Accuracy Assessment of a Photogrammetric UAV Block by using Different Software and Adopting Diverse Processing Strategies

UAVs systems are heavily adopted nowadays to collect high resolution imagery with the purpose of documenting and mapping environment and cultural heritage. Such data are currently processed by programs based on the Structure from Motion (SfM) concept, coming from the Computer Vision community, rather than from classical Photogrammetry. It is interesting to check whether some widely accepted rules coming from old-fashioned photogrammetry still holds: the relation between accuracy and GSD, the ratio between the altimetric and planimetric accuracy, accuracy estimated on GCPs vs that estimated with CPs. Also, not all the SfM programs behave in the same way. To face the envisaged aspects, the paper adopts a comparative approach, as several programs are used, and numerous configurations considered. The University of Pavia established a test field at a sandpit located in the Province of Pavia, in northern Italy, where several flights were performed by the multi-rotor HEXA-PRO UAV, equipped with a 24 MP Sony Alpha-6000. One of these blocks has been extensively analysed in the present paper. The paper illustrates the dataset adopted, the carefully-tuned processing strategies and BBA (Bundle Block Adjustment) results in terms of accuracy for both GCPs and CPs.