Innovative uses of 3D digital technologies to assist the restoration of a fragmented terracotta statue

This paper describes how some innovative methodologies have been designed and employed to support the restoration of the Madonna of Pietranico, a terracotta statue severely damaged in the 2009 earthquake. The statue, fragmented in many pieces, has undergone a complex restoration performed by a multidisciplinary working group. The contribution of digital technologies was planned from the very beginning, since the complexity of this restoration originated the design of innovative procedures for managing the reassembly and restoration process. The Madonna test bed was therefore an example of how technology innovation could be pushed by clear application needs. A first important contribution was the study of the recombination hypothesis of the fragments. This initial phase was performed on digitized 3D models of the statue fragments, with the aim of reducing fragments manipulation, preventing further damages and increasing the capabilities to rehearse and evaluate different reassembly options. The accuracy of the 3D scanned models and the new recombination procedure introduced in this paper allowed to manage this phase in the digital domain with successful results. The digital 3D models were also used to design and produce an innovative supporting structure, constructed with a rapid prototyping device. Another important contribution concerned the study and virtual restoration of the polychrome decoration of the statue; our aim was to reproduce and restore in the virtual 3D domain the very complex original polychrome decoration, on the base of the remaining traces. Consequently, new virtual painting functionalities have been designed on the MeshLab platform (an open-source tool for 3D models visualization and manipulation) for reproducing pictorial decorations over digital 3D models and have been assessed on this specific test bed. This allowed us also to investigate the complexity of the virtual repainting process and to identify further technology enhancements. Finally, computer graphics technologies have been also used to produce a video that tells the story of the restoration.     

Documentation of cultural heritage using digital photogrammetry and laser scanning

Precise documentation of cultural heritage status is essential for its protection and scientific studies carried out during the restoration and renovation process. The close range photogrammetry has been used successfully for documentation of cultural heritage. With recent developments in computer and information technologies, this well-known traditional method has been replaced with digital close-range photogrammetry. This new method offers us new opportunities such as automatic orientation and measurement procedures, generation of 3D vector data, digital ortho-image and digital surface model. Terrestrial laser scanning is another technology that in recent years has become increasingly popular for documentation which provides very dense 3D points on an object surface with high accuracy. In addition, the 3D model and digital ortho-image can be easily generated using generated 3D point cloud and recorded digital images.     

Three-dimensional modelling of statues: the Minerva of Arezzo

The Minerva of Arezzo is an ancient bronze statue located at the Museo Archeologico in Florence and currently under repair at the Restoration Centre of the Soprintendenza Archeologica of the Tuscany Region. We assembled a complete three-dimensional (3D) digital model of the Minerva before the restoration started. More 3D models will be produced to keep track of the variations that occurred during the restoration process, up to the final acquisition of the form of the restored artwork. The modelling of the Minerva will be the focal point of an ambitious “Minerva Project” that involves the integration of data from other sources in a 3D digital model of the object. Besides this, the project is aimed at showing how 3D techniques can be used to design useful and easily manageable new tools for the diagnostics of archaeological objects. 3D measurements have been realized by means of a high-resolution laser scanner developed at National Institute for Applied Optics (INOA). The instrument is composed of commercial low-cost components in order to be competitive with the very expensive commercial devices. Besides this, our scanner is supported by an efficient and flexible software developed by Consiglio Nazionale delle Ricerche (CNR) that supports all the post-processing phases of a 3D scanning session (range data alignment, merge and simplification).     

Digital preservation of Brazilian indigenous artworks: Generating high quality textures for 3D models

Three-dimensional (3D) digital preservation aims at generating 3D models of objects that have cultural or scientific value. It allows realistic visualization of objects through virtual museums or scientific applications, and the restoration of the preserved object in case of natural wear or accidents. This work contributes to this research area by presenting a method to improve color texture quality of 3D models obtained from color and depth images of a laser scanner. Although this device offers precise depth information, the resulting color information is still poor and limits the generation of realistic textures. Our approach is to capture photographs of the object with a high-resolution digital camera and use them to generate a new color texture for the 3D model. Our work proposes a practical technique, easy to replicate, to generate high quality textures for 3D models from photographs. The method is composed by three main steps: (1) calibration of the image acquisition devices; (2) data acquisition; and (3) texture generation. In this paper, we detail our color texture generation method and apply it on the digital preservation of many artworks made by native Brazilians (indians) from the Wauja and Karaja communities. These indigenous communities are acknowledged as great ceramic artists, each bearing their own main themes, using a very rich symbolism in their paintings. Their artworks represent important aspects of the native South American culture and their digital preservation is motivated by three main reasons: (1) their fragility; (2) the paintings loose their original appearance with time; and (3) the possibility of extinction of these communities. We present several results of preserved artworks with enhanced quality realistic texture maps. Also, we present a methodology to analyze the quality and accuracy of texture maps. The resulting 3D models can be visualized through a tool we developed to support the virtual exhibit of 3D preserved heritage.     

The Basilica of San Vitale in Ravenna: Investigation on the current structural faults and their mid-term evolution

A finite element model was developed to analyze the Basilica of San Vitale in Ravenna (Italy), a Byzantine building which suffers diffused cracking and excessive deformation, mainly as a consequence of complex architectural vicissitudes (extensions, demolitions …) and ground settlements. In the structural analyses, account was taken of permanent loads (self-weight), boundary displacements increasing in time, and seasonal thermal changes. Thanks to previous topographical surveys of part of the building, to chemical and mechanical investigations, the geometry of the Basilica and the main physical properties of the materials are reasonably well defined. The geometric model does not virtually neglect any structural element and accounts for the lack of symmetries in the building. Because of the complexity of the geometric model, a simplified (linearly elastic, isotropic) constitutive law had to be assumed to keep the computing time within reasonable limits. Accordingly, the performed analyses constitute only a first step toward the understanding of the structural behavior of the Basilica, as the adopted constitutive law can only partially explain the surveyed crack pattern, which is influenced by the brittleness and the anisotropy of the constituent materials.     

An integrated and automated segmentation approach to deteriorated regions recognition on 3D reality-based models of cultural heritage artifacts

In the field of Cultural Heritage, image analysis represents an indispensable practice for restorers to collect information about the state of preservation of monuments and artifacts and plan restoration interventions. In addition, during the last two decades, the wide spread of remote sensing technologies and the possibility to build 3D reality-based models of artifacts allow the extension of image analysis to 3D environments. In this context, the purpose of this contribution is to show the results of investigations held in order to provide a methodology for the automatic detection of deteriorated areas within architectures and artifacts using colour images as a field of examination. Using both 2D and 3D segmentation approaches, our methodology aims at speeding and efficiently performing the automatic detection of deteriorated zones within Cultural Heritage and therefore segment 3D digital models acquired using different survey technologies. Within our investigations, we selected case studies concerning recurrent deteriorations, such as, for example, detachments, cracks and chromatic alterations; we run them both to manual and to automatic recognition and selection tests, in order to compare the results obtained using these approaches and evaluate the reliability of the automatic one. Results comparison included computational and user time, quantification of the deteriorated area error between manual and automatically detected zones. Additional parameters characterizing the specific type of deteriorations were also computed for each case study. Comparison between the automatic and the manual procedure showed that the automatic detection is faster and reliable in all our selected case studies, with evident improvements in the efficient evaluation of the entity and extension of deteriorated areas on 3D geometry.     

Automatic registration of large range datasets with spin-images

Terrestrial laser scanning technique has represented one of the more advances occurred in the last years in the field of data acquisition. Time-of-Flight (TOF) systems provide a fast and reliable tool to measure millions of 3D points allowing a very effective and dense measurement of the surface geometry. Nowadays, the generation of high quality 3D models is a practice applied to different kind of objects: small or medium size artworks, parts of human body, cars, buildings, civil infrastructures (like dams, bridges, plants, etc.) and whole archaeological sites as well. In most cases, in order to capture the whole object geometry a number of single scans need to be acquired from different positions and then stitched together (i.e. registered each other) to generate the full 3D model. The automatization of the registration of multiple scans acquired from a terrestrial laser scanner (TLS) still represents a very attractive research field. The chance to automatically align several point clouds would reduce processing costs in terms of time and human resources. In addition it would allow even non-specialist users to produce 3D models with good quality. This paper contributes to this research area by presenting a method for the automatic registration of very dense point clouds acquired by TLS systems. The proposed solution is an extension to large datasets of an automatic range data registration procedure we developed a few years ago for the modelling of point clouds acquired with close-range laser scanners. Such procedure, based on the spin-images (SIs) algorithm, has been then improved with the introduction of a multi-resolution method that generates a pyramid of spin-images in order to speed up the matching between adjacent scans. The results we present show that this method can be successfully applied for the automatic registration of high density laser scans of complex and large structures of Cultural Heritage.     

Principal Component Analysis in monument conservation: Three application examples

Multivariate statistics is a well-known and invaluable tool in archaeological science but its use is limited in monument restoration. The aim of this work is to demonstrate the effectiveness of Principal Component Analysis (PCA) on the characterization, technology and weathering condition investigation of building materials from historical monuments.Towards this aim, three examples are given:The first one is a provenance and technology investigation of the Aghia Sophia (Istanbul, Turkey) bricks, some of which had to be replaced due to weathering, during recent restoration works. It was proved by PCA that the original clay, used for the construction of the bricks, is not similar to the clay of other contemporary constructions in Istanbul but presents high similarity to the raw material of the bricks from a contemporary church in the island of Rhodes (Dodecanese, Greece). Additionally, the technology of the bricks was studied by mercury intrusion porosimetry, strength tests and Scanning Electron Microscopy. The use of PCA gives a very comprehensive way to present the difference in the technology of the dome bricks.The second presents a classification of mortars from medieval (Byzantine) monasteries, based on their microstructural characteristics (porosity, reverse hydraulicity ratio) and strength measurements. The PCA grouping gives an illustrative diagram depicting the correlation between mortar syntheses and resulting characteristics.The third case shows an example of the correlation between environmental pollution data and data from the weathering layers of marble surfaces (patina composition, orientation of the monument surface, etc.).     

Daily natural heat convection in a historical hall

The use of numerical simulation methods for the Cultural Heritage is of increasing importance for the analysis, conservation, restoration and appreciation of works of art. This is particularly important when their preservation and planned maintenance is the primary aim. Today museums, and particularly historical buildings converted to museums, should be considered as places where precious artefacts should have first-rate protection and conservation. It is a question of solving the compromise between protection, conservation and comfort for works of art and/or visitors, with the consequence that preservation and planned maintenance criteria must prevail over use requirements. Refurbishment and conservation of a building, and requirements for visitor presence and works of art need different thermo-physical indoor parameter values. The present paper concerns the thermal and air velocity analysis of the Salone dei Duecento (the Hall of the Two Hundred of the Palazzo Vecchio (Old Palace)) in Florence. In this paper an appropriate transient 3D model by Computational Fluid Dynamics (CFD) software based on the finite element method (FEM) was used. Variations and interaction between indoor and outdoor microclimatic conditions, and thermo-physical behaviour of the building connected to lighting, visitor presence and cooling–heating fan coils system were considered. The 3D modelling method provided by the present paper can be applied to several situations where there is interaction between outdoor and indoor climate variations and the building structure. It can be very useful for defining measures to preserve tapestries, understanding deterioration processes, and developing new conservation techniques and strategies for care and exhibition.     

3D reconstruction of small sized objects from a sequence of multi-focused images

3D reconstructions of small objects are more and more frequently employed in several disciplines such as medicine, archaeology, restoration of cultural heritage, forensics, etc. The capability of performing accurate analyses directly on a three-dimensional surface allows for a significant improvement in the accuracy of the measurements, which are otherwise performed on 2D images acquired through a microscope. In this work we present a new methodology for the 3D reconstruction of small sized objects based on a multi-view passive stereo technique applied on a sequence of macro images. The resolving power of macro lenses makes them ideal for photogrammetric applications, but the very small depth of field is their biggest limit. Our approach solves this issue by using an image fusion algorithm to extend the depth of field of the images used in the photogrammetric process. The paper aims to overcome the problems related to the use of macro lenses in photogrammetry, showing how it is possible to retrieve the camera calibration parameters of the sharp images by using an open source Structure from Motion software. Our approach has been tested on two case studies, on objects with a bounding box diagonal ranging from 13.5 mm to 41 mm. The accuracy analysis, performed on certified gauge blocks, demonstrates that the experimental setup returns a 3D model with an accuracy that can reach the 0.05% of the bounding box diagonal.     

Dynamic identification of historic masonry towers through an expeditious and no-contact approach: Application to the “Torre del Mangia” in Siena (Italy)

The paper presents a synergic and multidisciplinary approach where laser scanner survey, radar interferometric monitoring and finite element (FE) numerical modelling are used for expeditious and no-contact dynamic identification of monumental masonry towers. The methodology is applied to a real case of great historical interest: the “Torre del Mangia” (Mangia's tower) in Siena (Italy). The tower geometry was acquired through Terrestrial Laser Scanning (TLS) techniques. The tower oscillations were detected using an interferometric radar in “Piazza del Campo”, the square facing the Mangia's Tower, along three alignments, and movement of the structure at several heights were recorded. A FE model, built on the basis of the geometry acquired through the TLS, was used to interpret and verify the physical meaning of the experimental results. Through the discussion of the case study, the paper shows that the proposed approach can be considered as an effective and expeditious method for assessing the dynamic behavior of monumental buildings (and to plan interventions) on territorial scale.     

The moral economy of face: marketized gift and depoliticized solidarity in South Korea’s fair trade

ABSTRACT

Metaphors of ‘face’ are often found in South Korea’s fair trade activism, as fair trade is frequently described as ‘face-to-face commerce’ and its goal is presented as pursuing ‘global trade with a human face.’ By asking how and why fair trade relies on the metaphors of face, this article analyzes the political implications and limits of the trope. I first examine the intimate connection between gift-exchange and face based on Marcel Mauss’s analysis of the gift and I present face as a locus of symbolic recognition and politics. Next, drawing on ethnographic research into Beautiful Coffee, the largest fair trade organization in South Korea, I illuminate fair trade as a hybrid practice of ‘marketized gift-exchange’ in which the various faces of producers and consumers are produced and circulated along with market transactions. In examining the meanings of those faces, I maintain that the prevalent metaphor of face in fair trade betrays the contradictory nature of market-based solidarity that is sought through the activism to redefine the whole economic structure based on moral and ethical practices.     

Assessment of synthetic polymeric coatings for the protection and preservation of stone monuments

The performance of five synthetic coatings for the protection of stone monuments of Hellenistic and Byzantine period has been evaluated. The selected coatings included four commercially available siloxane-, siloxane/acrylic- and perfluoroether-based compositions, as well as a new composition based on newly synthesized fluoro-organosilane. The coatings were applied onto petrologically different stone substrates, such as marble, travertine, sandstone and a newly baked brick compatible with Roman period bricks, used for the restoration processes in Galerius Palace, Thessaloniki, Greece. The coatings' protective efficiency was investigated by measurement of water–stone contact angles, water vapor permeability, and water absorption by capillarity. The optical properties of the applied coatings were also investigated and they were also ranked with regard to their optical characteristics.     

Importance of digital close-range photogrammetry in documentation of cultural heritage

It is an indisputable reality that the most important thing for transmitting cultural heritage to posterity is a sensitive documentation. Up to the present there have been many developments in documentation of cultural heritage by developing technology, and contemporary documentation techniques have progressed speedily. In time, modern methods have become preferable to conventional methods in architecture generally in the existent state and in determination of deformations and preparation of measured drawing projects of historical edifices. Digital and 3D data, rich visual images obtained by digital close-range photogrammetry, and orthophoto images of edifices, are governed and shepherded in documentation and future conservation projects. Also, these methods supply much ease, precision and time-saving in measured drawing projects when compared with conventional methods. In this study, contributions of digital close-range photogrammetry to measured drawing projects were evaluated. A historical building, which had been exposed to fire two times in Konya (Turkey), was photographed and its situation before and after the fire was demonstrated. In addition, the building's measured drawings of facade and its 3D model were completed using digital close-range photogrammetry. The building's present status and its reconstruction project is indicated and how digital close-range photogrammetry contributes to measured drawing, reconstruction and restoration projects is presented. Furthermore, the significance of present-day use of digital close-range photogrammetry in the acquisition of data and preparation of measured drawing projects for historical buildings is emphasized. This study has been completed by photogrammetrists, architects, urban planners and restorers.     

A flexible approach to reassembling thin artifacts of unknown geometry

We present a novel 3D reassembly method for fragmented, thin objects with unknown geometry. Unlike past methods, we do not make any restrictive assumptions about the overall shape of the object, or its painted texture. Our key observation is that regardless of the object's shape, matching fragments will have similar geometry and photometry along and across their adjoining regions. We begin by encoding the scale variability of each fragment's boundary contour in a multichannel, 2D image representation. Using this multichannel boundary contour representation, we identify matching sub-contours via 2D partial image registration. We then align the fragments by minimizing the distance between their adjoining regions while simultaneously ensuring geometric continuity across them. The configuration of the fragments as they are incrementally matched and aligned form a graph structure that we use to improve subsequent matches. By detecting cycles in this graph, we identify subsets of fragments with interdependent alignments. We then minimize the error within the subsets to achieve a globally optimal alignment. We leverage user feedback to cull the otherwise exponential search space; after each new match is found and aligned, it is presented to a user for confirmation or rejection. Using ceramic pottery as the driving example, we demonstrate the accuracy and efficiency of our method on six real-world datasets.     

Reconstruction of photorealistic 3D model of ceramic artefacts for interactive virtual exhibition

To create photorealistic three-dimensional (3D) models of real scenes and objects is a challenging problem that demands advanced knowledge of computer vision and computer graphics. Systems that can reconstruct the 3D model of cultural artefacts have found many applications such as virtual museum and historical archiving. While there are methods for 3D digitization of cultural artefacts with high geometric resolution, there are still limitations in achieving high textural resolution for virtual exhibition. One major problem is that the object surface exhibits specular reflection of illuminated light during the acquisition of surface texture. The shading of the target object does not match to other objects or pictures in the virtual scene. Also, if texture of the object must be composed of multiple images, the mismatch of shading (radiometric difference) among the images can be very prominent. In order to create high visual quality exhibition, the specular reflections must be eliminated and then the virtual scene is relit by a synthetic light source. Most existing methods for the identification and removal of specular reflection component demand special device or rely on information obtained in a single image. In order to reconstruct a complete 3D model, we need to acquire a multi-view image sequence. We therefore propose a new method that is applicable for the separation of diffuse and specular reflection components in multi-view image sequence. Also, our method can tackle the specular reflection across the texture boundary. The image sequence is first normalized by the estimated illumination color. Based on the dichromatic reflection model, the specular chromaticity is replaced by the corresponding diffuse chromaticity, which can always be found in neighboring views with the highlights already faded away. We test the new method in modeling Yixing ceramic teapots. The shape model of the teapot is obtained by a laser scanner. The diffuse image sequence is then used to generate the texture map. We create the virtual scene with the photorealistic 3D teapot model, some synthetic 3D models and still pictures. Interactive exhibition of the artefact is achieved with the control of the mouse and simple keyboard commands. This paper gives an account of the procedures for the creation of interactive virtual exhibition of ceramic artefacts.     

The importance of quality: How music festivals achieved commercial success

This paper examines the characteristics that are important to current commercially viable massive music festivals when making decisions on who to hire while facing horizontal and vertical quality differentiation with heterogeneous preferences among intended consumers. A model of customer demand motivates the empirical analysis using a unique bundling problem in which the consumer faces an unknown element, depending on festival reputation for expected utility. The empirical analysis utilizes characteristics important to the negotiation between the festival and the band as input. Musical acts with an album recognized as being of a high quality are about 33 % more likely to be hired by a festival in the year of release and 50 % more likely the following year. A top touring band is 40 % more likely to be hired in the first year, but 45 % less likely to be hired in the following year, likely due to an increased cost of hiring. Festivals hire quality, unknown bands to take advantage of the lower costs of lesser known acts by leveraging a reputation for evaluating quality before the consumer. Other industries face similar input decisions, giving the results a broader application.     

3D preserving xviii century barroque masterpiece: Challenges and results on the digital preservation of Aleijadinho's sculpture of the Prophet Joel

We present our recent efforts in the digital preservation of a set of baroque sculptures made by Antônio Francisco Lisboa, known as O. Aleijadinho, which is an important American baroque artist. The set was made in the beginning of the xix century and is composed of 12 near real sized sculptures, hand-carved in soapstone. These sculptures represent 12 of the 16 prophets from the Holy Bible and are part of a UNESCO World Heritage Site. Our group has been collaborating with UNESCO in a project that aims to preserve all these statues. We hereby present our initial efforts, consisting of the 3D digital preservation of the Prophet Joel sculpture. We developed a complete 3D digital preservation pipeline composed of four main stages: data acquisition, 3D reconstruction, texture generation and 3D model visualization. By evaluating our results in this first sculpture, we discuss the improvements we conceived before applying our pipeline in the remaining ones. Finally, we present the 3D model of the Prophet which registers the sculpture's current state and will be used in restoration, research and educational activities. We believe this contribution may be useful to guide further research on similar scenarios, showing how to avoid some practical mistakes and achieve good results.     

Methods and tools for the classification and cataloging of antique moulds from the collection of the Richard-Ginori factory

This study proposes a procedure for digitally classifying and cataloging moulds which belong to the historic collection of the Ginori porcelain factory in Doccia (Sesto Fiorentino, Italy). In addition to a vast number of antique plaster moulds, this collection includes artistic porcelain artifacts obtained from casting porcelain using the moulds and models made of various materials. The proposed methodology includes two workflows: the first starts with photographic and casting processes conducted recently on various groups of moulds and involves historical surveys for investigating the relationships between the various sets of moulds, the models from which they were derived and the porcelain objects derived from them. The second workflow was applied when no information was available for a set of moulds, and involved 3D scanning of the moulds, with virtual reconstruction of the corresponding model followed by a final art historical survey like that used in the first procedure. 3D scanning techniques and successive model reconstruction can also be applied for obtaining a virtual model in the first process, when the physical model was lost, damaged or never existed. The variety and extent of the Ginori collection suggested the use of a customized Data-Base (DB) and a set of functions designed to manage and extract information, data and archived images. This filing system, called DocciaDigitalArchive (DDA), also makes it possible to specify the relationships between the different typology samples (prototype models, moulds derived from them, handmade porcelain objects produced from these moulds), which are associated when the same subject is portrayed. The DB structure conceived also provides the possibility of incorporating pictures and data of known archetypes. This additional information makes it possible to place each subject in its historical and artistic context. For each sample filed in the DDA system, documentary cards, which summarize data, images, reports and links to other entities or samples connected to the subject consulted, can be viewed on a suitable interface.     

Using 3D digital models for the virtual restoration of polychrome in interesting cultural sites

In most cases, the polychrome paintings that decorated heritage buildings no longer exist or are reduced to mere remnants. These facts decontextualize the sites in their historical and artistic evolution, distort the intention under which they were conceived, and hamper their accomplishment. Current recovery methods are restricted to the stabilization of the remains in their present status, requiring a lot of completely manual work that is expensive and almost unrelated to the use of new technologies. Three-dimensional digitalization and modelling is proved to be the basis for the virtual recovery of paintings in a significant edifice. To do so, an innovative methodology is presented that allows the 3D geometric information of a site (captured using a laser scanner) to be combined with specially designed 2D artistic images. The resulting 3D digital models can then be focused, with high efficiency projectors, on the equivalent area of the original site, and also used as raw material to compose a video-projection without perspective effects to emulate, with due rigour, the primitive appearance, its evolution along time, the effects of the deterioration, or other interesting aspects. The results obtained at Sta. María de Mave (Palencia, Spain) are presented, supporting the potential of this new methodology not only as a scientific way to discuss possible restoration hypotheses with experts or as a didactic tool for narrating the historical evolution of a monument, but also as a spectacular show for tourists.