I am confused :

1.   I am on the top of a 85 m (280 ft) building
2.   The drone takes-off and I climb it up to 20 m above my head (65 ft)
3.   My RTH is set to 40 m ( 130 ft)
4.   I outward bound the building site... I'm now flying around 105 m (345 ft) above the ground
5.   I press RTH !!!

What happens ?

Will the drone go down, come back at 40 m (130 ft) and crash into the building
Will the drone consider the controller height at the time of the taking-off and adjust upon ?
So will it climb up to 85 m (280 ft) + 40 m (130 ft) set to my RTH and land safely ?

If so, altitude is always relative to the controller, therefore, taking-off from a building, I will never know how high I did fly from the ground.

Can you explain to me ?

thx

Altitude is relative to the home point.  The drone has no way to know you are on top of a building.  If you gave the drone time to set it's starting "home" location before take off and RTH is activated, the drone will climb to 40m above its "home" starting point, fly back to directly above that point and descend to land (assuming sufficient battery power remaining, no strong wind or obstacles.)

Altitude as recorded during home point update.

So is there a way to see the actual real altitude of a flight, for instance, from sea level POV ?

thank you for your answers !

There are many apps that will show the altitude of your GPS-equipped phone.  With that information, it is a trivial task to calculate the drone altitude.   As far as I know, there is no way to do this automatically and display on the screen while flying.

Grumbleduke Posted at 12-16 16:18
There are many apps that will show the altitude of your GPS-equipped phone.  With that information, it is a trivial task to calculate the drone altitude.   As far as I know, there is no way to do this automatically and display on the screen while flying.

Grumbleduke, MANY THANKS for your help !!!