Study on 3D rail approximation methods using terrestrial laser scanner point clouds

Abstract

In the three-dimensional design and digital twin construction of railway infrastructure, the track center-line serves as a crucial spatial reference. This study proposes and evaluates methods for approximating the three-dimensional rail geometry based on centroids extracted from rail parts in point clouds obtained by Terrestrial Laser Scanners (TLS). Eight different approximation schemes were designed by combining three elements: the choice of parametric variable (Y-coordinate or curve length), fitting method (least squares or RANSAC), and direction-wise application (common or separate treatment of directions). These schemes were quantitatively compared in terms of approximation accuracy and error structure. Results indicate that using curve length as a parameter stabilized variations in the X direction, and RANSAC showed high adaptability in the horizontal direction. However, in the vertical direction, RANSAC tended to exclude structurally significant changes. Furthermore, the evaluation also revealed the impact of TLS error structures and alignment procedures, emphasizing the importance of both method selection and measurement conditions in constructing three-dimensional track centerlines.