Towards a short-range laboratory for testing the accuracy of terrestrial 3D laser scanning (TLS) technologies

Abstract

Laser Scanning is a 21st century surveying technique used to generate high density and point cloud data in 3D for surveying, mapping and monitoring purposes, for example rock mass movement in mining. For high precision and accurate work, the instrument must be used correctly and with regular calibration and checks to ensure that it constantly performs according to expectations and manufacturer specifications. The aim of this research was to develop a short-range scanning laboratory for testing the accuracy of terrestrial laser scanning systems for rock engineering applications. This research was based on methods used by previous researchers in testing the accuracy of the instrument and the development of a suitable facility for such testing. The procedure used in developing the short-range testing facility included selecting an appropriate venue of size and shape that suits the requirements for a short-range laser scanning laboratory. This was followed by the construction of the master control beacon and creation of additional scan set ups in order to capture all the points in the facility. Targets were strategically placed on the wall and roof of the laboratory in order to determine the centre point coordinate of each target. A Leica Total Station TCR 1201+ and Trimble S6 Total Station were used to establish accurate coordinates for the control beacon and the targets respectively. Thereafter, the scanning of the targets was carried out using a FARO Focus XD 130 terrestrial laser scanner. Comparisons were performed using the coordinates from the terrestrial laser scanning and those of the Total Station to examine the point accuracy of the scans. The results from the comparison between the scanner coordinates and the total station coordinates showed that the FARO Focus laser scanner performed within manufacturer specifications but not always. This implies the instrument is capable of generating accurate point and reliable cloud data that can be used for the purpose of monitoring underground rock mass movements. Errors regarded mistakes in the final analysis occurred as a result of target design (in terms of size and orientations) and oblique lines of sight.