Data quality assurance for hybrid and panoramic scanners via self-calibration

Quality assurance (QA) is a crucial process to ensure the maximize accuracy of the data delivered to client. Equipped with many moving parts whose relative positions can change over time depending on use, handling frequency and care, the QA is essential for TLS. Furthermore, with rapid and dense three-dimensional (3D) data collection ability, TLS has gain interest for many accurate 3D applications (e.g. industrial surveying, deformation measurement and reverse engineering). The QA for TLS measurement can be performed through calibration procedures, whether via component or system calibrations. Due to the non-affordable facilities and tools by most TLS users required by component calibration, this study focussed on the latter approach which only requires a room with appropriate targets. By employing optimal network configuration, system calibration was performed through self-calibration for hybrid (Leica ScanStation C10) and panoramic (Faro Photon 120) scanners. Four calibration parameters (e.g. constant range (a0), collimation axis (b0), trunnion axis (b1) and vertical circle index (c0) errors) were derived from 138 well-distributed targets in a laboratory with dimensions of 15.5m (length) × 9m (width) × 3m (height). For accuracy assessment purpose, fifteen test points are established at calibration field using photogrammetric technique. Those test points then were used to graphically and statistically evaluate the improvement in accuracy between TLS raw and calibrated data. As expected, the outcomes of statistical analyses have indicated an accuracy enhancement, for both scanners, respectively of 11% for Leica ScanStation C10 (1.7mm) and 50% for Faro Photon 120 (1.8mm) scanners.