Ultralight UAV for steep-hill archaeological 3D survey

The role of drones is becoming increasingly im-portant within current 3D survey methodologies. Their flexibility of use and the ability to acquire images from inaccessible viewpoints make them a critical instrument in multiple fields of applica-tion at both urban and architectural scales. This success is mainly due to the progressive devel-opment of technology, including data acquisition sensors, flight systems, and data processing pro-grams. The Cultural Heritage domain is one with the most widespread and massive applications. Be-sides, due to the RPAS regulations in Italy, drones less than or equal to 250 g have seen a consid-erable expansion in use in recent years. The im-proved quality of the cameras and the recent introduction of flight planning has made them proper for photogrammetric applications. Recent research reports experiments in the architectur-al and archaeological domains aimed at verifying the metric reliability of the acquired data compared with active instruments. In archaeological surveying, drones can cover large complex areas quickly, minimizing shadow areas concentrated in the crests of walls. The case study presented is the Canossa Castle, a medieval archaeological complex close to Reggio Emilia and extended on a steep hill with rocky spurs. The work describes integrating GNSS, 3D scanners, and ultralight RPAS photogrammetry, gathering multi-scale geometric information. The integration between the different surveying techniques allowed to plan different verification moments on the metrological reliability of the multi-resolution model. Al last, the data acquired made it possible to produce complete architectural and urban representations, improving the knowledge needed to prepare the virtual reconstruction of the entire complex area.