FEDERATED HBIM MODELS FOR CULTURAL HERITAGE: SURVEY MODEL AND CONCEPTUAL MODEL

The federation of models is a pillar of the BIM (Building Information Modelling) approach: it allows to keep the contents of each discipline separate during the modelling-creation phase, and to merge them together later during the project management phase, from its feasibility to the construction site, to the management of the entire life-cycle of the building.Generally, these models refer to specific disciplines and the architectural, plant and structural model are always identified.When the asset belongs to Cultural Heritage, more generically an existing building, the BIM approach (at this point HBIM - Historic Building Information Modelling) is faced with an additional level of complexity since it is necessary to model something existing (the building in fact) and of which not much information is known. The geometric complexity of the asset often aggravates this situation because if the parametric modelling is preferred, it is difficult to represent such irregular morphologies, and if the surface modelling and a more geometrical detail is preferred, the model becomes very heavy.In many cases the choice is to approximate reality as best as possible through specific and tailor-made modelling approaches, often complex and with some borderline methods, if compared to BIM logic. In other cases, however, it makes sense to define when the geometric complexity and the reliability of the model are necessary, and when, instead, a simplification is required in order to effectively manage the information.The case study presented in this paper is the Arch of Augustus, in Aosta, for the HBIM approach it has been chosen to separate the two approaches,placing side by side the federated models referred to the classical disciplines with two models of the current state: one very accurate with the purpose of maintaining all the quality of acquired 3D geometric information, while the other absolutely schematic, necessary as a 3D index for the information.The approach described here, however, requires a preliminary reflection in order to define the BIM granularity - the smallest object in the model - and to define the methodological procedures that allow the bidirectional relationship between survey model and conceptual model. This paper provides insigth oif the importance of the relation between survey model and conseptual model. Future works will try to make this relation more stronger and efficient.