GCH 2020 - Eurographics Workshop on Graphics and Cultural Heritage

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Another Brick in the Wall: Improving the Assisted Semantic Segmentation of Masonry Walls
(The Eurographics Association, 2020) Pavoni, Gaia; Giuliani, Francesca; Falco, Anna De; Corsini, Massimiliano; Ponchio, Federico; Callieri, Marco; Cignoni, Paolo; Spagnuolo, Michela and Melero, Francisco Javier
In Architectural Heritage, the masonry's interpretation is an essential instrument for analyzing the construction phases, the assessment of structural properties, and the monitoring of its state of conservation. This work is generally carried out by specialists that, based on visual observation and their knowledge, manually annotate ortho-images of the masonry generated by photogrammetric surveys. This results in vectorial thematic maps segmented according to their construction technique (isolating areas of homogeneous materials/structure/texture) or state of conservation, including degradation areas and damaged parts. This time-consuming manual work, often done with tools that have not been designed for this purpose, represents a bottleneck in the documentation and management workflow and is a severely limiting factor in monitoring large-scale monuments (e.g.city walls). This paper explores the potential of AI-based solutions to improve the efficiency of masonry annotation in Architectural Heritage. This experimentation aims at providing interactive tools that support and empower the current workflow, benefiting from specialists' expertise.
Ernst Grube: A Contemporary Witness and His Memories Preserved with Volumetric Video
(The Eurographics Association, 2020) Worchel, Markus; Zepp, Marcus; Hu, Weiwen; Schreer, Oliver; Feldmann, Ingo; Eisert, Peter; Spagnuolo, Michela and Melero, Francisco Javier
''Ernst Grube - The Legacy'' is an immersive Virtual Reality documentary about the life of Ernst Grube, one of the last German Holocaust survivors. From interviews conducted inside a volumetric capture studio, dynamic full-body reconstructions of both, the contemporary witness and its interviewer, are recovered. The documentary places them in virtual recreations of historical sites and viewers experience the interviews with unconstrained motion. As a step towards the documentary's production, prior work presents reconstruction results for one interview. However, the quality is unsatisfying and does not meet the requirements of the historical context. In this paper, we take the next step and revise the used volumetric reconstruction pipeline. We show that our improvements to depth estimation and a new depth map fusion method lead to a more robust reconstruction process and that our revised pipeline produces high-quality volumetric assets. By integrating one of our assets into a virtual scene, we provide a first impression of the documentary's look and the convincing appearance of protagonists in the virtual environment.
A NLP Enhanced Visual Analytics Tool for Archives Metadata
(The Eurographics Association, 2020) Ozdemir, Anil; Müstecep, Dilara; Agaoglu, Orhan; Balcisoy, Selim; Spagnuolo, Michela and Melero, Francisco Javier
Today, almost all cultural heritage (CH) institutions are starting to digitize parts of their collections and archives to improve accessibility, preservation of originals, publicity, and visibility of the institution on the Internet. With this recent development, digital document collections have been multiplying. These collections are spread over more than one area of life in a vast domain, including art, history, mathematics, physics, etc. Such a situation creates a substantial volume of documents digitally available. Also, it creates the need for various approaches that allow users to understand latent meanings in collections, discover and investigate relationships, and extract the necessary information from collections. To address this need, we introduce a visual exploratory tool that facilitates the uncovering of hidden information and stories underlying documents, extracting the key individuals, temporal expressions, locations, entities, and keywords within the documents ,establishing a network between documents and allow researchers and archivists to form and test hypotheses and observe individual relationships, networks, and stories present in the archives metadata collections.Consequently, we have designed and developed a visual exploration tool for large archives with limited metadata employing state of the art Natural Language Processing (NLP) techniques to assist cultural heritage researchers. To design such a tool, we have collaborated with archive professionals from an cultural institution, SALT (https:// saltonline.org/) which focused on public service producing research-based exhibitions, publications, and digitization projects. As a result of our conversations Salt team we decided to use Waqfs of Crete which is an archive consisting of official records of Muslim inhabitants of Crete. Documents spanning the period from 1825 to 1928 in Ottoman Turkish and Greek provide an opportunity to examine the multi-layered social structure on the island, especially from a cultural and economic perspective. The metadata contains information for approximately 10 thousand documents and includes the summary of those documents, the year they were published, the location, the language used, and the documents' picture. Also, We extracted various features including locations, key individuals, dates, entities and keywords from the document summaries on metadata using NLP methods including regular expressions for extracting , and word embedding models for capturing similarities between documents. We have integrated all of these features into designed tool to let the user to see networks that can represent the relationship between documents, as well as easily access similar documents in the archive. In the network we demonstrated, particular nodes correspond to the documents itself. To assign an weighted edge between two documents in the network, the total number of shared individuals and keywords between documents are computed and edges are set based on a predetermined threshold value. This threshold has been found by manually tweaking both considering the speed at which the result is reflected on the application and average number of shared attributes. To capture similarity between documents, we used state-of-theart word embedding models including Word2vec, FastText and Transformer which provides a method to compute dense vector representations for documents. Consequently, each document was represented as fixed-sized mathematical vectors as output of each model, and the similarity between documents was calculated by taking the arithmetic cosine similarities of vectors. The designed interface consisting of six components which includes interactive map that allows the user to view documents in different locations and view the document networks that formed by calculating total number of shared attributes between documents. Remaining components include information box that contains document-specific attributes such as location, time, person, entities, and keyword, document browser that enable users and researchers to browse documents easily, individual and keyword search menu and filtering panel. In this way, the users may find documents that are roughly related to each other very quickly. Later, the user can browse each document on its network and view documents that have common individuals and keywords with each other. Thus, the user may follow the interactions between documents like a story and able to do this for all the people who lived in the 19th century on Crete's island.
Possibilities and Challenges of Portraying Cultural Heritage Artefacts using Augmented Reality: the Mjällby Crucifix Case Study
(The Eurographics Association, 2020) Garro, Valeria; Sundstedt, Veronica; Putta, Advaith; Sandahl, Christoffer; Spagnuolo, Michela and Melero, Francisco Javier
The increasing application of immersive technologies, i.e. virtual reality (VR) and augmented reality (AR), in cultural heritage (CH) offers new ways of displaying artefacts and historical sites. VR and AR provide an added value to the visitor experience from several different aspects, e.g. interactivity or sense of presence. VR and AR technologies open the possibility for the visitor to visit reconstructions of historical sites and observe 3D replicas of CH artefacts. Moreover, these technologies, especially AR, can bring some artefacts back to their historical locations adding a new dimension to the visitor experience. We present an ongoing case study exploring the use of AR in the portrayal of a CH artefact, namely the Mjällby Crucifix in the Blekinge Museum, located in Southern Sweden. This crucifix is a medieval artefact which was originally placed in the Mjällby church and is currently preserved at the Blekinge Museum warehouse. The artefact is displayed lying in horizontal position on a low stage surrounded by other artefacts. Due to its large size (310 cm high and 260 cm wide) and its current position, it is not possible for the visitor to have a close view of the artefact. We plan to display a 3D replica of the artefact via an AR application using a hand-held device. The digital replica can be visualised in its original vertical position both in a chosen location in the museum and in the Mjällby church enhancing the visitor experience. A prototype of the AR application has been developed and showcased to a group of experts from the Blekinge Museum. The digitisation of the crucifix artefact has been done using an Artec Leo 3D scanner which captures both geometry and texture information. We developed a marker-based AR prototype application which runs on Android mobile devices supporting Google AR platform ARCore. We used a picture of the original crucifix as a marker image. The application detects this image which is supposed to lie on the floor or another horizontal surface, and displays the 3D model of the crucifix on top of it. An online questionnaire followed by a group interview with experts in the CH domain was conducted to discuss the AR prototype and the possibilities and challenges with the use of AR technology in digital CH. We focused on the context of Blekinge Museum exhibitions as an example of a regional museum. Four experts filled in the questionnaire and three of them participated in the group interview consisting of two stages. In the first part the experts were shown the AR prototype. This was followed by a group discussion mainly driven from the participants. In the second part the moderator presented additional considerations prepared in advance by the organisers by collecting personal reflections and information from background literature in the area of computer graphics applied to CH. The aim was to include a different perspective in the discussion and to gather insights about the potential differences and knowledge gaps between experts of different domains. Answers from the questionnaire and the group discussion highlighted established capability of AR technology such as exhibition enhancement and interaction, appealing to new target audiences and the possibility to display artefacts outside the museum: (i) expanding the geographic area of impact of the museum that aims at covering the regional territory, (ii) attracting visitors to the museum as sort of preview of the type of artefacts available on site. Regarding the challenges, much focus emerged on the cost of the technology, the necessity of building specific competence and expertise among the museum staff, and the usability and accessibility aspects of the AR applications. The Bring Your Own Device (BYOD) policy was mentioned as the ideal solution to tackle the problem of the costs of the devices which support also the usability since the visitors are more accustomed to handling their own devices. The BYOD policy implies the requirement of being available to the largest number of visitors, hence the AR application should be multiplatform and its availability should not be limited to the most recent and powerful mobile devices. Other mentioned challenges were the restricted computational resources of the devices and the necessity of applications maintenance (software updates). Aspects related to health and safety of sharing devices have also been discussed. The presented case study highlighted relevant aspects considered by the experts as well as providing new insights to take into account to make AR technology successful in virtual CH exhibitions of a regional museum. Future work will include improving the AR prototype adding interaction with the artefact, showcasing the AR prototype in the original location of the artefact to collect non-expert visitors expectations and run a usability study of the AR application. This work was supported in part by KK-stiftelsen Sweden, through the ViaTecH Synergy Project (contract 20170056).
Segmentation-Based Near-Lossless Compression of Multi-View Cultural Heritage Image Data
(The Eurographics Association, 2020) Buelow, Max von; Tausch, Reimar; Knauthe, Volker; Wirth, Tristan; Guthe, Stefan; Santos, Pedro; Fellner, Dieter W.; Spagnuolo, Michela and Melero, Francisco Javier
Cultural heritage preservation using photometric approaches received increasing significance in the past years. Capturing of these datasets is usually done with high-end cameras at maximum image resolution enabling high quality reconstruction results while leading to immense storage consumptions. In order to maintain archives of these datasets, compression is mandatory for storing them at reasonable cost. In this paper, we make use of the mostly static background of the capturing environment that does not directly contribute information to 3d reconstruction algorithms and therefore may be approximated using lossy techniques. We use a superpixel and figure-ground segmentation based near-lossless image compression algorithm that transparently decides if regions are relevant for later photometric reconstructions. This makes sure that the actual artifact or structured background parts are compressed with lossless techniques. Our algorithm achieves compression rates compared to the PNG image compression standard ranging from 1:2 to 1:4 depending on the artifact size.
Sunlight Simulation of the Church of Saint Nectaire in Virtual Reality: a Digital Time Machine
(The Eurographics Association, 2020) Saleri, Renato; Spagnuolo, Michela and Melero, Francisco Javier
The roman church of Saint Nectaire, like many churches in Auvergne, France, is richly decorated with carved capitals. Most of them represent figures or symbols of Christianity and are periodically illuminated by the sunlight that comes to strike them at different times of the day throughout the year. The periodicity of these occurrences, which seem to correspond to a "targeted" temporality around religious feasts, appeals to historians who foresee the possibility of a perpetual religious calendar marking the times of the Christian liturgy with regularity and precision. The observations made since 2009 by Daniel Tardy [Dan13] have made it possible to highlight the high number of luminous phenomena, particularly concerning the remarkable lighting of the choir capitals: this has made it possible to hypothesize peculiar coincidences between the day of the luminous event and the date of the Julian calendar (used from 46 B.C. to 1582 AD) corresponding to the Christian celebration of the illuminated figures. The presence of hills, however, recurrently masks the sun at the beginning and end of the day and prevents the illumination on a certain number of sculpted figures that one would expect, given the number of calendar occurrences already observed elsewhere. Considering its experience in the field of digital survey 3D modeling and real-time simulation in the field of heritage [ASL15], [MDSB14], [NMRS13], [SCN*13], [Sal18], the MAP laboratory created a complete numerical model of the church and to submit it to a virtual heliodon in order to predict the illumination of the interior decorative elements at "critical" moments throughout the year if the surrounding hills did not exist: the question of the primary location of the church is currently the subject of many conjectures. This experiment consists in a methodological approach whose purpose is to validate a solar simulation method on an existing building and to verify its validity by direct confrontation between the simulation produced and the observable effects in reality. This not only allows us to make hypotheses about the constructive history of the the church of Saint Nectaire, but also - in the near future- to apply this method to several nearby churches, similar in their history, their architecture and their religious iconography.

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