Strumenti e metodi geomatici per lo studio di un’antica cava etrusca

Il rischio idrogeologico in Italia è diffuso in modo capillare. Diversi sono i fattori naturali che predispongono il nostro territorio a crolli in roccia, frane e alluvioni. La prima causa è senza dubbio la conformazione geologica e geomorfologica, caratterizzata da un’orografia giovane, quale quella alpina, e da rilievi in via di sollevamento. Per questo motivo, le tematiche legate allo studio degli ammassi rocciosi sono da sempre di primaria importanza. I metodi tradizionali di rilievo di una parete in roccia, per l’analisi successiva di rischio crolli, prevedono l’azione di un geologo specializzato direttamente in quota. È chiaro come questa operazione non sia semplice e richieda molte competenze multidisciplinari. Con questa attività si è voluto studiare l’utilizzo di metodi geomatici per rilievi geotecnici, in particolare l’uso della fotogrammetria (aerea e terrestre) e del LiDAR (Light Detection and Ranging). La parete oggetto di studio, che si trova all’interno del parco archeologico di Baratti e Populonia, ricopre molta importanza dal punto di vista storico e culturale, essendo essa un’antica cava di epoca etrusca

AUTOMATIC IN-SITU SELF-CALIBRATION OF A PANORAMIC TLS FROM A SINGLE STATION USING 2D KEYPOINTS

Terrestrial laser scanner (TLS) measurements are unavoidably affected by systematic influences due to internal misalignments. The magnitude of the resulting errors can exceed the magnitude of random errors significantly deteriorating the quality of the obtained point clouds. Hence, the task of calibrating TLSs is important for applications with high demands regarding accuracy. In recent years, multiple in-situ self-calibration approaches were derived allowing the successful estimation of up-to-date calibration parameters. These approaches rely either on using manually placed targets or on using man-made geometric objects found in surroundings. Herein, we widen the existing toolbox with an alternative approach for panoramic TLSs, for the cases where such prerequisites cannot be met. We build upon the existing target-based two-face calibration method by substituting targets with precisely localized 2D keypoints, i.e. local features, detected in panoramic intensity images using the Förstner operator. To overcome the detriment of the perspective change on the feature localization accuracy, we estimate the majority of the relevant calibration parameters from a single station. The approach is verified on real data obtained with the Leica ScanStation P20. The obtained results were tested against the affirmed target-based two-face self-calibration. Analysis proved that the estimated calibration parameters are directly comparable both in the terms of parameter precision and correlation. In the end, we employ an effective evaluation procedure for testing the impact of the calibration results on the point cloud quality

Towards System Calibration of Panoramic Laser Scanners from a Single Station

Terrestrial laser scanner measurements suffer from systematic errors due to internal misalignments. The magnitude of the resulting errors in the point cloud in many cases exceeds the magnitude of random errors. Hence, the task of calibrating a laser scanner is important for applications with high accuracy demands. This paper primarily addresses the case of panoramic terrestrial laser scanners. Herein, it is proven that most of the calibration parameters can be estimated from a single scanner station without a need for any reference information. This hypothesis is confirmed through an empirical experiment, which was conducted in a large machine hall using a Leica Scan Station P20 panoramic laser scanner. The calibration approach is based on the widely used target-based self-calibration approach, with small modifications. A new angular parameterization is used in order to implicitly introduce measurements in two faces of the instrument and for the implementation of calibration parameters describing genuine mechanical misalignments. Additionally, a computationally preferable calibration algorithm based on the two-face measurements is introduced. In the end, the calibration results are discussed, highlighting all necessary prerequisites for the scanner calibration from a single scanner station