dargaud writes "I live in an alpine setting and I'd like to be able to remotely view various remote valleys to check for ice formations for winter climbing. I wonder if there are cheap drones that could do that. Requirements would be: GPS guided on a preset route (no remote control necessary, and anyway there's no line of sight), at least 20km autonomy, 1 or 2 cameras on the sides to record valley walls, easy launching and autonomous landing (parachute?) at predefined point, ground detection to avoid crashes (if preset route is wrong or GPS echoes on valley walls as is often the case). Is there anything commercially available cheap enough, or any DIY that doesn't require a year of assembly?"
Thus mathematics may be defined as the subject in which we never know
what we are talking about, nor whether what we are saying is true.
-- Bertrand Russell