08/09/2026
What is RMSE in Photogrammetry?
If you work with drone photogrammetry, you’ll often see the term RMSE – Root Mean Square Error.
But what does it mean or tell you about the quality of your survey?
The RMSE is a statistical measure of how closely your model agrees with known or surveyed positions.
For example, a Ground Control Point (GCP) is tagged in the imagery and assigned coordinates. Once processing is complete, the software compares the modelled position against the known position and calculates the error.
Check Points (CPs) work in a similar way, but they provide an independent assessment of the finished model, because they haven’t been used to constrain the processing.
How is RMSE calculated?
Imagine a CP has been surveyed by GNSS: Known: E 500.000 m | N 200.000 m | Z 100.000 m Model: E 500.012 m | N 199.994 m | Z 100.008 m
The residuals are, Easting: +0.012 m, Northing: −0.006 m, Height: +0.008 m
RMSE squares the errors, calculates their mean, then takes the square root: RMSE = √[(e₁² + e₂² + … + eₙ²) / n]
Why square the errors? Because positive and negative errors shouldn’t simply cancel each other out.
What does RMSE tell you?
If your independent CP assessment produces: Horizontal RMSE = 0.018 m, Vertical RMSE = 0.025 m.
This indicates how closely the model agrees, statistically, with the independently surveyed points.
But an RMSE of 25 mm does NOT mean every point is accurate to ±25 mm. Some points may have less error, while others may have considerably more.
That’s why RMSE should be considered alongside individual residuals, maximum errors, error distribution, outliers, systematic bias and the quality of the survey control.
The important takeaway
A good-looking orthomosaic doesn’t automatically mean you have an accurate survey. Rather than asking: “How accurate is the drone?” A better question is: “How was the accuracy of the final dataset assessed and demonstrated?”
Professional photogrammetry isn’t just about collecting data. It’s about being able to demonstrate the quality of the results.