We are modelling tree canopy using a DJI Phantom that was flown with an active RTK. The area that we are flying has an elevation (terrain / bare earth) of between 71-77m AMSL.
The photogrammetry in Pix4D Mapper is showing values that comprise the ground are 43m, so substantially below what the known elevation of the area is. Those values are not anomalous, they are representative of the ground at large. Does anyone have any idea what might be the issue here?