REALITY-BASED MODELING OF MULTI-SCALE DETAILED CULTURAL HERITAGE

The aim of this contribution is to show the results of investigations held in order to provide a methodology to ease the 3d digital survey of Cultural Heritage and build reality-based models of artefacts that present peculiarities that can be detected at different scales of examination. During the last two decades, despite the improvements to documentation through digital technologies and their applications in the field of Cultural Heritage, still many Institutions are not encouraged to adopt these methodologies as a standard practice to document the heritage they are called to preserve and promote. One of the main reasons for this lack can be singled out in the high costs that are usually connected to these technologies and to the absence of standard procedures to check the quality of the acquired data that are often related to wide ranges of artefacts that present different peculiarities that it is not always possible to recollect to recurrences. In addition to these aspects, difficulties connected to the management of huge amount of data that need to be used in different contexts and for different purposes that can change through time represent a further disincentive to their widespread. The case studies presented in this paper are both archaeological finds and artworks that belong to the wide repertoire of mosaics of Ravenna that have been chosen for the multi-scale complexity of their geometry, for their small scale details and for their peculiar colour and reflectance characteristics that require particular attention during their reproduction. One of the main purposes of surveying these kinds of artefacts is to document their degradation conditions; as a matter of fact, for example, in the past, on many occasions, before restoration interventions on mosaics, specific survey campaigns allowed to collect 3d data using plaster casts in order to complete information provided by 2d pictorial representations. Within our investigations, different technologies have been compared in order to find the most suitable methodology to build reality-based models of artefacts. In particular, both range-based and image-based technologies have been tested; they highlighted different advantages and disadvantages in different contexts and for different purposes. Within our methodology, particular attention has been paid to the check of the quality of collected data and of the restored digital replicas in relationship with the main characteristics of artefacts and with communication aims. During the whole process, different versions of 3d models of the same artefacts that were acquired using different technologies have been compared. In addition, in some cases, in order to reduce redundancy of data, these models have also been compared with others derived from more detailed acquisitions using simplification procedures. The definition of the most suitable level of detail of information to be restored accordingly to the peculiar characteristics of the artefact and to the different uses was one of the main presupposes to our research. The maintenance of the required geometric complexities and of surface irregularities and meanwhile allow to manage huge amount of data, was one of the main challenges of our investigations.