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In our paper we will present results of an on-going project connected with monitoring the condition of 12 fragments of the Museum of King Jan III’s Palace at Wilanow (Warsaw, Poland) building facade by 3D structured-light scanning method. During 30 months, 7 series of three-dimensional measurements have been planned. In each of the twelve elevation fragments, chosen by the conservation and architecture departments as particularly interesting, an area of 120 mm x 120 mm was scanned with 2500 points/mm2 resolution. This article describes the methodology of the measurement process, the hardware setup developed especially for this purpose, as well as the data processing path and analysis algorithms. In addition to having such accurate measurement data, we must still be able to match the measurements carried out in the same place at intervals of several months. For this purpose the areas of interest were marked with special aluminum targets, embedded with three intersecting planes. The algorithm of their detection, analysis and use for aligning data from subsequent measurement series is discussed. A portable SLS 3D-measurement head with two cameras, integrated with linear drive has been developed for scanning purposes and adopted to use in outdoor condition. The 3D scanner has a measurement volume limited to 45 mm x 50 mm x 10 mm for a single scan, due to high-resolution requirements. In less than 25 minutes, 40 measurements are acquired at various positions, covering the entire area, with the support of a controlled linear stage stand. Individual scans are pre-aligned with limited accuracy and then fitted using the Iterative Closest Point algorithm. The final representation of each fragment is a cloud of points with color containing more than 200 million 3D measurement points. We present the results of 3D measurements and a proposition of a monitoring procedure for assessing the change in 3D surfaces over time. |
