Combined 360 video and uav reconstruction of small-town historic city centers

Small-town historic urban environments increasingly face different pressures that may prevent their future sustainability. To promote a recovery plan for those centers, an interdisciplinary methodology is needed to orient future actions toward innovative solutions. However, the development of such a plan needs the definition of a dedicated methodology to drive the definition of recovery actions. A key role is the possibility of low-cost methods for mapping and classifying the built heritage. Both ground and aerial (UAV) solutions can be used to create 3D city models for further classification and analysis. However, integrating those two data in small city centers poses specific challenges. This paper presents a combined approach using ground and aerial (UAV) data to comprehensively reconstruct a part of a small-town city center. Ground data are video acquired with 360 degrees (spherical) cameras. Previous works proved 360 degrees videos can reconstruct with good metric accuracy and complete building facades of historic city centers. The combined reconstruction is tested in the so-called "Casa Teatro", an abandoned building in the city center of Vogogna, a small town in the Ossola Valley (Northern Italy). The results of the combined image orientation are validated by using ground truth data (Check Points) acquired with a total station. In contrast, the final 3D model reconstruction results are compared with a laser scanning acquisition of the building to evaluate the accuracy and completeness of the photogrammetric point cloud. In addition, matching among 360 degrees frames and UAV frames is studied by analysing connectivity graphs.