Unwrapping a Baroque Masterpiece: A Planar Representation for the Apse of Santa María del Temple in Valencia

Abstract. This study presents a workflow for the documentation and morphological analysis of curved frescoed surfaces, combining terrestrial laser scanning (TLS) with computational imaging techniques. The case study focuses on the apse of the Church of Santa Mar´ıa del Temple in Valencia (Spain), decorated in 1770 with Palladian motifs. The objective is to produce a planar and interactive representation of the surface, overcoming the operational limitations of traditional Reflectance Transformation Imaging (RTI). The methodology employs a Trimble TX6 TLS to rapidly record a high-density point cloud within minutes. The dataset is then processed using open-source software tools (CloudCompare, MeshLab, Blender, Relight) to reconstruct a detailed mesh and generate a high-resolution normal map (NM), which is transferred onto a low-poly model. A digital RTI dome consisting of 49 spotlights is built in Blender, producing a sequence of rendered images that are subsequently processed to create an easy-to-use Virtual RTI (VRTI). This approach enables the clear identification of degradation features and subtle morphological irregularities that are not easily detectable through conventional methods. The proposed workflow proves to be effective for qualitative analyses, simplifying targeted conservation interventions, especially in architecturally complex contexts where traditional techniques are unfeasible or hardly applicable. V-RTI thus represents a valuable complementary strategy for non-invasive cultural heritage (CH) diagnostics.