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4. 3D Web-based Visualisation and Cyber-Infrastructure in Archaeology and Cultural Heritage

So far we have described some case studies exemplifying a range of off-line visualisation systems available today. We will now consider recent efforts aimed at developing cyber-infrastructures for the on-line visualisation of 3D archaeological data. A workshop held at the National Sciences Foundation in February 2013 focused on the process of synthesis in archaeology, highlighting the need for investment in computational infrastructures that would assist in overcoming some of the archaeological 'grand challenges' that prevent synthetic research in archaeology. By which we mean problems of preservation, discovery and access, difficulties with data integration, the sheer variety and complexity of archaeological data and evidence, and the disciplinary norms and pragmatics of data sharing and collaboration (Kintigh et al. 2015, 4). This need to reconsider the nature of archaeological research was envisioned a few years ago by Ezra Zubrow, who stressed how I-archaeology would be relevant for an i-world; he argues that I-archaeology 'will change the way people conceive of the past for they will be connected to all of it all of the time if they so wish' (Zubrow 2010, 4).

Starting from the previous assumptions, it is critical to develop cyber-infrastructures that allow us to overcome the impediments to synthesis in archaeology described by Kintigh et al. (2015, 4). These cyber-infrastructures should allow access to a wide variety of data (i.e. 3D reproductions, 3D panoramic videos, RTI images, etc.) that reproduce the site or artefact as realistically and interactively as possible.

Such a 3D web-based visualisation system (3D viewer) should not only address the visualisation component but also be able to integrate a variety of datasets coming from fieldwork campaigns and include hyperlinks (i.e. links to pictures, 3D models, text, etc.). These should provide a range of audiences with varied information on the layers detected, excavation area, and methodologies used during fieldwork, and, in addition, links between the layers and artefacts or other material remains found on site etc. Mark Aldenderfer argues that 3D viewers should allow for simultaneous visualisation of 3D contents and all inferences enhanced by 3D replicas and simulations:

What I have in mind as a set of tools for visualisation in service of archaeological simulation doesn't really exist yet in our field. We must develop tools and approaches that allow us to simultaneously 'see' (i.e. to create images that may represent a wide variety of information content across a variety of media types) and to 'know' (i.e. to be able to connect these disparate images to other kinds of data) such that inference is enhanced and enabled (Aldenderfer 2010, 55).

In other words, this kind of interactive application should give scholars and the general public, as well as other stakeholders interested in these fields of study, the opportunity to access and visualise various datasets, favouring and enabling multiple interpretations of the same archaeological context and facilitating greater synthesis in archaeology as a result of better interconnectivity between researchers and practitioners in the fields of heritage and archaeology.

The visualisation of 3D contents was one of the main goals of the European-funded project CARARE. CARARE gave users the capability to visualise 3D models in real-time, but the information on these models can only be seen separately from the 3D models. In other words it is not possible to visualise 3D models and site information simultaneously.

The development of a complex real-time system for the data management, analysis, and visualisation of archaeological sites, using 3D realistic and metric reproduction of the archaeological units instead of schematic graphic representation, is a controversial and frequently discussed topic among digital archaeologists today. This is because the creation of a 3D web-based platform for the analysis and interpretation of archaeological data requires overcoming substantial technical and methodological challenges, including:

• the management of complex 3D models represents a key point for the creation of a usable and accessible visualisation platform;
• the 3D real-time visualisation system needs to be integrated with solid on-line information brokers and aggregators for different resources, since working in the context of 3D visualisation for digital archiving requires sustainability and long-term preservation and dissemination of the data;
• the development of a 3D web-based collaborative research platform needs to build on the availability of complex cyber-infrastructures, which integrate a realistic 3D visualisation of archaeological sites and related databases archived on-line;
• the collaborative platform should consider and solve the needs of scholars, researchers and practitioners from different fields working on the analysis and interpretation of all data collected on site.

As described above, complex visualisation systems already exist, but they are mainly off-line platforms designed to present monuments and archaeological sites to the general public. The challenge now is to combine this interaction, alongside analysis and interpretation of these virtual environments, with related datasets on the wider web. The creation of standardised and complex databases for the preservation and sharing of the archaeological record is becoming more widespread in archaeology. Two of the most important and successful examples of data services supporting research and education in archaeology are the Archaeology Data Service (ADS) and the Digital Archaeological Record (tDAR). The ADS was established in September 1996 at the University of York, while tDAR was developed at Arizona State University in 2008 as part of the Digital Antiquity initiative. There are also examples of European-funded projects that are trying to bring together and integrate existing archaeological research data infrastructures, such as the ARIADNE project (Niccolucci and Richards 2013).

This on-going commitment of the European Research Council to support cyber-infrastructures that enhance and promote access and preservation of European Cultural Heritage requires further research and improvements in the integration of the 3D component on the web. Although there have been some attempts to create prototype management systems for the visualisation of 3D representations of the archaeological record (Losier et al. 2007; Doneus et al. 2011; Stal et al. 2014; Trautner 2015), none of them is integrated within stable digital archives that allow for the long-term preservation and dissemination of those data.

As part of European efforts to design and develop complex cyber infrastructure, the European-funded project ADS 3D Viewer: a 3D Real-Time System for the Management and Analysis of Archaeological Data developed a 3D web-based resource for the management and analysis of archaeological data within the Archaeology Data Service. The ADS 3D viewer was created to take advantage of recent developments in web technology (Web Graphics Library: WebGL) by current web browsers. This project originates from an on-going collaboration between the ADS and the Visual Computing Lab (ISTI-CNR, Pisa) in the framework of the ARIADNE European project (Niccolucci and Richards 2013). Combining the potential of the 3D Heritage Online Presenter (3DHOP; Potenziani et al. 2015), a software package for the web-based visualisation of 3D geometries, with the infrastructure of the ADS repository, the 3D Viewer project created a platform for the visualisation and analysis of 3D data archived by the ADS (Galeazzi et al. 2016).

The methodology used in developing the 3D viewer was shaped by three main objectives:

1. 3D model optimisation. To provide a visualisation that can be used to access supporting data in the 3D view, it is first necessary to optimise the 3D models. The optimisation and management of complex 3D models acquired through laser scanning and image-based modelling is, in fact, the first challenge to overcome for the creation of usable and accessible visualisation programs. This task required collaboration between an archaeologist with extensive expertise in 3D documentation and data processing and the ADS archivist. The constant feedback of the ADS archivist was essential for understanding whether the format developed for, and supported by, the ADS 3D Viewer (NEXUS 2015) was appropriate for the long-term preservation of the 3D information. This stage was also useful in understanding how to re-use and optimise the data acquired for other purposes in previous projects (Galeazzi 2015).
2. 3D viewer development. The 3D models were imported into an off-line beta version of the 3D viewer to begin development of the different elements and tools of analysis of the infrastructure. In this second stage of the process the archaeologist/3D modeller received essential support from the 3DHOP developers and the ADS application developer for the creation of the infrastructure.
3. Standardisation of structures and formats: the ADS 3D viewer on the web. This part of the project involved integrating the off-line beta version of the viewer into the ADS on-line repository. A set of pilot tests was conducted on the off-line version of the viewer before its integration in the ADS infrastructure, in order to optimise it and facilitate its integration in the existing on-line aggregator's cyber-infrastructure. In this part of the project the archaeologist/3D modeller received support from various members of the ADS staff to archive a complex variety of data coming from the pilot case study used for the implementation of the viewer, including the digital archivists, the communications and access manager and the collections development manager.

The two versions of the viewer developed in this project, the Object Level 3D Viewer (implemented to extend the browsing capability of ADS project archives by enabling the visualisation of single 3D models) and the Stratigraphy 3D Viewer (implemented in order to allow the exploration of a specific kind of aggregated data: the multiple layers of an archaeological stratigraphic sequence), are designed to answer the different needs of users. These platforms allow those unable to participate directly in the fieldwork to access, analyse and re-interpret the archaeological context remotely, and are likely to help favourably transform the discipline, by nurturing inter-disciplinarity, and cross-border and 'at-distance' collaborative workflows. We are confident that the ADS 3D Viewer is a tool that could play a significant role in the integration of both traditional and innovative digital acquisition methods in day-to-day fieldwork practice.

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