PSI - Issue 64

A. Di Benedetto et al. / Procedia Structural Integrity 64 (2024) 2254–2262 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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ratio. In the calculation of the y i coordinate, a multiplication by -1 was applied to avoid obtaining a specular point cloud. The z i coordinates represent the distance of each point from the interpolated circle. 4. Results The point cloud in the tunnel was divided into 5 meter-long boxes, which were derived from the offset of the roadway axis polyline, extracted using intensity values. The tunnel’s point cloud was then divided into eighteen boxes (Figure 3), each of which was roto-translated with respect to the local reference, as described in the methods section.

Fig. 3. Point cloud overlaid with boxes.

The point clouds of the boxes where subsequently subjected to radiometric correction using the methodology outlined in Section 3.1. The radiometric correction was performed by applying the "near range" function (f 1 ) equation (1), as the distance between the tunnel intrados and the MLS trajectory is less than 10 meters. The radius and coordinates of the center of the interpolated circumference were calculated for each box using the RANSAC method. Figure 4 illustrates the points of a generic box (black dots), projected onto the plane (y', z') and the interpolated circumference (red line).

Fig. 4. Point cloud of the generic box projected onto the (y', z') plane with the interpolated circumference overlaid in red, with the blue point locating the center of the circumference.

With the coordinates of the center and the radius of the circumference, the unrolling algorithm calculated the plane coordinates of the point cloud of the generic box. Subsequently, these point clouds were automatically filtered to remove objects that do not belong to the tunnel intrados such as the lighting system, cables, and signage. The condition of the intrados surface was evaluated by calculating the roughness. A sphere radius of 20 cm was