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inaccurate DSM elevations

This past week I flew a Phantom Vision 2+ using the iOS Capture App at three different locations each on a different day.  At each location I mapped approximately 100 acres averaging four to six flights.   After post processing, 12 out of 15 flights have elevations in the DSM that are roughly 600’ above the actual ground elevation.  I first recognized this when merging projects, the first three flights had proper elevation while the last three did not creating an obvious terraced appearance.m I always had 7+ satellites and calibrated my compass as required.  Does anyone have an idea what could cause this and is there a solution?

Dear Jarrett,

It is strange that this happened only for some flights. Were all parameters the same for all flights? (Capture App always used, same hardware)

The DJI GPS records the altitude as 0 where it is turned on, i.e. the altitude is relative. The Pix4D Capture app uses the phone’s reading of its own current altitude to give an absolute altitude and writes this in the EXIF file. This could cause this kind of issue. 

When merging the projects, make sure to add Manual Tie Points that are common to both projects. This helps the software and reduces the likelihood of this terraced appearance.

Best regards,