Selected aspects of geometrical analyses of surfaces measured using terrestrial laser scanning (TLS)

Abstract

Modern measurement technologies are widely used for the monitoring and determination of surface deformations. One more frequently used measurement technology is terrestrial laser scanning (TLS), which provides quasi-continuous information about the tested surface in the form of a point cloud at a given resolution. At the same time, TLS is based on measuring the distance in a given direction, thanks to which we can obtain a high precision of measurement, often compared to tacheometric measurements. This paper presents a study on the determination of surface flatness parameters extracted from a point cloud. It takes into account the roughness characteristics of the different structures on the measured surfaces and analyzes them using the most popular algorithms for determining the distance of points from the reference surface. Additionally, the review presents the issue of expanding selected surfaces onto a plane to analyze their geometric parameters, and thus to determine the deformation. The applied solution can be used to monitor the deformation of objects such as tunnels and interiors of collectors or large-diameter downpipes, the shape of which is similar to a cylinder surface. Thanks to the expansion of the cylinder surface into a plane, it is possible to perform a comprehensive analysis of surface deformation, and not only selected fragments in the form of sections. The conducted analyses show the great potential of data obtained using terrestrial laser scanning, when an appropriate procedure and data processing method are applied. This paper focuses on two types of studies; the study of surface flatness and analysis of the deformation of cylindrical surfaces. These types of studies are extremely useful in assessing the technical condition of structures, especially in studying the deformation of structures built underground (tunnels, passages, warehouses), where the loads from the surrounding earth are significant.