Add safehomes

[tonyyng]

After a couple of recent radio failures resulted in my airplane landing itself, I came up with a way to designate a safe landing spot, instead of the location where you arm your plane.

During landing for fixed wing, the airplane circles around "home", an area which likely includes you, other pilots, parked cars, trees, etc.

This approach lets you identify alternate locations which are safe. During arming, if any of these locations are within 200m, it is used as home, instead of the point where you armed your plane.

For more details, see Safehomes.md.

[giacomo892]

Very interesting indeed! Thanks for the contribution
I'd add an option to force the plane to land at the resonably nearest safehome from the arming point during a failsafe, regardless the "200m" constraint.
You can possibly have a nice place that can handle a complete failsafe landing and it couldn't be close enough to trigger the 200m check.

[digitalentity]

Nice indeed! As @giacomo892 mentioned, this still could be improved, but we can definitely target this feature for 2.6

[stronnag]

and maybe remove set nav_rth_home_offset_* to avoid confusion.

[tonyyng]

Very interesting indeed! Thanks for the contribution
I'd add an option to force the plane to land at the resonably nearest safehome from the arming point during a failsafe, regardless the "200m" constraint.
You can possibly have a nice place that can handle a complete failsafe landing and it couldn't be close enough to trigger the 200m check.

After considering your suggestion, my preference would be to keep the implementation simple. I don't have enough knowledge or experience with this software to implement something much more complex.

The current logic is executed once when the plane is armed, designating the location that will replace home. The pilot is explicitly informed of the change in the home location. Your suggestion would involve changes at the point in time where a failsafe occurs and then executing logic to determine where to land. This is more risk than I feel comfortable writing code and testing.

In my mind, the 200m value is what I would choose for "reasonably nearest". What would you suggest as the reasonable limit for redirecting the aircraft to land elsewhere? I could increase it or change the 200m constraint to be a setting, allowing it to be set based on individual preference. I don't see this as a setting that many people are going to "tweak and tune". I just wanted an alternative to landing around the arming point.

[tonyyng]

and maybe remove set nav_rth_home_offset_* to avoid confusion.

I agree with this. These changes allow you to have the same functionality in a more reliable way.

Beyond removing the logic and setting definition, what else is involved? Release notes? Who decides if this should be done?

[stronnag]

and maybe remove set nav_rth_home_offset_* to avoid confusion.

I agree with this. These changes allow you to have the same functionality in a more reliable way.

Then please do it in the next iteration of your PR.

Beyond removing the logic and setting definition, what else is involved? Release notes? Who decides if this should be done?

It will be part of the review, the author of the original feature requested / supports its removal.

I've marked this as for the Release Note so we won't forget. Once it's merged it can be added to the draft RN.

[tonyyng]

This is more risk than I feel comfortable writing code and testing.

Having said that, if anyone else feels up to making improvements, feel free to do so.

[stronnag]

Tested with multiple safehomes. Home is selected correctly in all cases.

Flight tested for RTH, WP and F/S cases (see also #5997). Home correctly instantiated (including case when all options out of range).

[StuweFPV]

I love this idea of that new feature. however I don't agree with the 200m limit that is introduced.
On my permanent spot i have my offset distance at 300m and it works perfectly. 200m will only slightly improve the situation vs launch position as RTH but still crash the plane into the trees. By forcing me onto a 200m limit you're completely eliminating the whole offset landing idea for me to be used (and maybe others also).
Please use 200m as default but give us the option to change that limit at our own risk. I don't see why it cannot go up to at least 500m+
cheers