CALIBRATION OF A RIEGL LMS-Z420i BASED ON A MULTI-STATION ADJUSTMENT AND A GEOMETRIC MODEL WITH ADDITIONAL PARAMETERS

The paper presents the calibration and analysis of a terrestrial laser scanner Riegl LMS-Z420i. Two different calibration fields were scanned with this laser scanner from different positions. The calibration fields are equipped with signalized targets to be measured within the laser scanner point cloud interactively or automatically. The measured spherical coordinates (distance, horizontal angle and vertical angle) were used as observations in a multi-station adjustment, equivalent to a photogrammetric bundle adjustment. In extension to the basic geometric model a set of additional parameters was used, which were determined in a self-calibration procedure. These additional parameters are partly derived from well-known error sources of geodetic instruments as axes errors or axes eccentricities and partly taken from the literature, where the calibration of other laser scanners is already described. The calibration results (parameter values, standard deviations, significance), which were calculated from the observations of both calibration fields are analyzed and compared. The combination of the adjustment procedure with variance component estimation allows for the separate assessment of the precision of the different types observations (distance, horizontal angle, vertical angle). Thus, the precision improvement of the adjusted observations as result of a stepwise addition of calibration parameters is investigated. As object point coordinates were handled as unknowns within the adjustment, their standard deviations were calculated and analyzed. It could be shown that the use of additional calibration parameters has the potential to increase the object point precision.