Documentation and analysis of extremely subtle ageing changes are being carried out in seven series of 3D measurements over a period of thirty months. Currently (July 2019) we are approaching the end of this process. It is therefore time to present the preliminary results of our work (the first publication on this subject will be published in a month’s time as a result of the SPIE Optical Metrology, Optics for Arts, Architecture, and Archaeology VII conference in Munich: R.Sitnik, K. Lech, E. Bunsch, J. Michoński, “Monitoring surface degradation process by 3D structured light scanning”, SPIE Optical Metrology, Optics for Arts, Architecture, and Archaeology VII, Munich 2019).
Based on the analysis of data from five series of measurements, each of which included the collection of three-dimensional documentation for twelve 12 X 12 cm fragments of the façade, we can conclude that the innovative documentation method developed by us allows us to track even the smallest changes in the shape of the examined surface. Based on measurements made with the three-dimensional scanning method with structural lighting, with a spatial resolution of 2,500 measurement points per mm2, we are able to obtain data with an error of no more than 13 µm (0.013 mm). Due to the need to take these measurements in dark conditions for proper contrast, the scans are always performed at night (fig. 1). Thanks to the solutions developed by scientists from the Faculty of Mechatronics of the Warsaw University of Technology, completing forty measurement sequences making up the documentation of each of the fields measuring 12 x 12 cm takes only 25 minutes and is carried out in automatic mode. It was also possible to significantly automate the process of processing the results obtained in this way.
One of the measurement fields is located on the south elevation of the palace, at the foot of the tower. The sandstone fragment of the pilaster has had horizontal dispersions visible for several years. Precise observation, possible thanks to the new documentation method, makes it possible to determine whether cracks are growing and whether micro-chipping appears on their edges (fig. 2, 3). In the near future, the results of our measurements will be consulted with conservators responsible for the state of preservation of the palace elevation.
The acts of vandalism we wrote about a year ago are no longer as intense as they were, but unfortunately, they are still happening: the markers used for positioning and matching measurements are still being thoughtlessly pulled out of the walls of the palace. Therefore, further development of this technology may have to include not only increasing the capacity to analyse the data collected, but also designing markers that are more difficult to destroy by vandals.
LIST OF ILLUSTRATIONS:
1. Automated system for three-dimensional measurements with structural lighting, developed to measure the façade of the Wilanów Palace (left). The system during night work on the façade in April 2019 (right).
2. One of the measurement fields located on the south elevation of the palace in Wilanów. On the right-hand side, in the close-up, markers for comparing measurements, protected by special plastic caps can be seen.
3. Visualisation of the analysis results of the sample field geometry (this is the field described in the previous photo).