[size=14.666666984558105px]Experimenting with making path in Google earth Pro and loading in Litchi, here is what I have done:

[size=14.666666984558105px]Going up
[size=14.666666984558105px]Starting point alt 53m , start flying at 30m(Waypoint 1). Litchi shows waypoint 1 Alt 30m
[size=14.666666984558105px]Finish point alt 68 m Litchi shows finish waypoint alt 46 m
[size=14.666666984558105px]Litchi displays:Gound elevation 68m(16m above[size=14.666666984558105px] first waypoint)
[size=14.666666984558105px]30+16=46m
[size=14.666666984558105px]I agree with that.

[size=14.666666984558105px]Now going down:
[size=14.666666984558105px]Starting point alt 68m, start flying at 30m(Waypoint1). Litchi shows waypoint 1 alt 30m,
[size=14.666666984558105px]Finish point alt 53m Litchi shows finish waypoint alt 14m
[size=14.666666984558105px]Litchi display: Ground elevation 53m (16m below[size=14.666666984558105px] first waypoint)
[size=14.666666984558105px]30-16=14m
[size=14.666666984558105px]I agree with that.

[size=14.666666984558105px]My question is: at the end of the down leg my Phantom will be at 14m or 30m over the ground?

Prtobably none of the above, as the elevations recoded in Google Earth and those registered by the aircraft will most likely bear no resemblance to each other. The aircraft barometer is not that accurate.

I have to admit that I had a hard time following that (hey, it's been a long day). But the important thing to remenber it that waypoint altitude is relative to the take-off point altitude, so in theory if you're taking off at 50m above sea level and your weightpoint is set for 30m then the P4 will be flying at 80m above sea level at that point.

It's very important to get POI heights right too. I wanted to fly through a wind farm recently. Turbine prop hubs are 80m off ground and the props have a 55m diameter. So to clear the turbine I need at least 80m+(55m/2), or 107.5m? So flying at 120m high would have cleared it, right? Wrong! I must have taken off 40m down the hill, as when the P4 said it was flying at 120m it was looking straight at the hub. It would have been a massacre if I set up a mission based on a flying height of 120m through the wind farm...