Orthorectifying Library Collections of Historic Aerial Photographs for Research and Public Use

Historic orthomosaics of aerial photography have numerous research and public uses. As such, academic libraries in the USA are increasingly interested in orthorectifying their historic aerial photography collections for use in geographic information systems. How much effort this requires, and which collections constitute good candidates for processing remain unanswered, but important questions. The present study produced 11 historic orthomosaics of library collections using both ArcPro and Metashape software. Nine of these collections met a 10-m positional accuracy target using between 0.19 and 1.20 ground control points per photograph. More recently captured collections of several hundred photographs and good image quality that depicted largely urban landscapes produced the best results with the least effort. Whether a collection used fiducial markings in its alignment or the number of tie-points used per photograph in the orthorectification workflow were not found to affect results. Although limited in its scope, the present study was a first step for the library geospatial community to better understand which historic aerial photography collections are good candidates for orthorectification and how much effort it would take to perform this service.