Reading the Absolute/Relative Accuracy Portion of the QR

PIX4Dmapper PIX4Dmapper Questions/Troubleshooting
1

Can someone please help me to understand how to read this, in the simplest of terms?

I just need to know how accurate I am, within absolute and relative accuracy.

I’ve tried to research everything but I still can’t make heads or tails of this.

Thanks ahead of time

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2

For absolute accuracy, you will need to add checkpoints.

3

Thank you, but that’s not what I’m asking. I just want to know how to read the numbers in the report. Where can I exactly see how accurate I am, how do I get to that number, and how to I quantify that number.

Again, I’m not seeking to accomplish more accuracy on this already done mission. I’m just looking for insight on how to read this portion of the report, in simple terms. I know about GCP’s, I know about relative accuracy, I know about absolute accuracy. I’m just seeking some translation of raw numbers here.

Thanks

5

Hi,

General information about Absolute and Relative accuracy can be found in this article.

Here is some information that you could find helpful about absolute and relative geolocation in the Quality Report:

Absolute Geolocation Variance

(from here)
This table displays the percentage of geolocated and calibrated images with a geolocation error in X,Y,Z within a predefined error interval. There are ten predefined intervals between -1.5 and 1.5 times the maximum accuracy Amax of all images. If the percentage of images with an error lower than -1.5 × Amax or higher than 1.5 × Amax is big, the Accuracy values might not have been set correctly. Verify if the Accuracy of the image geolocation and the GCPs need to be adjusted.
This table also evaluates the quality of the image geolocation. A high percentage of images with a high error may indicate:

  • Noise in the GPS device.
  • Poor synchronization between the GPS device and the camera.
  • Errors in the geotagging process.

More information about the specifications of this table can be found in this article.

Relative Geolocation Variance

(from here)
This table displays the percentage of geolocated and calibrated images with a Relative Geolocation Error between -1 and 1, -2 and 2 and -3 and 3. A high percentage of images with a Relative Geolocation Error lower than -3 or higher than 3 may indicate an incorrect value for the Accuracy of the image geolocation (given by the user). Verify if the Accuracy of the image geolocation and the GCPs need to be adapted.
In projects without GCPs:

  • If less than 99.6% of the geolocated and calibrated images have an error between -3 and 3, then the geolocation Accuracy might be overestimated. Try to increase the value of the geolocation Accuracy.

More information about this table’s specifications can be found in this article.

In simple terms, based only on the onboard GNSS receiver, the accuracy of your images’ geotags is in the range of approximately 1 meter (in all directions).

However, we strongly suggest using GCP in order to make sure that there are no shifts in your dataset.

I hope this information helps you.

Cheers