Abstract
AbstractThe current clearance inspection of a railway tunnel is mostly limited to extracting and analyzing 2D cross sections. A novel clearance inspection technique has been introduced to generate the high-resolution digital elevation model (DEM) of a railway tunnel surface (bare lining) from terrestrial laser scanning (TLS) data. In this process, the tunnel boundary points and the upper boundary points of the inner rail are extracted from tunnel point clouds. By using these two boundary point groups, multimodel fitting is used for the estimation of the horizontal and vertical alignments based on the random sample consensus (RANSAC) algorithm, and the final alignments are determined using a global optimization based on piecewise fitting. The theoretical surface of a curved tunnel is reshaped into a developable surface using a new coordinate system named tunnel stationing coordinate system (TSCS). The stationing and cross-sectional horizontal datum (SCHD) and the overbreaking and underbreaking vertical dat...
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