This paper looks at changes over time in the construction procedure of ceilings of cross-in-square churches, one of the most common architecture in the Middle Byzantine period (9th-12th centuries), focusing on the three-dimensional characteristics of all churches within
Abstract. The use of Structure-from-Motion algorithms is a common practice to obtain a rapid photogrammetric reconstruction. However, the performance of these algorithms is limited by the fact that in some conditions the resulting point clouds present low density. This is the case when processing materials from historical archives, such as photographs and videos, which generates only sparse point clouds due to the lack of necessary information in the photogrammetric reconstruction. This paper explores ways to improve the performance of open source SfM algorithms in order to guarantee the presence of strategic feature points in the resulting point cloud, even if sparse. To reach this objective, a photogrammetric workflow is proposed to process historical images. The first part of the workflow presents a method that allows the manual selection of feature points during the photogrammetric process. The second part evaluates the metric quality of the reconstruction on the basis of a comparison with a point cloud that has a different density from the sparse point cloud. The workflow was applied to two different case studies. Transformations of wall paintings of the Karanlık church in Cappadocia were analysed thanks to the comparison of 3D model resulting from archive photographs and a recent survey. Then a comparison was performed between the state of the Komise building in Japan, before and after restoration. The findings show that the method applied allows the metric scale and evaluation of the model also in bad condition and when only low-density point clouds are available. Moreover, this tool should be of great use for both art and architecture historians and geomatics experts, to study the evolution of Cultural Heritage.
Abstract:Digital photography is a valuable documentation technique for the preservation of a cultural heritage site because highresolution photography presents both general and detailed views of mural paintings and mural condition in a single image. Advanced digital technology is particularly helpful for preserving and restoring mural paintings given that the painting condition is recorded on high-resolution base maps shows how mural paintings are damaged by environmental stresses, mechanical damages and inappropriate treatments, among others. In addition, photogrammetric software technology is rapidly advancing and being applied to the digital documentation of mural paintings or rock art. Nevertheless, human experience and investigation of mural paintings is indispensable for recording the condition of mural paintings, and this highlights that every step of documentation conducted in situ is desirable. However, images by photogrammetric software do not show sufficient resolution because most normal portable computers used on-site are not usually sufficient. Based on our experience at the Üzümlü Church in Cappadocia, Turkey, we propose a new approach to document mural conditions in situ for preservation and restoration. Our method is based on a comparison of a non-metric but approximate high-resolution image with the actual mural paintings. The method does not require special instruments and enables digital documentation of the mural condition in situ at a low cost, in a short time frame and using minimal human resources.
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