mbuonanno
Second Officer
Italy
Offline
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Hi SUYDESA,
I haven't installed the new update yet, but I think that RELATIVE HEIGHT is the difference in height between the take-off point and the mapped area, whereas RELATIVE ALTITUDE is the height above Home Point (i.e. the take-off point) at which the drone flies.
Unfortunately DJI uses five terms: Absolute altitude, Relative altitude, Mission Altitude, Flight Altitude and Relative Height.
In the P4RTK User manual you can read:
"There are two kinds of altitudes displayed in the DJI GS RTK app, absolute altitude and relative altitude.
Absolute altitude: The geographical attribute, in relation to longitude and latitude.
Relative altitude: The altitude data of the operation tasks relative to the Home Point. In the same operation, the absolute altitude for the same point during the operation will vary when taking off from locations with different elevations"
and also...
"Relative Altitude: The relative height between the takeoff point and the operation area. The actual operation height is the aircraft height minus the relative height. NOTE: Make sure to set the correct relative height to ensure the results contain appropriate overlap rates."
More detailed info (and a graph) can be found in the P4RTK FAQ page, "Software" section, Question 20 "In what cases do I need to adjust the relative height value?"
Moreover in the DJI Terra FAQ page, "Flight and aerial images" section (see Question 5 and 6):
"The RELATIVE HEIGHT, in the advanced settings, is the elevation of the take-off point with respect to the mapped area. The MISSION ALTITUDE is the height of the drone with respect to the same area, and it is also the reference value with which the soil sampling distance (GSD) is calculated."
I think there is a misuse of the terms Altitude and Height. In aeronautics ALTITUDE (ALT) is "the vertical distance of an object measured from mean sea level (MSL)", whereas HEIGHT is "the vertical distance of an aircraft above whatever SURFACE (buildings, mountains, a lake, etc.) (height above ground level or height AGL)".
Cheers,
Maurizio
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