Ground control, checkpoints, and accuracy

Topic 3: UAS Flight Planning

Published

October 26, 2026

Outline

What flight GSD buys you: the floor it sets on horizontal and vertical accuracy, and why you rarely stand on it
Ground control versus checkpoints: fitting the map versus judging it
RTK and PPK direct georeferencing, and what still needs a ground point
Systematic error: doming, why it beats random noise, and how to detect it in a report
Reading the Agisoft and WebODM reports side by side
The level of detection: deciding with arithmetic whether a flight can count trees or quantify micro erosion

Lecture

Lecture Slides: Ground Control, Checkpoints, and Accuracy

Supplemental materials

ASPRS Positional Accuracy Standards for Digital Geospatial Data, Edition 2, Version 2 (2024) (American Society for Photogrammetry and Remote Sensing 2024): Addendum V is the UAS chapter; Section 7.16.1 covers reporting with fewer than 30 checkpoints
GNSS field protocol: the base station and checkpoint procedure used at the Lake Wheeler flight
Sanz-Ablanedo et al. 2018 (Sanz-Ablanedo et al. 2018): the GCP density and checkpoint-overestimation numbers
Stott et al. 2020 (Stott et al. 2020) and Zhang et al. 2019 (Zhang et al. 2019): the modern RTK/PPK versus GCP evidence
James and Robson 2014 (James and Robson 2014) and James et al. 2020 (James et al. 2020): doming and its mitigations
Wheaton et al. 2010 (Wheaton et al. 2010) and Anderson 2019 (Anderson 2019): uncertainty in DEM differencing

Assignment

Assignment 3B: Validate the Lake Wheeler flight: establish the base coordinate three ways, evaluate the flight’s orthomosaic and DSM against the withheld checkpoints, and rule on what the flight can measure. See the assignment page for data, submission, grading, and the due date.

References

American Society for Photogrammetry and Remote Sensing. 2024. ASPRS Positional Accuracy Standards for Digital Geospatial Data, Edition 2, Version 2. American Society for Photogrammetry; Remote Sensing. https://publicdocuments.asprs.org/PositionalAccuracyStd-Ed2-V2.

Anderson, Scott W. 2019. “Uncertainty in Quantitative Analyses of Topographic Change: Error Propagation and the Role of Thresholding.” Earth Surface Processes and Landforms 44 (5): 1015–33. https://doi.org/10.1002/esp.4551.

James, Mike R., Gilles Antoniazza, Stuart Robson, and Stuart N. Lane. 2020. “Mitigating Systematic Error in Topographic Models for Geomorphic Change Detection: Accuracy, Precision and Considerations Beyond Off-Nadir Imagery.” Earth Surface Processes and Landforms 45 (10): 2251–71. https://doi.org/10.1002/esp.4878.

James, Mike R., and Stuart Robson. 2014. “Mitigating Systematic Error in Topographic Models Derived from UAV and Ground-Based Image Networks.” Earth Surface Processes and Landforms 39 (10): 1413–20. https://doi.org/10.1002/esp.3609.

Sanz-Ablanedo, Enoc, Jim H. Chandler, José Ramón Rodríguez-Pérez, and Celestino Ordóñez. 2018. “Accuracy of Unmanned Aerial Vehicle (UAV) and SfM Photogrammetry Survey as a Function of the Number and Location of Ground Control Points Used.” Remote Sensing 10 (10): 1606. https://doi.org/10.3390/rs10101606.

Stott, Eilidh, Richard D. Williams, and Trevor B. Hoey. 2020. “Ground Control Point Distribution for Accurate Kilometre-Scale Topographic Mapping Using an RTK-GNSS Unmanned Aerial Vehicle and SfM Photogrammetry.” Drones 4 (3): 55. https://doi.org/10.3390/drones4030055.

Wheaton, Joseph M., James Brasington, Stephen E. Darby, and David A. Sear. 2010. “Accounting for Uncertainty in DEMs from Repeat Topographic Surveys: Improved Sediment Budgets.” Earth Surface Processes and Landforms 35 (2): 136–56. https://doi.org/10.1002/esp.1886.

Zhang, He, Emilien Aldana-Jague, François Clapuyt, Florian Wilken, Veerle Vanacker, and Kristof Van Oost. 2019. “Evaluating the Potential of Post-Processing Kinematic (PPK) Georeferencing for UAV-Based Structure-from-Motion (SfM) Photogrammetry and Surface Change Detection.” Earth Surface Dynamics 7 (3): 807–27. https://doi.org/10.5194/esurf-7-807-2019.