Criteria for choosing test objects type for terrestrial laser scanners calibration

Calibration of terrestrial laser scanners allows increasing the accuracy of the obtained data in order to comply with regulatory requirements for engineering geodesy works. Two types of test objects (TCO) are used for calibration: point-based and plane-based. The aim of this work is to evaluate, summarize and classify the criteria for selecting the type and subtype of test objects for terrestrial laser scanners calibration. The arrangement of the calibration polygon is performed by taking into account the minimization of possible errors, the ability to capture the maximum field of view and range of distances, and so on. Therefore, the selection criteria are considered, systematized, and recommendations for choosing the type of TCO for practical use are developed being based on its analysis. The main criteria influencing the metric quality of calibration data are determined. The criterion of the presence of planar elements or the possibility of installing point elements is set as secondary, which is considered after evaluating all other criteria and determining the necessary conditions. The main criteria are independence from the geometric quality of surfaces; independence on the laser beam angle of incidence; arrangement of overlapping scans; the ability to calibrate both the angular and rangefinder scanner unit; the ability to link to an external coordinate system. All these criteria are considered and their impact on the calibration results are analyzed. For a more accurate assessment of the criteria, it is recommended to use Student's t-test to determine the components of systematic error that most affect the calibration data. A promising area of research has been identified - the exact spherical planar TCO centroid’s coordinates determination, which will allow one to take full advantage of both point-based and planar-based calibration objects. The scientific novelty of the study is to systematize the criteria for selecting test objects for calibration of terrestrial laser scanners and preliminary assessment of their impact on the calibration results. The obtained results allow taking into account the initial data and the existing conditions when evaluating the criteria for selecting the type of TCO for calibration in order to optimize the calibration process and further obtained data metric quality improvement.