Fotografia digitale per il rilievo e la rappresentazione di dettaglio. Processi image-based per la digitalizzazione a scala sub-millimetrica

The widespread popularity of digital photography and the ongoing implementation of equipment with an extremely high processing power are among the main reasons for the extensive and popular use of image-based surveying techniques. However, especially in extreme conditions, such as activities involving the representation of sub millimetre details, the systematisation of photogrammetric applications at relatively low costs, as well as the methodological rigour imposed on the technique, generally constitute exceptions to widespread practice. Nevertheless, such circumstances are not to be considered as exceptions in the museum digitisation context, as in cases of accurate representations of numerous small artefacts; moreover, the demand also has a metrological character, as the level of accuracy of the generated models may allow experts to verify or formulate key hypotheses for the valorisation of the asset. The result is an unbalanced scenario, due to the presence of an offer limited both by application specificity and by best practices, thus creating a clear gap with the growing emerging demand catalysed by recent European actions for heritage digitisation. The reasons for a certain mistrust in the use of very close-range photogrammetry are mainly due to the necessary specialist knowledge and the costs, which are not always low, in addition to the further difficulties posed to the surveyor in situ, including the unfavourable context for complex survey campaigns. Through a necessary in-depth study of the topic and an examination of the instrumentation that can be used, the overall objective of the thesis work can be summarised as the proposal of innovative solutions for the accurate, descriptive and metric representation of objects with millimetre and sub-millimetre characteristics. The specific aim was to close a gap in the representation of objects that were too small for ordinary close-range workflows, or too large for the instruments used in precision micromechanics or microscopy of microorganisms. Hence, the key to this work lies in the systematisation of – truly accessible – approaches for the acquisition and restitution of digital models with a high power of detail, making it possible to reveal material characteristics, textures and morphologies that were hitherto not always perceptible and/or representable, and do it cost-effectively. In other words, the possibility of representing more data and on a larger scale. This aim is pursued both by codifying the use of: (i) apparatus commonly used for detailed photogrammetric applications, such as professional cameras with specific optics, but combined with ad hoc designed accessories; (ii) devices born in different fields and subsequently adapted for the purpose, e.g., portable USB microscopes. In this sense, the customisation of specifically designed accessories for the integration of USB microscopes in the photogrammetric process constitutes the innovative part of the experiment. This scenario will be dealt with by means of a compendium of ten articles written during the doctoral years, which place the purpose and results of the work in the broader context of the current state of international research and manifest the intention to conduct constant research work and continuous scientific verification and dissemination. The introduction to this context and the development of the research activity – a deliberately non-technical and/or specialised approach, connotations for which, otherwise, please refer to the following chapters – is geared towards outlining the motivations behind the thesis work, to promote and encourage reading. Following the contributions, technical considerations (see § Approfondimenti) contain more detailed analyses of the photographic and photogrammetric process and a description of the latest activities conducted, followed by a section of concluding considerations and observations on potential future developments. [edited by Author]