I had quite a hard time configuring APM::Plane to only have an altitude deck so that if I fly too low, AP takes over and goes back to a safe altitude.
I think I also hit at least one small bug in the code in the process (you cannot set a minimum altitude without setting a maximum altitude too).
Either way, I documented it all here:
http://marc.merlins.org/perso/rc/post_2015-11-06_Using-Ardupilot-Geofencing-As-An-Altitude-Deck.html
Comments
Eh Tom. I'm sure auto land works past the geofence, but I don't use it, mostly because I don't fly from fields where I'd feel comfortable doing an auto land.
So I always take off manually, turn on geofence, fly, fly back, turn off geofence, and land manually.
Also, I'm a long time RC pilot, so I like to fly manually anyway, I kind of think of ardupilot as traction/stability control on my car, and only take over or help if I'm screwing up :)
There was a fix at one point to ignore fences (and RTL changes) during landing. Have you tried an auto-land while still fenced?
Barry, good question. I have a failsafe/normal flight/slow flight switch. In normal flight it sends the right signal to make the altitude fence work. For landing, I flip back to slow flight and that removes the geofence, allowing me to fly below the altitude deck, and land.
Otherwise, as you guessed, it would have been impossible to land without running out of motor batteries.
Interesting work around. How do you achieve a controlled landing? Do you have a defeat switch option on that mode?