Exactly right. You are right.
Altitude measurement is the takeoff point at 0. Initially, ultrasonic altitude measurement works because it is more accurate than air pressure based. It then shows and maintains the altitude (relative to the take-off point) based on the barometric sensor above 7-10 meters.
GPS altimeter does not specify the height of the terrain either, only the drone!
You cannot measure and determine the height of the terrain !!!
A feature has been built into the Litchi-mission hub that can be turned on to adjust every point of the route to the height of the terrain (based on the google elevation map)
