## 4 Discussion  
Historical aerial photographs are an invaluable cultural resource, allowing us to study information on land cover and land use changes with high spatial and temporal resolution. The scanning of such datasets is the first step of the digitization process. To obtain the highest accuracy, photogrammetric scanners should be preferred to consumer-grade scanners, even if they are much cheaper instruments. Photogrammetric scanners, in fact, have been manufactured to minimize scanning artifacts and the distortion or loss of spatial and radiometric resolution during digitalization [17]. Digital copies of analog photos made by consumer-grade scanners provide insufficient resolution and geometric accuracy. In processing the camera's interior orientation while measuring the fiducial marks, it provided lower measurement accuracy between the 2.5-5.5 pixel size (35-77 \(\upmu\)m) compared to measurements on the photogrammetric scanner data of a 0.2-1.1 pixel size (3-15 \(\upmu\)m), which implicates less accurate measures of 5-10 times on the digital images. The successive bundle adjustment and AT are affected by errors in image measurements. First, unchanged terrain details were measured in the field using GNSS technology and used as GCPs and CPs. Typically, to collect 4D ground control points, fast and cheap methods consisting of geo-referenced maps or orthoimages are used to derive planimetric coordinates and DSM or trigonometric fix points for altimetric coordinates [24]. Topographic surveying methods, which are more time-consuming, are less often performed for this purpose [22]. Point coordinates measured with the GNSS method provided reliable reference data with excellent accuracy to perform some analyses to check the quality of products from historical images. In the AT process, better results were obtained for the photogrammetric scanner than for the consumer-grade scanner (sigma naught of 8.4 \(\upmu\)m and 0.6 px with respect to 12.8 \(\upmu\)m and 0.9 px, respectively). For the RMSE of check points, an accuracy of \(X\) = 13, \(Y\) = 10, and \(Z\) = 12 cm in Metashape was obtained compared to the RMSE of \(X\) = 43, \(Y\) = 23, and \(Z\) = 23 cm in Inpho software. Applying self-calibration to both datasets in Metashape improved the results obtained in the AT process by 0.4 pix for sigma in the photogrammetric set and 0.2 pix for sigma in the regular set. The RMSE of check points with camera self-calibration improved results significantly for the consumer-grade dataset. The total XYZ RMSE was reduced from 54 cm in Inpho to 36 cm in Metashape. It means that a camera calibration for computing additional parameters like B1, B2 (affinity and skew-non-orthogonality), K1, K2, K3 (radial distortion coefficients), P1, and P2 (tangential distortion coefficients) effectively improves the quality of measurements in images scanned with a consumer-grade scanner. In the analyses of the DIM results, it was shown that the photogrammetric scanners allow us to derive more accurate point clouds with respect to consumer-grade scanners. Based on the results, it should be concluded that regular scanners do not have enough scanning quality to ensure high-resolution accuracy and geometric precision when working with digital forms of analog aerial images, in contrast to specialized photogrammetric scanners. This result has been also shown by [19], underlying that desktop scanners used in the photogrammetry process require complex and unique additional calibration. The