APPLICATION OF THE SFM APPROACH IN BUILDING 3D MODELS OF MASONRY BRIDGES USING NADIR, OBLIQUE AND ZENITH IMAGES OBTAINED FROM UAV AERIAL PLATFORM

The aim of this paper is to evaluate the possibility to build 3D models using Structure from Motion (SfM) approach and images generated by sensors mounted on UAV (Unmanned Aerial Vehicle) aerial platform. Using UAV platform it is impossible to obtain information on the intrados of the arches since the gimbal of the UAV allows camera rotation only from the nadir to the horizontal position. To overcome this limitation, a special low-cost solution was developed. This solution involved the application of a further camera (smartphone) mounted on the drone to take zenith images. In fact, the creation of a dataset of zenith images with nadir and oblique images generated by the camera supplied in the drone, suggested the possibility of building 3D models. In order to reach this aim, in the first part of the experimentation we tested the level of integration and accuracy achievable from the point clouds generated by single sensor on 3D test-field. Once verified the appropriate geometrical integration, a suitable image-based method was developed to obtain 3D models of masonry bridges. Indeed, the methodology and architecture developed was applied to create a 3D model of a masonry bridge built in the middle of 1800s and located in the south of Italy, of special architectural and historic value.