Morphological Analysis for Architectural Applications: Comparison between Laser Scanning and Structure-from-Motion Photogrammetry

Terrestrial laser scanning (TLS) and structure-from-motion photogrammetry (SfM) can both provide dense and accurate point clouds. Therefore, they can be used to perform a morphological analysis of the façades of a masonry building, which relies on evaluation of the differences between the point cloud and a reference regular surface fitted to it. To compare TLS and SfM performance in morphological analysis, multimodal surveys were carried out on the square cross-section, 48-m-high Garisenda Tower in Bologna, Italy (reference surface: plane), and the circle crosssection, 42-m-high Caorle's leaning bell tower in Venice, Italy (reference surface:moving cylinder). The results show that the TLS- and SfM-based morphologies are qualitatively the same, and the relative differences are lower than 10%-20% under the condition that the viewpoint positions (VPs) are optimal. Also, the overall geometries are correctly described by both the techniques. The main conclusion is that, if no particular constraints exist (e.g., unavoidable suboptimal VPs, night surveys are needed, or trees hide the surface), TLS and SfM have similar performance in morphological analysis.