Accuracy Reporting

PIX4Dmatic
1

I’m having a hard time understanding how to determine the overall accuracy of a project in Pix4Dmatic. For example, I’d like to be able to tell my surveying department that the dataset is accurate to within ±2 cm horizontally and ±5 cm vertically.

I’ve been using the Accident Reconstruction aerial crash scene as a sample dataset. I understand that checkpoints need to be added to evaluate accuracy. In my project, I used CP1, CP2, and CP5 as ground control points (GCPs), and CP4, CP6, and CP7 as checkpoints.

How do I correctly determine the project’s absolute accuracy from this setup? For instance, if a cellphone had landed on the ground at the crash site, how precisely could I identify its location based on my processed data?

Thank you for your help!
accident_training-quality_report_2025-07-28_16-52-39.pdf (3.7 MB)

2

Hi Tommy,

The easiest way is to look at the checkpoints in the Quality Check at the beginning of the quality report. In the report you provided, the mean RMS position error is 0.032 ftUS. The RMS is the root mean square and it is a type of average that indicates the magnitude of the values, regardless of their signs. In your case, it would be safe to assume that any give point is within 0.032 ft.

3

Hi Mike, Thank you for getting back to me so quickly. I feel like this is very high for a photogrammetry accuracy even with PPK applied to the imagery. That is sub cm precision. Am i missing something projects are typically 1-2 times as accurate as project’s GSD?

4

The accuracy is a function of your ground sampling distance (GSD). You can expect 1-2 times the GSD for the horizontal and 2-3 times GSD for the vertical. Your GSD is 0.023 ftUS. You likely flew the drone very low but the data acquisition was good and the project processed well. I feel confident in the results.