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Z-axis offset caused by Inaccurate camera calibration

Hello Support Team and Pix4Dmapper Users,

In recent months we frequently faced Z-axis offset (elevation shift) on check points
while using PPK images of senseFly eBeeX + AeriaX and we were told it is because of the camera calibration error , we normally had around one GSD accuracy for XY.

We arranged a test field with area around 60 ha with 6 GCPs and flew 3x GSDs
with each following combination

eBeeX+AeiaX @ GSD=3cm, 6cm & 10cm
eBeeX+SODA @ GSD=3cm, 6cm & 10cm
eBeePlus+SODA @ GSD=3cm, 6cm & 10cm

for each GSD we see a shift on check points with no GCP
but in combined 3 GSDs in eBeeX with both cameras we had much better results
but still have a slight shift (it is not in random range with + - signs)

From accurate combined process, we copied the optimized values of
f, Px, Py, R1, R2, R3 and saved in a new camera in database
and reprocessed the inaccurate GSD project with selecting it
and changed the calibration settings to
Method= Alternative, Internal= None, External=All
Then Rematch and Optimize to fix basic parameters
Sometimes It highly improves the results, sometimes not
the behavior is inconsistent and uncontrollable

I think until last year we did not have this problem
and we had accurate flights with PPK
It became a nightmare for us

Any other users have ever faced this?

Awaiting for your kind solution or response

Regards
Mehdi

1 Like

I am facing exactly the same issue as well for my Sony ILCE camera with 16mm Emount lens flying on a quadcopter. An additional observation in my case is that when flying my quadcopter at lower speed like ~5m/s the z accuracies are very good but for higher speeds like ~12-14m/s there is a random offset observed in the Z axis error values. And, this offset seem to have a proper relation with the optimized focal length number observed in the quality report indicating that the calibration may have been inaccurate.

I want to understand what could be the cause for such inaccuracies only in the z-axis and how can it be corrected?