Accuracy assessment in Structure from motion 3D reconstruction from UAV-born images: the influence of the data processing methods

The evolution of Structure from Motion (SfM) techniques and their integration with the established procedures of classic stereoscopic photogrammetric survey have provided a very effective tool for the production of three-dimensional textured models. Such models are not only aesthetically pleasing but can also contain metric information, the quality of which depends on both survey type and applied processing methodologies. An open research topic in this area refers to checking attainable accuracy levels. The knowledge of such accuracy is essential, especially in the integration of models obtained through SfM with other models derived from different sensors or methods (laser scanning, classic photogrammetry ...). Accuracy checks may be conducted by either comparing SfM models against a reference one or measuring the deviation of control points identified on models and measured with classic topographic instrumentation and methodologies. This paper presents an analysis of attainable accuracy levels, according to different approaches of survey and data processing. For this purpose, a survey of the Church of San Miniato in Marcianella (Pisa, Italy), has been used. The dataset is an integration of laser scanning with terrestrial and UAV-borne photogrammetric surveys; in addition, a high precision topographic network was established for the specific purpose. In particular, laser scanning has been used for the interior and the exterior of the church, with the exclusion of the roof, while UAVs have been used for the photogrammetric survey of both roof, with horizontal strips, and façade, with vertical strips.