First I apologize if this has been covered in the manual or on this forum extensively. I know I've seen the topic come up but I can't find anything meaningful when I search here or the manual.

If I take off from the top of a hill or mountain and fly over the edge of it, what altitude will my aircraft report? Let's say I ascend to 100ft ATO (above take off). As long as I'm flying in that immediate area, I'm also 100 ft AGL (above ground level).

If I fly over a cliff with a 200 foot drop, I'll still be 100 ft ATO but 300 ft AGL.

-What will the Mavic indicate as my altitude at that point?

-What happens if I DESCEND below the take off point, to 150 ft AGL (50 ft below take off point).

-What happens if I hit RTH? (Say RTH is set for 120 feet ATO point) and I'm still over the cliff flying at 300 ft AGL? Or below the take off point altitude?

The altitude is measured from the home point (where you take off from) and that is Zero.
If you fly off a cliff and descend below your takeoff altitude you'll get a minus altitude.
If you fly over a cliff at 100ft, it will still say 100ft.
If your RTH is set to 100ft, then no matter how far you descend (dependent of amount of battery power left) the aircraft will ascend up to ground level and then to the RTH height of 100ft.

DJI-Ken Posted at 2016-12-29 15:14
The altitude is measured from the home point (where you take off from) and that is Zero.
If you fly off a cliff and descend below your takeoff altitude you'll get a minus altitude.
If you fly over a cliff at 100ft, it will still say 100ft.

Awesome. Thanks very much for the detailed answer Ken! So, as long as I'm cognizant of the remaining battery life to ensure I can get home, there are no issues with 'negative' altitude?

zach5150 Posted at 2016-12-29 15:43
Awesome. Thanks very much for the detailed answer Ken! So, as long as I'm cognizant of the remaining battery life to ensure I can get home, there are no issues with 'negative' altitude?

That is correct, you'll be fine although you may lose signal in you descend too far unless your on the edge of the cliff with line of light to the aircraft.
Also, make sure to have proper antenna orientation for the best signal, here's a good video to watch.

Thanks for asking and answering this - I was wondering about it too.
Sarge

DJI-Ken Posted at 2016-12-29 15:55
That is correct, you'll be fine although you may lose signal in you descend too far unless your on the edge of the cliff with line of light to the aircraft.
Also, make sure to have proper antenna orientation for the best signal, here's a good video to watch.

Awesome. Thanks again!

Is there a maximum negative altitude? If I take off the top of a 3800ft mountain, can I fly it to -3800ft?

Mir Posted at 2016-12-29 18:34
Is there a maximum negative altitude? If I take off the top of a 3800ft mountain, can I fly it to -3800ft?

I don't know if there's a max, but I wouldn't want to try that feat, you may lose your aircraft.

zach5150 Posted at 2016-12-29 16:28
Awesome. Thanks again!

No problem, have fun.