The results that follow were obtained by a company that specializes in tunnel surveys and inspections by using their most accurate laser instrument. In this set-up, the laser scanner is mounted on a vehicle with its rotating axis parallel to the tunnel axis.
The vehicle must travel at a speed as constant as possible because the scanner, once started, keeps spinning at a constant speed and it cannot be stopped until the vehicle reaches the end of the area to be surveyed. Therefore, the scanner projects a spiral onto the tunnel walls, whose pitch depends on the speed of the vehicle.
The survey refers to a two-lane road tunnel in which the roadway enclosure (walls and ceiling) was completely tiled. One lane at a time was closed to traffic. The following figures compare side-by-side the crack surveys as carried out by Tonon USA and by means of the results provided by LiDAR.
Tonon USA survey of roof. Notice perfect representation of square tiles.
LiDAR survey of roof. Notice the wavy representation of square tiles, which reflects a wavy 3D model of an otherwise flat roof.
LiDAR survey of the entire the tunnel
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