Uncertainty assessment of TLS distance deviations evoked by material and incidence angle

Abstract

Terrestrial Laser Scanners (TLS) are increasingly being used in the field of engineering geodesy. The 3Dpointaccuracy achievable with state-of-the-art TLS is in the low millimetre range and manufacturers of TLSeven state ranging precisions down to the submillimetre range. This encourages investigations on suspected systematic effects that might influence the uncertainty of TLS distance measurements. The commercial launch of geodetic multi stations - these instruments combine the capabilities of total stations (TS) and TLS - allow a new approach to check the performance of TLS distance measurements, particularly with respect to the material being scanned and the laser’s angle of incidence on the scanned object. Such a methodology, referred to asROSIAM, for evaluating TLS distance measurements has been developed by the research unit of Engineering Geodesy at TU Wien. The basic principle is the direct comparison of TLS distances with reference distances obtained by an instrument with higher accuracy.The objective of this work is to determine and quantify sources of uncertainty in the ROSIAM methodology andto create a comprehensive uncertainty budget for the derived differences between TLS distances and reference distances. Variance-covariance propagation and Monte Carlo simulation are used as computational methods to determine the combined effect of all known sources of uncertainty on the distance differences. An essential step for this is the development of a network transformation model to establish a spatial relationship between the measurands of TLS and reference instrument, which can be placed arbitrarily to each other.In this thesis, the uncertainties of distance differences are determined for incidence angles ranging from 0 to60 gon and for seven different materials. Significant disparities in distance differences are found between all materials for a majority of the incidence angles studied. This leads to the conclusion that systematic effects underlie the observed distance differences.It is also ascertained that there are no significant differences in the uncertainties of the distance differences with regard to material and incidence angle. Therefore, a single value of 0.2mm can be used as standard uncertainty for all TLS distance differences. However, this value is limited to the ROSIAM method, the materials investigated and the range of incidence angles investigated.Based on the results, the ROSIAM methodology is deemed sensitive enough to investigate suspected systematic effects in TLS distance measurements of multi stations.