Document Type : Original Research Paper
Authors
Department of Geomatics, Faculty of Civil Engineering, Babol Noshirvani University of Technology, Babol, Iran
Abstract
Background and Objectives: Using UAV photogrammetry for corridor mapping in areas with significant differences between their longitudinal and lateral dimensions reduces the geometric strength of the imaging network and introduces numerous challenges. These challenges in UAV photogrammetry lead to increased project time and costs, as well as higher errors in triangulation calculations. Several parameters—such as the distribution and number of ground control points, camera calibration methods, the number of flight strips, and the use of precise camera positions obtained from the Global Navigation Satellite System (GNSS)—affect triangulation accuracy. This study examines the impact of these parameters on triangulation accuracy in corridor areas.
Methods: The evaluation of parameters affecting triangulation accuracy was conducted on two corridor areas with lengths of two and a half and five kilometers. In this research, three parameters—distribution and number of ground control points, camera calibration methods, and photogrammetry software—were examined on a single flight strip, and multiple flight strips were used solely to evaluate the impact of the number of flight strips on triangulation accuracy. The results were assessed based on the root mean square errors of planimetric and altimetric errors at the check points. In this study, the photogrammetry software Pix4D and Agisoft Metashape were used for triangulation calculations.
Findings: The evaluation results regarding the impact of the distribution and number of control points showed that using eight control points—distributed as follows: two points at the beginning, two points at the end, two in the middle of the corridor (all opposite each other across the width), and two additional points in between—can improve triangulation accuracy compared to other configurations. Additionally, using the self-calibration method for the camera in triangulation calculations yields more accurate results than using pre-calibrated cameras. Moreover, employing more than one flight strip increases the accuracy of triangulation results.
Conclusion: By appropriately designing ground control points throughout the entire corridor and applying the self-calibration method for camera calibration—without relying on precise image center coordinates—it is possible to achieve an accuracy of less than one meter for producing engineering maps at scales of 1:500, 1:1000, and 1:2000, with contour intervals of 0.5 meters, 1 meter, and 2 meters, respectively.
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© 2025 The Author(s). This is an open-access article distributed under the terms and conditions of the Creative Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)
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