How to Determine Survey Error for ASPRS 2024 Accuracy Reporting

This article explains how to determine and report survey error (checkpoint RMSE) in compliance with the ASPRS 2024 Positional Accuracy Standards (Edition 2, Version 2.0), including best practices from Addendum II. The survey error can then be entered into the LP360 Control Points Report opened by pressing the Accuracy Estimation tool on the Control Points tab of the ribbon.

🔍 Overview: Two-Component Error Model

ASPRS 2024 requires positional accuracy to be reported using a two-component model:

1. Product-to-Checkpoint RMSE: The root mean square error between the geospatial product and the surveyed checkpoints.
2. Survey Error (Checkpoint RMSE): The uncertainty in the coordinates of the checkpoints themselves.

Total RMSE is calculated as:

Total RMSE = √(Product RMSE² + Survey RMSE²)

✅ Best Practices from Addendum II

🧠 Step-by-Step: Determining Survey Error

1. Use Multiple Independent Observations

• Survey each checkpoint at least twice (preferably three times) with independent GNSS initializations.
• Re-initialize from different positions (≥15 ft horizontal, ≥2 ft vertical) to detect bad solutions.

2. Record Coordinate Quality Metrics

Include one-sigma standard deviation, RMSE, or CQ (Coordinate Quality) for each dimension (X, Y, Z). Example formats:

3. Minimum Observation Time

• RTK/RTN: ≥180 seconds per observation
• RT-PPP: ≥300 seconds due to convergence time

4. Point Averaging

Use a weighted mean based on CQ values to compute final coordinates. This helps eliminate outliers and improves accuracy.

5. QA/QC Procedures

• Use manufacturer-specific office software to verify field data.
• Never export directly from data collectors without QA/QC review.
• Compare surveyed coordinates with known NGS monuments to validate accuracy.

🛠️Expected Survey RMSE by Method

📋 Summary Workflow

1. Survey each checkpoint ≥2 times with independent setups.
2. Ensure ≥180 sec (RTK/RTN) or ≥300 sec (RT-PPP) per observation.
3. Record RMSE or CQ for each dimension (X, Y, Z).
4. Average observations using weighted mean.
5. Validate against known monuments (e.g., NGS).
6. Include survey error in final accuracy calculation.

References

• ASPRS Positional Accuracy Standards for Digital Geospatial Data, Edition 2, Version 2.0
• Addendum II: Guidelines and Best Practices for Field Surveying of Ground Control and Checkpoints