Photogrammetric state of degradation assessment of decorative claddings: the plasterwork of the Maidens' Courtyard (The Royal Alcazar of Seville)

Abstract

Highlights: The photogrammetric survey demonstrates to be a potential tool in the preventive conservation of ancient plasterworks. The high-precision 3D model allows the study and quantification of alterations (e.g. fissures, deformations, and loss of mass or polychromies). The virtual model and the analysis performed with CloudCompare software provide fast, accurate and accessible results to experts in the field. Abstract: Previous studies and documentation about the state of conservation of architectural or decorative elements are crucial for heritage managers, technicians and researchers to succeed in the maintenance and preservation of the heritage. In this sense, hand tracings, digital drawings, or photographs have traditionally been the methods for alteration and sample mapping. In spite of their effectiveness, these methods have some disadvantages, such as the need for more precision in terms of location, dimensions, quantification and types of alterations. By contrast, high-resolution three-dimensional (3D) models allow us to analyse decorative ancient plasterworks with great precision, offering considerable advantages over traditional tools for heritage documentation. To facilitate stakeholders’ work and enhance the quality of data collected, this work proposes the use of photogrammetry as a tool for the documentation of polychromed ancient plasterworks, taking the upper frieze of the access door to the Charles V ceiling room in the Royal Alcazar of Seville as a case of study. Thus, the work methodology applied has shown several advantages over previous methods. On the one hand, it was possible to obtain a 2D planimetry from the 3D model; this is an essential step for those responsible for heritage, especially in reports prior to restoration interventions. On the other hand, the 3D model created enables present alterations identification, the location of fissures and cracks in their three dimensions (opening, length and depth), deformations measurement and control, the quantification of mass or polychrome loss, and the detached elements digital reconstruction. In this way, highprecision digital results are quickly obtained and accessible to all the experts involved in the heritage conservation and maintenance plan.