CALIBRATION OF TERRESTRIAL LASER SCANNERS FOR THE PURPOSES OF GEODETIC ENGINEERING

In order to achieve the results that meet specifications of a given project the knowledge of the accuracy of the surveying equipment is inevitable. Standard calibration models and procedures exist for all traditional geodetic and photogrammetric instruments, and they should also be developed for terrestrial laser scanners (TLS), a new surveying technique. This is especially important for using TLS in high-precision applications, like engineering surveys and deformation measurements. The development of such models and procedures, available to users, is carried out within a research project at the Geodesy Division of the Royal Institute of Technology (KTH). Three scanners - Callidus 1.1, Leica HDS 3000 and Leica HDS 2500 (the latter is owned by the Division) - have been investigated at the specially established indoor 3D calibration field, following the common routine. The main interest was to investigate the systematic instrumental errors. The knowledge of these errors is rather limited due to the proprietary design of the scanners. Our approach was to first perform scanner self-calibration, assuming that the systematic instrumental errors were the same as those in the total station, and then to compare the distances, horizontal directions and vertical angles derived from the scanning with the true ones in order to reveal the possible presence of some non-modelled systematic trends. We have found a significant vertical scale error in the scanner Callidus 1.1. We have also investigated the target coordinate accuracy, stability of the range measurements over time (range drift) and angular accuracy and precision. The results are believed to give a good insight into the inner working of TLS and a grounded estimate of their performance. They also provide a good base for comparison of different scanning systems and the development of standardized calibration models and procedures for TLS.