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ABSTRACT:The task of conservation and management of cultural heritage is quite central in Italy, which lists a high number of beautiful architectures. A quick and precise survey may be requested in case of calamity. In the present paper, the most commonly used survey techniques are discussed, focusing on their applications for the conservation of the artistic heritage in case of emergency. Particular attention is given to Unmanned Aerial Systems (UAS) photogrammetry and its potentiality in obtaining good results in terms of speed, cheapness, precision and accuracy, assuring at the same time the safety of the operators in critical situations (e.g. natural disasters). A case study, realized at the Castle of Casalbagliano (Alessandria, Italy), is discussed. Different image block configurations and acquisition geometries (nadiral and oblique images) have been exploited, with the aim of defining useful guidelines for emergencies UAS survey of partially collapsed structures. An application to a significative case study is introduced.

An optimized planning and realization of the survey, coupled with well thought-out processing, allows obtaining good quality results, while guaranteeing a reasonable use of resources and time. It represents a benefit for both operators and end-users. The former can save time and acquire smaller datasets to process, while the latter can invest their resources better. These goals are even more important in case of an emergency, because the circumstances can quickly change, causing risk to both people and goods. The paper examines the possibility of using Unmanned Aerial Systems (UAS) photogrammetry for 3D modelling in such scenario, focusing on finding a compromise between the final accuracy and the requested processing time. An experimental test has been conducted over the Castle of Casalbagliano, a damaged structure located near Alessandria (Piedmont, Italy), simulating a postemergency scenario. Several processing strategies have been tested to define a workflow useful in this kind of situations. The quality of the different processing has been evaluated in terms of both residuals of the bundle block adjustment and quality of the generated dense point cloud, compared with a reference Terrestrial Laser Scanner acquisition. Finally, the possibility of publishing the obtained 3D models on the web has been exploited too.

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