Self-calibration of terrestrial laser scanners: selection of the best geometric additional parameters
Systematic errors are present in laser scanning system observations due to manufacturer imperfections, wearing over time, vibrations, changing environmental conditions and, last but not least, involuntary hits. To achieve maximum quality and rigorous measurements from terrestrial laser scanners, a least squares estimation of additional calibration parameters can be used to model the a priori unknown systematic errors and therefore improve output observations. The selection of the right set of additional parameters is not trivial and requires laborious statistical analysis. Based on this requirement, this article presents an approach to determine the best set of additional parameters which provides the best mathematical solution based on a dimensionless quality index. The best set of additional parameters is the one which provides the maximum quality index (i.e. minimum value) for the group of observables, exterior orientation parameters and reference points. Calibration performance is tested using both a phase shift continuous wave scanner, FARO PHOTON 880, and a pulse-based time-of-flight system, Leica HDS3000. The improvement achieved after the geometric calibration is 30% for the former and 70% for the latter.