Architectural heritage 3D modelling using unmanned aerial vehicles multi-view imaging

Abstract

Today, Architectural Heritage 3D models are created using Unmanned Aerial Vehicles (UAV) imagery and processing through Computer Vision (CV) methods. They are becoming more acceptable as reliable sources for study, documentation, diagnostics, intervention planning, monitoring, and management decision-making. The Deir-e-Kaj caravanserai, located in Qom, Iran, is a massive and half-destroyed architectural heritage that belongs to the Seljuk era. The obstructed access due to illegal deep excavations and the extensive demolished structure did not allow for a complete mapping using traditional and terrestrial techniques. Considering the condition and vulnerability of the artifact, it looks necessary to use a safe, non-destructive, and remote method for 3D documenting. The literature review shows in most of the research UAVs are used for acquiring nadir images, which are combined with the terrestrially acquired data for complete 3D modelling. In this case, a multi-view UAV imaging strategy is considered for the as-is 3D modelling of Deire-e-Kaj. Three different imaging angles are designed and used to carry out the comprehensive and all-needed data acquisition. The nadir images are acquired to cover the plan and enclosure, and the horizontal and oblique images cover the façades and interior spaces of the artifact. Adopting a suitable photogrammetric process based on the SfM workflow allows for obtaining an accurate, high-quality, and textured 3D model of the caravanserai. Accuracy evaluation of the result using Ground Control Points shows a total accuracy of ±1 cm. This study demonstrates the efficiency of multi-view UAV photogrammetry as a rapid, safe, and precise method to create a complete 3D model of massive, hard-to-access, and vulnerable Architectural Heritage.