A 3D spatial data infrastructure for Mapping the Via Appia

Abstract

The use of 3D technologies in archaeology and architectural history has grown enormously. Nowadays, 3D technologies are used to record, present, analyse and reconstruct archaeological sites. Since the used tools mostly originate from other domains, the developments are characterised as technology-driven rather than methodology-driven. The recent trend of Free and Open Source Software (FOSS) and the technological improvements of digital infrastructures are changing this.

This article presents the development of a 3D Spatial Data Infrastructure (3D SDI) that allows archaeology and historical architecture researchers to analyse complex sites. For the development of the 3D SDI, IT literacy levels of the users, reusability of the tooling and the advantages of using FOSS are taken into account. The 3D SDI was developed for Mapping the Via Appia. An interdisciplinary team of archaeology experts and engineers have developed tailor-made 3D solutions to enhance the analysis and exploration of the Via Appia.

Introduction

Since the 1990s, the use of digital 3D technologies in archaeology and architectural history to study structures, sites and landscapes has grown considerably. Initially, these technologies were foremost used to present reconstructions. Looking back, these early virtual reconstructions are nowadays considered to have functioned more as illustration, rather than as coherent and scientifically transparent representations (Hermon, 2008, Frischer, 2008). This changed from the mid-2000s onwards with the introduction of advanced data capturing techniques, such as laser scanning and photogrammetry methods, together with the development of advanced software to handle and analyse 3D data sets. This has allowed and stimulated archaeology and architectural history scholars to explore and incorporate these technologies in their research. Regarding the various ways in which 3D technologies are applied nowadays four different uses can be distinguished.

• First, 3D technologies are used to virtually analyse reality-based data derived from fieldwork such as excavations and architectural and field surveys. These 3D data can either be newly produced by measuring objects or excavated layers in the field using photogrammetry and laser scanning techniques, or derived from vectorised 2D field drawings from both recent and past documentation activities. A key advantage of collecting and converting fieldwork data in 3D is that it allows researchers to virtually analyse three-dimensional relationships between layers, structures and objects. Furthermore, real-world distances, dimensions and volumes can be virtually measured, as such tools are incorporated in most 3D software. Additionally, most 3D documentation initiatives have applied 2D GIS strategies as their starting point, meaning that archaeological units and architectural and archaeological objects are digitally and spatially defined, to which relational databases containing structured information are linked. For querying this attributive information, existing 3D GIS software (e.g. ArcScene) or custom made tools are used (Dell´Unto et al., 2015, Forte et al., 2012, Von Schwerin et al., 2013).

• The second use of 3D technologies distinguished is to produce digital archaeological and architectural 3D reconstructions. For producing 3D reconstructions, objects from reality-based models are virtually repositioned or additional objects are created based on the researcher's interpretation (e.g. Dell’Unto et al., 2013; Schäfer et al., 2015; Guidi et al., 2009; Piccoli, 2014).

• Advanced 3D spatial analyses such as calculating line of sight, flooding, smoke, noise and smell, as well as spatiotemporal analysis such as simulating shadows and astronomical relations, are distinguished as the third way in which archaeology and architectural history scholars use 3D technologies. Noteworthy studies are Johanson and Frischer (2008) and Frischer and Fillwalk, 2013, Frischer and Fillwalk, 2014, in which hypotheses on alignments of reconstructed monuments to the sun have been tested in a virtual 3D environment, and the works by Paliou (2014) and Landeschi et al. (2016) on visibility analysis in reconstructed buildings.

• The fourth use of 3D technologies by archaeology and architectural history scholars is to present research results to other researchers and a broader audience. Already in the 1990s the value of 3D technologies for these purposes was noticed by Renfrew (1997). More recently, Frischer (2008) has stressed that computer modelling has become a standard application for archaeologists for presentation purposes. 3D technologies have also proved to be of value for educational purposes. The works of Forte et al. (2012) for Çatalhöyük and Liestøl (2014) alongside the Via Appia in Rome show interesting results on how virtual and augmented reality techniques can be used to present archaeological information to the public or archaeology students for educational purposes.

The various ways in which 3D technologies are used, as presented above, are strongly interwoven. Ideally one would use reality-based models as input for producing 3D reconstructions, applying basic measure and query tools as well as performing spatial and spatiotemporal analyses of them. The other way around, 3D reconstructions themselves can be used as input for advanced spatiotemporal analyses in order to test archaeological hypotheses, as demonstrated by Frischer and Fillwalk, 2013, Frischer and Fillwalk, 2014. Furthermore, the sharing and presenting of results to other researchers and the use of 3D technologies for educational purposes require input from the previously mentioned uses.

However, although the archaeological and architectural history studies using 3D technologies have increased and evolved considerably, the currently available software tools and the required IT skills by the various users are considered to form a limitation in exploiting the possibilities of 3D technologies within these domains. Especially for the study of large-scale, complex, archaeologically rich areas, the number of suitable and reusable tools is currently limited. To that extend, the MayaArch3D project (URL 1; Von Schwerin et al., 2013, Von Schwerin et al., 2016; Auer et al., 2014) has produced valuable prototypes in which a large-scale archaeological site can be analysed in a virtual 3D environment. They produced a data infrastructure for the ancient Maya site of Copan in Honduras, which can be accessed, visualised and analysed through various applications. To enable sharing they have focussed their development on online tools. Preliminary results from that project show that it assists researchers in expanding questions and developing new analytical methods.

The current article presents a similar and even complementary approach to the MayaArch3D project by discussing the development and implementation of a 3D Spatial Data Infrastructure (3D SDI) for the Mapping the Via Appia project. In the context of this article we consider a SDI to exist of user objectives, user IT literacy, content (data), technical components and governance (see De Kleijn et al., 2014). Mapping the Via Appia aims to analyse the complex and archaeologically rich area between the fifth and sixth mile of the Via Appia (Mols et al., 2013, Mols, 2014; URL 2). The 3D SDI has been developed by an interdisciplinary team of software engineers, archaeologists and architectural historians (Netherlands eScience Center, Spatial Information Laboratory and Radboud University). The development of the presented 3D SDI differs from previous studies by focussing on working with Free and Open Source Software (FOSS) and using the GitHub platform (URL 3) to publish the produced code. This way, the study aims to demonstrate the possibilities and opportunities this paradigm shift in computer software development has to offer for archaeological and historical architectural studies in which 3D technologies are used. The article shows that issues regarding collecting data, sharing data, processing complex data sets and dealing with diverse skill levels and needs of users can be handled by developing a 3D SDI using FOSS. We believe that this direction offers a solution towards the issue sketched by Forte et al. (2012) that most 3D applications used within the discipline are technology-driven, rather than driven by archaeological research methodologies (Forte et al., 2012). Applying FOSS allows for user centric development of 3D software for the archaeological and architectural history domain. Furthermore, since FOSS are free to be reused by others and since the code is publicly available, the article aims to demonstrate that this approach lowers the financial barrier, an issue that has also been identified by Dell´Unto et al. (2015).

The article is structured as follows. After a description of the study area of Mapping the Via Appia and the specific opportunities for 3D technologies to be of value in the context of the project, the outcomes of a user requirement analysis are presented. This is followed by a description of the applied data acquisition and processing methods. Next, the architecture of the infrastructure, its relation to the data acquisition methods and the clients on top of it are presented. By discussing these steps and the components that have been developed, the article offers an insight into how 3D technologies can be applied for studying complex sites by various users by approaching it as a 3D SDI using FOSS.