ConNext-2021

38 Preliminary study for the development of a three ‐ dimensional monitoring procedure for dimension changes using 3D metrology KEYWORDS: photogrammetry, point clouds, distance comparison, monitoring, 3D metrology. Dimensional changes of historical objects caused by environmental influences are a phenomenon frequently encountered in conservation. The resulting damages are manifold and often severe. Hence the question arises if it would be possible to observe dimensional changes and their development three-dimensionally with suitable monitoring, to enable taking preventive measures against this damage in time? As part of a bachelor thesis, this study deals with the process of photogrammetry and its suitability for three-dimensional monitoring. The starting point was the archaeological find of the Schöningen spears and the idea to develop a monitoring for possible dimensional changes of these fragile finds inside of their museum. On the one hand, this requires a technical procedure that does not need expensive equipment, can be carried out by trained laypersons (conservators) and offers a high degree of accuracy to detect changes in the millimetre range. Based on this, I have dealt with the creation of 3D point clouds using the technique of photogrammetry. The original images for the point clouds were generated with standard digital SLR cameras and were loaded in a low-cost software designed for this purpose. The focus of this research was the comparison of different computed distances from photogrammetrically generated point clouds of the same object. The main goal was to investigate whether point clouds from different photo series of one object show a sufficiently high similarity to each other. By comparing the computed distances from different point clouds of the same object, generated at different moments, a potential dimensional change may become clearly visible. The point clouds can be coloured for better differentiation. Therefore, dimensional changes could be revealed virtually and without physically handling the object. The scheme illustrates the process, using an oak ashlar as an example (see figure). The possibilities of current photogrammetry software and commercially available camera equipment are suitable for generating point clouds with a high degree of accuracy if used correctly. Further research will need to show whether the effort for implementation is feasible for the work of a conservator and if the process remains time- effective for its potential gain. matthias.vogel[at ]stud.hawk.de