Terrain Following - ASL and Flight Route Altitude

[Mark107]

Ok.. I'm totally confused about the settings in a Mapping mission for the ASL/ALT differences. I think I understand how to set my flight height based on ALT by setting the "Flight Route Altitude". But I'm not quite sure I understand the "Target Surface to Takeoff Point" setting. Or when setting it to ASL, I'm seeing the Flight Route Altitude Ellipsoidal Height at a -56.7'. (I understand the ellipsoidal height generally does not match the actual ground surface but it's still confusing to me. And the Flight Route to Target Surface is confusing as well. Could anyone tell me where would I go to get some explanation of these settings? I don't want to look like an idiot to anyone other than my wife for very long..

 

[Mike@Dragonfly]

From page 82 of the manual:

The starting plane of the flight route altitude.

• Relative to Takeoff Point (ALT): the altitude of the aircraft relative to the takeoff point. It is recommended to use this option for aerial mapping operations. Then, Target Surface to Takeoff Point will appear. Target Surface to Takeoff Point = the altitude of the target surface - the altitude of the take-off point.

• ASL (EGM96): the altitude of the aircraft relative to the EGM96 geoid. Flight Route to Target Surface will appear. Flight Route to Target Surface = the altitude of the flight route - the altitude of the target surface

It sounds like the target surface to takeoff point would be used if you are taking off from a much different altitude than you are mapping at.