These are black and white orthophotos created from frames of the “ALIFOTO 1975” plane flight. To make this product, around 11,000 frames of the “ALIFOTO 1975” plane flight were scanned in black/white with an average scale of 1:15,000. The source material is arranged in rolls of negative on transparency film. The entire project area was divided into blocks and aerial triangulation was performed on each individual block, to facilitate calculations and to allow for better control; accurate of the results. The subdivision into blocks took into account the topography of the terrain, the analogue flight plan and, above all, the belonging of the frames to the same roll, to ensure uniformity; in the transition from scanning to triangulation, without interruptions or seams, and in the subdivision of the final orthorectified product. The scanning of all the negatives took place with a photogrammetric scanner with geometric accuracy of +-2 microm and high radiometric performance with a dynamic range of 12bit and a "density range" of 3.4D or greater. The scan was performed at a true optical resolution of 1200dpi, resulting in a pixel size of the digital image of approximately 30cm. Individual scans were saved in 8-bit TIFF format. The orthorectification operation was performed using the Lombardy Region DTM as a digital model of the terrain with a sampling step of 20m.
