Photogrammetry and ground-based laser scanning: assessment of metric accuracy of the 3D model of Pozzoveggiani church

Among the plenty of works so far presented on the use of laser scanning for cultural heritage survey, it can be noted that some geometric related issues have been not yet solved for. Most effort has been spent to achieve visually pleasant 3D models, mainly for VR applications, but only a few works addressed the metric and geometric accuracy of generated 3D models. According to such remark, this paper deals with the comparison between digital photogrammetry and laser scanning techniques applied to the survey of the outside of the ancient church of Pozzoveggiani, located in the sourrounding of Padua (Italy). To this aim, the work was carried out according to three different stages. Firstly a classic topographic/photo-grammetric survey was performed: digital color images were acquired with a prosumer digital camera and then post-processed using a photogrammetric bundle adjustment and a commercial software (PhotoModeler). In the second stage the church was fully surveyed with a terrestrial laser scanner, Mensi GS100 and the corresponding model was generated employing Polyworks as modeling software. Then, in the third stage the metric accuracy of both the 3D models has been assessed by comparing the coordinates of common points. To this end a set of check points were measured on the walls of the church by a total station, in order to provide a common reference system. Comparisons were based on natural targets only, in order to evaluate the performance of the whole 3D modeling pipeline, from data acquisition to model generation, when working in a worst case scenario, i.e. when no retroreflective targets can be used.