Handling hundreds of aerial images without ground references: archaeological photointerpretation in the era of digital photogrammetry,

Each archaeological context or region often requires adaptations of consolidated techniques and practices to better overcome local obstacles and boost peculiar potentials. Cases are where the view-from-above is impeded, restricted or limited by national laws, absence of infrastructures, inaccessibility (or unavailability) of photographic archives. Whether one prefers (or is allowed) to approach the above exemplificative issues with the exclusive or complementary use of manned aircrafts, remotely piloted aerial systems or historical archives, the management of the acquired dataset (or the new data generated from its processing) is not trivial and may even generate pitfalls, if not properly handled. Examples in this paper, presented with the goal to highlight potential issues and the proposed solution in different contexts, are synthesized as follow: high resolution RPAS photogrammetric model of mountainous and mostly inaccessible landscapes without the possibility to employ or measure ground control points (because of the bushy/forested nature of the area, the difficulty of carrying bulky GNSS or EDM devices); georeferencing of historical photographs in a quickly changing environment; mosaicking hundreds of single frames of buried archaeological features where no reference items (i.e. buildings, cross-roads, field boundaries,...) could be identified.