A simplified procedure of metrological testing of the terrestrial laser scanners

Abstract

This paper presents a simplified test procedure of the terrestrial laser scanners (TLS) accuracy investigation by the general criteria of the ISO17123 standard. The proposed procedure covers investigation, analysis and accuracy estimation of the TLS system in the controlled environmental conditions. This procedure is mainly developed based on the model of a system calibration and network design procedures. Metrological Laboratory of the Faculty of Civil Engineering in Belgrade is customized for TLS testing. The accuracy investigation of a commercial TLS has been performed. The accuracy of the resulted point cloud, which is indirectly represented by the coordinates of the acquired control points, is determined. Beside the analysis of the residuals of the 3D spatial transformation, the analysis of the true and the measured distance differences is also performed. The results show that these two approaches give the statistically same uncertainty indicators. Precision of the target recognition and influence of the unlevelled point cloud to the TLS centering error is also analyzed. Normality tests are used to determine whether a data set is well modeled by a normal distribution or not before testing of hypothesis for the variances. By varying the number of the control and check points it is shown that increasing the number of the control points more than three well distributed is not relevant for significantly higher transformation accuracy. On the basis of the conducted spherical orientation analyzes it can be concluded that the global orientation of the error vectors follows the laser beam direction due to relatively short distances. The most important result related to investigated TLS is that this particular sensor must be used only by indirect georeferencing experiment design.