BIM Application for the Basilica of San Marco in Venice: Procedures and Methodologies for the Study of Complex Architectures

The BIM (Building Information Model) of the Basilica of San Marco contains the solutions to the many problems encountered during its acquisition and modelling stage. The complexity of the church and the variety of its materials (golden mosaics, capitals of different styles and origins, statues and decorations in many different marble types), the large and continuous stream of visitors, and the request for high-resolution models and orthophotos forced us to devise a strategy for the digitization process: a multiscale photogrammetric approach allowed us to acquire all materials and decorations of the basilica and, according to the use of a reference topographic network, we could split the whole work into smaller parts. Later, in the modelling stage, the decision to use a non-commercial BIM software allowed us to use NURBS (non-uniform rational B-spline) for a more accurate restitution of architectural elements and decorations and to integrate high-resolution orthophotos for the description of all surfaces (both marbles and golden mosaics). The established workflow started with the initial acquisition of images and resulted in both final models and high-quality orthophotos, so we were able to obtain different outcomes to answer the specific needs of the church, its managers, and its users

BIM SYSTEM FOR THE CONSERVATION AND PRESERVATION OF THE MOSAICS OF SAN MARCO IN VENICE

The Basilica of San Marco in Venice is a well-known masterpiece of World Heritage. It is a real multi-faceted architecture. The management of the church and its construction site is very complicated, and requires an efficient system to collect and manage different kinds of data. The BIM approach appeared to be the most suitable to collect multi-source data, to monitor activities and guarantee the well-timed operations inside the church. The purpose of this research was to build a BIM of the Basilica, considering all aspects that characterize it and that require particular care.Many problems affected the phase of the acquisition of data, and forced the team to establish a clear working pipeline that allowed the survey simultaneously, hand in hand, with all the usual activities of the church. The fundamental principle for the organization of the whole work was the subdivision of the entire complex in smaller parts, which could be managed independently, both in the acquisition and the modelling stage. This subdivision also reflects the method used for the photogrammetric acquisition. The complexity of some elements, as capitals and statues, was acquired with different Level of Detail (LoD) using various photogrammetric acquisitions: from the most general ones to describe the space, to the most detailed one 1:1 scale renderings. In this way, different LoD point clouds correspond to different areas or details.As evident, this pipeline allows to work in a more efficient way during the survey stage, but it involves more difficulties in the modelling stage. Because of the complexity of the church and the presence of sculptural elements represented by a mesh, from the beginning the problem of the amount of data was evident: it is nonsense to manage all models in a single file.The challenging aspect of the research job was the precise requirement of the Procuratoria di San Marco: to obtain the 1:1 representation of all the mosaics of the Basilica. This requirement significantly increased the effort in the acquisition stage, because it was necessary to reach a submillimetre resolution in the photographic images sufficient to distinguish perfectly each single tessera, also in the highest domes (28 meters). Furthermore, it introduced a new problem about the management of the gigapixel - orthophotos.The BIM approach presented in this paper tries to offer a solution to all these problems. The BIM application is based not on commercial software, but on a self-implemented system, which was previously tested on the Main Spire of Milano Cathedral. The multi-scale and multi-area approach have also been maintained in the BIM construction phase.In the case of Basilica di San Marco, the most important requirement was the management of the orthophotos of each single element. It was necessary to give the user the possibility to recover, for each item, not only the geometric model, but also the raster representation -orthophoto- of its surface: in order to do it, the BIM model acts as a three-dimensional catalogue

HBIM STRUCTURAL MODEL TO EVALUATE BUILDING EVOLUTION AND CONSTRUCTION HYPOTHESES: PRELIMINARY RESULTS

Historic Building Information Modelling (HBIM) is a technology that has proven to be very effective for the management, preservation, and maintenance of heritage buildings. HBIM allows a digital replica of the building, in which information can be stored, designs can be made, and future actions can be planned. To do this, it is obviously necessary to have a thorough knowledge of the building and its historical evolution. The HBIM model can therefore become the ideal place in which to develop and model construction hypotheses of building portions that no longer exist, or even record its development over time using different phases of work. Based on this context, the aim of this article is to use the HBIM approach for modelling different construction hypotheses and use the model to study the behaviour of different configurations with structural analysis. To do this, the case study of the church of San Michele Maggiore in Pavia was chosen, which in the 15th century underwent major restorations due to structural failures of the vaults of the central nave, which were replaced with the current cross vaults. In the literature there are different constructive hypotheses of the ancient vaults, which have been modelled in HBIM precisely to evaluate the different structural behaviours following the method presented. This article presents the historical analyses and geometric surveys that led to the HBIM modelling and the model itself. In the future, after careful selection of the most appropriate software, structural calculations will be made to study the structural behaviour of the building

The 2012 earthquake: An abacus of surveys & interventions in Mantua churches

After the earthquake of 2012, the ecclesiastical heritage of Mantua was so damaged to render unusable many buildings. Especially churches show a higher vulnerability in relation to their architectural features. From a recognition after the seismic event, more that 40% of the churches of Mantua were damaged with different intensity. After the first phase of expeditious damage detection, a methodical analysis has allowed to know the real state of conservation of many architectures. The Diocese of Mantua commissioned to the Mantua Campus of Politecnico di Milano the survey and digital documentation of 25 churches differently affected by the seismic event. The goal of the survey was double: a) realize the documentation necessary for the shoring and protection of damaged structures; b) prepare the drawing for the following interventions on the buildings such as restoration, reconstruction and retrofitting. Five years after the earthquake, many interventions of those identified were completed and concluded. Numerically, 129 churches were damaged and, nowadays, 115 have been restored and now they are fully open. The paper aims to illustrate the operational criteria used in the survey activity and repair operations carried out in order to identify guidelines that can direct operators in cases of new consolidation measures. All these directions were based on this premise: for historic structures, it is appropriate to accept a level of awareness with seismic risk higher than for ordinary structure, rather than act in the manner contrary to criteria of preservation of cultural heritage. In these years, we tried to identify the forms of dependence between observed damages, construction types and the conservative state before the earthquake. The goal in fact is to understand the cause of the wide loss of ecclesiastic heritage. The reason can be searched in the unfamiliarity of construction practices, techniques and materials with earthquakes or the inability of existing building to resist the seismic stress because badly maintained. These two possibilities conditioned the repair choices applied on the churches. The interventions regard different techniques which were optimized not only to be applied on buildings damaged by the earthquake but also on those that gradually show the necessity of accommodation measures. It is important, in order not to miss the operational experience gained in these years, to maximize the economic resources deployed by focusing the results achieved and verify if the followed path has been consistent and, if not, adjust the direction followed. In summary, the solutions adopted are for example: ties and anchor elements, repair works on vaults with mesh and plaster, repair works on vaults with addiction of lightweight ribs; repair works on cracked vaults with wood, steel wedges and injections of natural hydraulic lime, filling in the gaps of the masonry structure to reduce vulnerabilities

HIGH-RESOLUTION DIGITAL SURVEY OF FLOORS: A NEW PROTOTYPE FOR EFFICIENT PHOTOGRAMMETRIC ACQUISITION

High-resolution surveying of historical floors is a very common practice in both research and everyday life. The type of floors typically concerned are made of mosaic, marble and stone. Because of their intrinsic characteristics, their survey typically requires very highresolution results, to ensure excellent support for restoration, as well as in-depth knowledge of the artifact. In these cases, the focus must be kept on both geometric and radiometric content, to enable accurate metric representation and a rendering of colour and surfaces as close as possible to reality. In this research we propose a prototype of a photogrammetric acquisition system (under development) which tries to optimise the floor survey in terms of both geometric and colour documentation. In particular, the prototype makes use of the cross-polarisation technique with the aim of eliminating reflections from the images. The principle behind the prototype is the creation of a movable laboratory, a segregated space that allows excellent photographic acquisition even in difficult environmental conditions, which cannot always be controlled optimally. First tests showed its suitability and usefulness to reach the goal of a high resolution survey of historic floors

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

PHYSICAL AND VIRTUAL RECONSTRUCTION FOR AN INTEGRATED ARCHAEOLOGICAL MODEL: 3D PRINT AND MAQUETTE

Abstract. Museums perform various tasks such as collecting, cataloguing and preserving the cultural heritage (CH). In addition, they have an institutional task, which is to disseminate the heritage, discovering the most efficient tools to tell how a monument to the origin could have looked. In this process of knowledge and dissemination, digital technologies play an important role. In fact, they allow building a digital archive in which virtual copies of found objects are available to scholars for more or less in-depth analysis. Digital archives of this type also allow the dissemination of scientific data, constituting, if published, databases accessible everywhere. The role of the digital archive is also to preserve the characteristics of the finds, which are often already deteriorated, without worsening the situation through their continuous manipulation or movement. Of course, the construction of digital copies must be done in the most rigorous way so as to guarantee scholars the truthfulness of the data being analysed, and building procedures as standardized as possible to allow their use even by unskilled personnel. Moreover, museums have the very complex task of communicating the heritage, which envisages two steps: reconstruction and communication. The first phase, reconstruction, is a very complex operation, especially in the archaeological field, where there are few documents and the hypotheses are based on principles of similarity. Since no direct reference is available, the reconstruction takes place through comparison with similar objects from the same period, the same area and with the same function. Communication, then, has the task of disseminating the results and the hypotheses made, with the most appropriate tools. 3D printing allows to build three-dimensional models of reality, and therefore immediately comprehensible, even of complex forms, not always achievable with the traditional tools of modelling tools. This article describes this complex process, and its application to the funerary aediculae monument at the Museo Archeologico di Mantova, on the occasion of the refurbishment of the museum and its exhibits. In this experience, the use of new technologies is being investigated in combination with more traditional methods of representation, the maquette, but not less effective.</p

THE 2012 EARTHQUAKE: AN ABACUS OF SURVEYS AND INTERVENTIONS IN MANTUA CHURCHES

After the earthquake of 2012, the ecclesiastical heritage of Mantua was so damaged to render unusable many buildings. Especially churches show a higher vulnerability in relation to their architectural features. From a recognition after the seismic event, more that 40% of the churches of Mantua were damaged with different intensity. After the first phase of expeditious damage detection, a methodical analysis has allowed to know the real state of conservation of many architectures. The Diocese of Mantua commissioned to the Mantua Campus of Politecnico di Milano the survey and digital documentation of 25 churches differently affected by the seismic event. The goal of the survey was double: a) realize the documentation necessary for the shoring and protection of damaged structures; b) prepare the drawing for the following interventions on the buildings such as restoration, reconstruction and retrofitting. Five years after the earthquake, many interventions of those identified were completed and concluded. Numerically, 129 churches were damaged and, nowadays, 115 have been restored and now they are fully open. The paper aims to illustrate the operational criteria used in the survey activity and repair operations carried out in order to identify guidelines that can direct operators in cases of new consolidation measures. All these directions were based on this premise: for historic structures, it is appropriate to accept a level of awareness with seismic risk higher than for ordinary structure, rather than act in the manner contrary to criteria of preservation of cultural heritage. In these years, we tried to identify the forms of dependence between observed damages, construction types and the conservative state before the earthquake. The goal in fact is to understand the cause of the wide loss of ecclesiastic heritage. The reason can be searched in the unfamiliarity of construction practices, techniques and materials with earthquakes or the inability of existing building to resist the seismic stress because badly maintained. These two possibilities conditioned the repair choices applied on the churches. The interventions regard different techniques which were optimized not only to be applied on buildings damaged by the earthquake but also on those that gradually show the necessity of accommodation measures. It is important, in order not to miss the operational experience gained in these years, to maximize the economic resources deployed by focusing the results achieved and verify if the followed path has been consistent and, if not, adjust the direction followed. In summary, the solutions adopted are for example: ties and anchor elements, repair works on vaults with mesh and plaster, repair works on vaults with addiction of lightweight ribs; repair works on cracked vaults with wood, steel wedges and injections of natural hydraulic lime, filling in the gaps of the masonry structure to reduce vulnerabilities

GEOMETRIC SURVEY DATA AND HISTORICAL SOURCES INTERPRETATION FOR HBIM PROCESS: THE CASE OF MANTUA CATHEDRAL FA&Ccedil;ADE

Planned conservation approach requires a sustained, long-term action to better manage the cultural heritage assets during their life cycle. Together with programmed conservation and local interventions, there is a large amount of information related to the building; it emerges the need for an appropriate tool in which to store all data. Historic Building Information Modelling (HBIM) can be an appropriate way to address this issue. In this context, the lack of automatic tools (to speed up the project) and the need for data interpretation in the process are noticeable, especially for cultural heritage items. In this paper we present a practical case study. Starting from an integrated survey of Mantua Cathedral (located in Northern Italy) we developed a HBIM model of its fa&ccedil;ade. Particular emphasis is given to data interpretation both from geometrical survey and from historical sources. The resulting model is consistent and coherent with reality. As a result, we state that the development of a HBIM model is not an automatized process. In the process, from the survey to the final model, there is the need for a deep knowledge and a deep understanding of the building, not only in term of geometrical survey but also of its historical phases, its changes in time, its materials and the construction techniques. HBIM can be a useful instrument for planned conservation, which strongly requires a coherent model to be effective and useful. A proper model, working as an integrated archive, can increase the effectiveness of planned conservation

Applications of action CAM sensors in the archaeological Yard

In recent years, special digital cameras called "action camera" or "action cam", have become popular due to their low price, smallness, lightness, strength and capacity to make videos and photos even in extreme environment surrounding condition. Indeed, these particular cameras have been designed mainly to capture sport actions and work even in case of dirt, bumps, or underwater and at different external temperatures. High resolution of Digital single-lens reflex (DSLR) cameras are usually preferred to be employed in photogrammetric field. Indeed, beyond the sensor resolution, the combination of such cameras with fixed lens with low distortion are preferred to perform accurate 3D measurements; at the contrary, action cameras have small and wide-angle lens, with a lower performance in terms of sensor resolution, lens quality and distortions. However, by considering the characteristics of the action cameras to acquire under conditions that may result difficult for standard DSLR cameras and because of their lower price, these could be taken into consideration as a possible and interesting approach during archaeological excavation activities to document the state of the places. In this paper, the influence of lens radial distortion and chromatic aberration on this type of cameras in self-calibration mode and an evaluation of their application in the field of Cultural Heritage will be investigated and discussed. Using a suitable technique, it has been possible to improve the accuracy of the 3D model obtained by action cam images. Case studies show the quality and the utility of the use of this type of sensor in the survey of archaeological artefacts