Surveying hypogeous structures: the case study of Santa Maria in Stelle in Valpantena

The hypogeous complex of Santa Maria in Stelle, known on-site as“Pantheon” and located under the parish church of Quinto in Valpantena, (Verona, Italy), is considered by scholars one of the most interesting paleochristian pictorial monuments in North Italy. Current preservation conditions are poor, affected by temperature and humidity variations which cause percolation, condensation, swelling, and efflorescence occurrences. Recurrent problematic issues during surveying operations in subterranean structures are: - necessity of instrumentation easy to handle and able to make acquisitions with the widest field of view possible, because of confined spaces often difficult to access; - remarkable wall paintings require an appropriate survey methodology through non-contact recording techniques; - the distinctive morphology of structures defined by almost uninterrupted curved surfaces makes it quite impossible to blend the geometric models detecting edges and gaps; - graphic outputs should work as a visual base for highly detailed topic representations of the state of damage. This paper reports on the techniques and procedures adopted to survey shape and dimensions of the architectural context (laser scanning), and to record the wall paintings and the floor mosaics (photogrammetry), and also on the line drawings extracted from the three-dimensional model, required as visual aids for documentation and conservation projects.