MODELLING AND ACCURACY IN A BIM ENVIRONMENT FOR PLANNED CONSERVATION: THE APARTMENT OF TROIA OF GIULIO ROMANO

Modeling of Cultural Heritage in a BIM environment, and in general of existing buildings, requires special attention because there are two diametrically opposed possibilities. On the one hand the attempt is to realize a very complex and accurate model, in order to provide the most comprehensive representation of the architecture as possible. The opposite position leads to build a very schematic and symbolic model of as-built architecture. It is not easy to determine which is the right balance between these two attitudes because each architecture requires a personalized approach and not standards. It’s, however, necessary to find rules to figure out which items are represented, what is the minimum level of detail to consider adequate and how to deal with alterations from simple and linear geometries. These two facing possibilities deal with different goals and tools. In the field of restoration or planned conservation, that is the most common approach for existing buildings, the attention focuses on the exceptions and particularities of each architecture: the important aspect is to understand and describe exactly each part as a singularity (as it is). In this context it is very difficult to find a standard or a common solution. The first possibility of modelling seems to be very close to this approach, but it clashes with two important aspects. A first problem concerns the modelling software. Usually commercial BIM modelling software doesn’t allow to realize very complex and high detailed solutions. They prefer working with predefined families and try to categorize each element in standard solution. The possibility to build new families is expected, but it often requires a lot of time. The second difficulty is the real efficiency of such an accurate model. In fact, it could be very difficult to link external elements to the model or use it in many traditional BIM applications. In this paper, we suggest another possible approach that represents the first result of a research about the modelling of Cultural Heritage for BIM application. The proposed solution aims to give as much information as possible about the architecture, and, at the same time, to guarantee a higher efficiency. In this case we considered commercial BIM software like Revit or Archicad. They are the most widespread and well-known software BIM oriented and they also allow the use of their embedded database structure. The core of our solution is to describe the architecture not only by a 3D model but also by the representation of the reliability of the accuracy of the model itself. In this way we try to combine the necessity of working with commercial software, in which it is difficult to be very accurate, and the information about the real object. In historical complex architecture, for example, it is very difficult to find a straight and planar wall. It is quite difficult, or at least time consuming, to model that kind of wall with high accuracy. But it is possible to represent the real wall by a schematic wall with a false color map which describes where the 3D model is well fitting and where there are some differences. In this way we don’t lose any information but, at the same time, we have a very usable BIM model

Survey and modelling for the bim of Basilica of San Marco in Venice

The Basilica of San Marco is a singular case in the field of Cultural heritage, as it constitutes a construction site always active for the maintenance and preservation of the basilica itself. The continuous intervention of conservation, due to the particular environmental conditions of Venice and the opening to the public, together with the complexity of the building itself, imposes the need to identify an optimized management system. For this reason, in 2013 the Procurator of St. Marco Basilica commissioned the construction of a 3D model of the Basilica to be used for the creation of a BIM. The model must meet the required precision of the scale of 1: 50, and should also include, in addition to the geometric description, a description of the mosaic and marble surfaces of the basilica through high resolution orthophoto which are essential for the restoration of the mosaics. The complexity of the church and the large and continuous flow of public led to work in non-optimal conditions especially for the acquisition stage. The basilica has certain peculiarities that led to some important choices, for example the use of photogrammetry instead of laser scanning technique. The same technique was preferred also by the need to realize, in addition to the geometric model, high-resolution orthophotos of marbles and mosaic surfaces. The modelling of the basilica has highlighted a number of problems related to the building features. The basilica, indeed, is the result of the juxtaposition of elements (capitals, columns) with different origin, which therefore cannot be standardized in special libraries. Moreover, especially in the extensive mosaic areas, there are not edges that characterize the architecture, but only beveled surfaces. This has resulted in a change also in the modeling paradigm with the need to identify alternative systems even for the construction of simple elements. Therefore, we decided to model using NURBS since it is the method that allows greater adherence to reality and, at the same time, a model with acceptable dimensions in terms of navigation and usability. Only the most sculptural pieces such as capitals and statues have been replaced by mesh models. As we were interested in different elaborations, the results of this work are a geometric NURBS model for the subsequent insertion into BIM environment, with the possibility of extracting two-dimensional drawings such as plans and sections, a mesh model with low resolution textures for online navigation and high resolution orthophotos. The survey work and modeling has been almost completed for the interior of the basilica whereas only the external remains to be acquired and modeled. For the management of the entire work it was decided to use the data organization system already used by the Politecnico di Milano for the Duomo di Milano. The BIM3DSURVEY system will be essential not only to manage the finished model, but it has been very useful also during the construction phase because it allows us to divide the entire work into more work units. However, this system required some changes to meet the peculiarity of this BIM, in particular the need to append and link the orthophotos to real surfaces, in order to use the model also as a spatial index for the images

Conoscenza e gestione del patrimonio costruito storico. Le nuove frontiere del B.I.M.

The BIM Modeling of Cultural Heritage requires special attention, dealing with at least two completely different aspects. On the one hand, the problem concerns the elaboration of a complex and accurate model in order to provide the most complete representation of a building; on the other hand, modeling leads to a very schematic representation of a built architecture. It is not easy to define the right balance between these two attitudes, since each building requires a tailored and not a standard approach. Therefore, it is necessary to define rules to figure out which items are to be represented and which is the minimum detail level. With regard to restoration, the attention focuses on singularity and particularities of each existing architecture: it is meaningful to realize and describe accurately each part as a distinctive issue. The first above-mentioned possibility of modelling seems to be very close to this approach, but it clashes with two important aspects. The first problem concerns commercial modelling software that prefers working with predefined “families”. Though it is possible to build new families, it oftenrequires a lot of time. The second problem is the actual adaptability of such an accurate model: in fact, it could be very difficult to link external elements to the model or use it in most of traditional BIM applications. In this paper, we suggest a different possible approach. The proposed solution aims to give as much information as possible about the building, and, at the same time, to achieve a higher efficiency. In this way no information are lost and, at the same time, a very usable BIM model can be achieved