Digitisation and Georeferencing of an Oversized Historical Map of the Bailiwick of Neuland (Winsen/Luhe) using Structure-from-motion (SFM) Photogrammetry

Abstract The study of historical maps has gained significant importance in recent years due to their ability to shed light on past geographical and topographic landscapes, since they serve as crucial sources for understanding past conditions. They do not only provide insights into the geography and topography during the time they were created but also allow for studying long-term changes over time. In this study, an oversized historical map of the Bailiwick of Neuland from the years 1780 to 1790 was discovered in the archives of the municipal building office in Winsen an der Luhe, Germany. The map, measuring approximately 5 m × 2 m, was digitised by photogrammetric methods and subsequently georeferenced. The process involved photographing the map with two different cameras and two UAV systems at the Geodetic Laboratory of HafenCity University Hamburg. This allowed to generate a high-resolution orthophoto from each data set. The resulting orthophoto achieved a pixel size of 0.2 mm, ensuring detailed representation of the map. To ensure accuracy, the best photo block was scaled in a bundle block adjustment using control points with an accuracy of 1 mm and scale bars with an accuracy of 0.1 mm. Georeferencing of the historical map was conducted using current digital orthophotos of Lower Saxony with a resolution of 20 cm. A third-degree polynomial transformation was applied during georeferencing, resulting in mean residuals of 2.5 m at the ground control points. This process ensured that the historical map was accurately aligned with the current digital orthophotos, allowing for precise spatial referencing.