3D modeling of roman bridge by the integration of terrestrial and UAV photogrammetric survey for structural analysis purpose

The 3D survey of the masonry bridges is rather complex and may require the integration of terrestrial and aerial surveys. In fact, in order to perform the survey of the superstructure of a bridge, the photogrammetric survey may be realized by the use UAV (Unmanned Aerial Vehicle) since it allows acquiring all the details of the upper part of the bridge. Indeed, especially the extreme lateral parts of the bridge cannot be performed through a traditional terrestrial survey. In addition, the UAV photogrammetry allows speeding up and optimizing work. As regards the terrestrial survey, instead, it has the advantage of being able to use highly performing optics and cameras (high resolution of the sensor, stabilized optics, etc.). However, these types of sensors are quite heavy and, in general, could not be mounted on an aerial platform on commercial and low-cost drones. In any case, beyond the payload of common commercial drones at low cost, there is also the problem that the digital cameras mounted on the UAV platforms cannot observe the arches of the bridge from the bottom upwards by low-cost tools. Therefore, a simple way to build a unique 3D model consists in the integration of terrestrial and aerial surveys; in this way, using a suitable procedure, sensor and software based on the Structure from Motion (SfM) and Multi View Stereo (MVS) approaches, it was possible to build detailed, precise and textured three-dimensional models of structures, such as the buildings, historical artefact, bridges etc. In this paper, a case study concerning the construction of a three-dimensional model according a photogrammetric method of a Roman bridge is discussed. In particular, the bridge taken under investigation, belong to the Cultural Heritage, is called "San Cono" and is located in south of Italy. After built the 3D model of masonry bridge (3D point cloud and 3D mesh), it was identified a special procedure that allowed to obtain the model of the bridge suitable for a structural analysis within of dedicate software.