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How to determine image geolocation accuracy

I did a PPK test last week, which didn’t yield the results I was hoping for. I used an Emlid Reach M+ on my Matrice 600 to log shutter events from my Sony A6000 mapping camera and post-processed this with raw base and rover data. After that, I geotagged the images in Pix4D prior to Step 1. I also placed 4 GCPs as checkpoints and this was the quality report:

Needless to say this is not acceptable. I posted this on a FB group and one of the users said I needed to change the accuracy of the photos in the Images Properties Editor. By default, it’s set to 5m/10m… and he said I should change it to 0.05m (since every picture does indeed have a very high accuracy). Painful process, since I had to do that manually for every picture, but okay. And this is the quality report after re-running Step 1:


I can’t really explain my feelings about this, but it feels like cheating or something. Besides that, the suggested 0.05 value for accuracy isn’t based on anything. The question here is twofold:

  • How does Pix4D process this image accuracy?

  • What is a realistic value, so that the quality report is trustworthy and can be shown to customers?


And I just did another test, whereby I changed the checkpoints to 3D GCPs… take a look at the absolute vertical error. I just don’t understand how this works…