Actual height dropping - mission waypoints at 40, drone at 33....31

In waypoint mode, I just have a bunch of waypoints at 40 above ground (with internet ground data) and for some reason my drone did start, waypoint 1, at 40, but slowly but surely the drone was dropping, I hit pause at 30m.

Why did the drone (or litchi) do this? The drone certainly knew it was dropping, and I could confirm visually it was getting lower too.

I think I worked it out, the actual slope of the terrain is more than I expected.

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At least it is good to hear the the “Above Ground” option works as intended.

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Litchi’s altitude audio callouts are referenced to the home point, and NOT to each individual waypoint. This means that if the home point is at an altitude above that of subsequent waypoints, those periodic audio callouts will indicate lower height values than the actual height of the drone above the waypoint it is currently overflying.

For some reason, I’d used Litchi for years before realizing that the audio callouts always refer to the height of the drone above the altitude of the home point, and NOT the actual height above the current overflow waypoint.

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The funny part is that I did know all this, but somehow because the video stream really also looked like the height above ground was dropping (an optical illusion I now think) I sought confirmation and got worried. But indeed my starting point is somewhat on a hill so it absolutely made sense.

Basically also, as a rule of thumb in my area very few trees are above 30m so when the drone was dropping from 40 (absolute height, but also as people here said, the 0 point) and then started quickly dropping to 35…30… 29… I panicked a bit. Also didn’t want to bother people, a drone 40m above you in a city (cars etc…) is hard to notice if you’re not looking out for it. But 30m and below it becomes obvious something is buzzing angrily above you.

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The first time I paid attention to those gradually decreasing altitude callouts I panicked and hit RTH to get my renegade drone back home before it hit a tree or building. It was only later that I realized what had been happening.

Not sure what drone you are using, but some of them use an internal calculation depending on the barometer on take off to maintain its height. If the air pressure dropped while you were flying, the drone could be out of place. I probably didn’t explain it well, since I learned it from the internet! Some guy smarter than me posted it in youtube here: Are you flying waypoint missions with your DJI Mini 2 or any other drone? Then BEWARE of THIS… - YouTube

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