Measurement planning for circular cross-section tunnels using terrestrial laser scanning

Recent years have witnessed a growing use of terrestrial laser scanners to determine the geometry of tunnels, although the companies that perform this task do not, as a rule, apply a methodology that enables them to optimize results. We describe an approach to scanning circular cross-section tunnels which takes account of several factors that affect the quality and cost of scanning, namely, tunnel dimensions, scan density, footprint size, incidence angle and scanner location. This method determines the maximum scan distance and the angular sampling interval that yield a pre-determined level of accuracy while minimizing working time.

► We describe an approach to scanning circular cross-section tunnels.
► Scanner position, scanning density, incidence angle and footprint size are analysed.
► The optimum angular interval and maximum scan distance are calculated.
► Very small angular intervals are not recommended.
► The location of the equipment is crucial.