recall a discussion with RomanB about an alternative, defining segments around a VTOL landing point that are know to offer a clear path. Again, that is more likely to be used because AMC has a visualisation tool for it.