# From Analogue to Digital Photogrammetry: Documentation of Padise Abbey in Two Different Time Stages
## 6 Conclusions  
Due to the photogrammetric surveys carried out in different time stages, it is possible to create 2D and 3D results which help to study, examine, and explore different states and different conditions of cultural heritage objects. Those multitemporal results are comparable and could be valuable for architects, restorators, and conservators. Capturing of the images for photogrammetric processing during analogue era was a highly sophisticated work with a high-quality metric camera. Every capture of an image must be precisely planned. The number of the images was a topic. The storing medium was expensive, and the photogrammetric processing took much longer with higher number of images. On the other side, nowadays, using a (sometimes low-cost) non-metric digital camera, it is possible to capture many images without any additional cost. The preparation is thinner. Processing of the images is much faster using structure from motion method and it is possible to gain a variety of two-dimensional and three-dimensional results. Using modern structure from motion method, it is also possible to re-process digitized analogue images. Although the datasets are inherently different, to achieve respectable accuracy, the pipeline of processing could be similar for digital and analogue datasets. Even though it is possible to process the digitized analogue data using modern methods, which were designed originally by computer vision science, for analogue data restoration, digitization, and successful processing, it is essential to keep the knowledge about fundaments of the analogue photogrammetry. In 1991, [PERSON] carried out photogrammetric survey of the south wall of Padise Abbey. Using an analogue metric camera UMK 6.5/1318, he and his team captured 12 images in six stereo-pairs. After more than 25 years, the glass plate negatives and partial documentation were found, and the negatives were digitized and re-processed using SfM method. The relative orientation was computed, scaled, adjusted, and the accuracy was checked on measured distances between markers and measured distances between each image of each stereo-pair. Then, the textured 3D model, point cloud, and orthophoto were generated. The new photogrammetric survey with a digital camera was carried out in 2017 after the renovation of the south wall of Padise Abbey. The images were processed using SfM method as well. The model was georeferenced to the model made by re-processing to obtain the same coordinate system. As control points and check points, we used markers carved into stones in 1991 and significant features of stones of the south wall. The RMSE of differences in coordinates in X axis was 0.004 m and in Z axis 0.009 m (XZ plane is parallel to the wall). The results of the processing were also a textured 3D model, point cloud, and orthophoto. The different states of Padise Wall between 1991 and 2017 are possible to explore and present on comparison of results made by re-processing of images and new survey. In our opinion, an overlay of two orthophotos offers the easiest comparison of different states. The overlay is an easily understandable result, could be exported to the widely used formats, could be a source for CAD drawing, and could be a data for GIS and BIM systems. On the other hand, operating point cloud requires some knowledge and proper software. As was shown, using Cloud/Cloud and Cloud/Mesh comparison, it is possible to determine differences concerning which stones of the wall are preserved, and which stones of the wall are an outcome of renovation. Differences under chosen threshold (0.05 m) were considered as points belonging to the preserved stones and an overlay with orthophoto was carried out. The overlay showed that the points fit to the manually created boundary. The semi-automatic or automatic gathering of semantic data from Cloud/Cloud or Cloud/Mesh comparison is going to be a topic of the future research. From the point clouds were created textured 3D models.