UAS-based photogrammetry of cultural heritage sites: a case study addressing Chapel of Espírito Santo and photogrammetric software comparison

The cost-effectiveness of unmanned aerial systems (UAS) makes them suitable platforms to survey cultural heritage sites. Developments in photogrammetry provide methods capable to generate accurate 3D models out of 2D aerial images. Considering the involved technologies, the purpose of this paper is to document the Chapel of Espirito Santo: a very relevant monument for Vila Real (Portugal) that is currently located at the campus of the University of Tras-os-Montes and Alto Douro. The UAS based aerial imagery survey approach is presented along with photogrammetric process to build chapel's 3D model. Moreover, two photogrammetric software were compared - Pix4Dmapper Pro and Agisoft Photoscan - in terms of modelling accuracy and functionalities ease of use.