Why we use GCP's

#1

Here is a quick visual of why I will not stop using GCP’s even though I started using PPK. This illustrates a standard mission vs a PPK/GCP mission. The non-GCP is lower in the blue areas and higher in red areas. Overall it is a balance error of 0.4ft (12.1cm), which shows how much adjustment the local benchmark GCP’s move everything. The verification on the PPK/GCP surface was staked in the field to +/- 1.5in (3.8cm). The main point of this is to display relative vs absolute local accuracy. I know that the PPK/GCP surface is tight and you can see the shift of cut/fill as you move from the single-point calibration of the standard map from the center outward. Basically this means that the whole site is tilted down to the east on the standard flight according to DJI’s GPS and barometer. This is an effect of the barometer heating up and as the flight commenced from west to east the elevations reported started to drop. Last note is the PPK mission without the GCP’s was right in between the two at about a 5.5cm error.

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#2

Michael, what average accuracy do you get with non-ppk data but with well distributed GCPs? Is 4cm unrealistic?

#3

I think 5-6cm is pretty typical. So beyond just the accuracy increase I went from about 15 down to 5 gcps on this site and still have a little better accuracy.

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