Challenges in 3D integrated surveying of complex historic sites: The case of Santa Maria della Steccata (Parma – Italy)

This article addresses the challenges of conducting integrated 3D surveys of complex historic architecture, focusing on the documentation and modelling of the Basilica of Santa Maria della Steccata in Parma (Italy). The Basilica’s impressive scale, rich decorative features, and complex architectural layout – including a network of secondary spaces and attics accessible only through narrow, meandering paths – posed significant challenges for the survey. To overcome these obstacles, an integrated approach combining Terrestrial Laser Scanning (TLS), Close-Range Photogrammetry (CRP), Spherical Photogrammetry (SP), and UAV Photogrammetry was employed. The article outlines the planning, execution, and processing phases of the survey campaign, with particular emphasis on the methodological issues involved in merging data from multiple sources in such a constrained and heterogeneous environment. In this context, the article introduces and evaluates an ICP-assisted Bundle Block Adjustment (ICP-BBA) strategy designed to improve CRP- and TLS-derived models, demonstrating its effectiveness in enhancing local consistency in areas prone to residual misalignments. In addition, the performance of SP is examined under varying spatial conditions, highlighting its potential both as a supplementary method for areas with restricted accessibility and as a stand-alone alternative in specific use cases.