The Use and Application of SfM-Based Documentation in Excavation and Standing Remains Assessment of the Stabian Baths, Pompeii

Abstract

The international research project ‘Bathing Culture and the Development of Urban Space in Pompeii’, headed by the Institute for Classical Archaeology of the Freie Universität Berlin, uses Structure from Motion (SfM) 3D models to record, document and analyse complex archaeological and architectural situations at the Stabian Baths in Pompeii. The paper presents case studies of the application of 3D models in archaeological and architectural contexts and highlights their potential not only as a documentation method, but also as analytical tools and key aids in publishing. It also draws attention to problems arising from work with large and complex digital datasets in interdisciplinary and international research teams and suggests potential solutions.

1 The Stabian Baths in Pompeii

Since 2015, a research project at the Freie Universität Berlin has been studying ‘Bathing Culture and the Development of Urban Space in Pompeii’, with a particular focus on two bathing complexes, the Republican and the Stabian Baths. Initially funded by and carried out within the framework of the German Excellence Cluster 264 Topoi (www.topoi.org/project/c-6-8/. Accessed 07 Oct 2020), since the termination of this cluster in 2019 the project has continued as a key international excavation conducted the Institute for Classical Archaeology at the Freie Universität Berlin, in cooperation with the University of Oxford (See https://www.geschkult.fu-berlin.de/e/klassarch/forschung/projekte/pompeji/index.html; https://www.topoi.org/project/c-6-8/. Accessed 07 Oct 2020). By studying the development, function and broader context of the two major early baths in Pompeii, the project seeks to provide new insights into the urban development of Republican Pompeii and the development of late Hellenistic and early Roman bathing culture (see Trümper et al. 2019).

The project encompasses excavation, full standing remains assessments and various scientific analyses of the archaeological records of both bathing complexes, including calcareous concretions from the baths, as well as wells and aquifers in their vicinity, and ash deposits. Within this framework, both digital and traditional analogue recording and documentation techniques are employed. The Republican Baths represent a traditional open archaeological site, since they no longer existed at the time of Pompeii’s destruction in AD 79 (see Trümper 2020), meaning that the extant remains can only be made visible through excavation. The Stabian Baths, by contrast, still stand largely. As a result, their study requires a highly complex process of excavation interlinked and entwined with standing remains assessments more akin to urban rescue excavations.

The sheer size and excellent state of preservation of this complex mean that traditional analogue documentation approaches frequently reach their limit, with digital methods coming to the fore. At the same time, the Stabian Baths raise specific research questions that test the limits even of digital documentation approaches. The following contribution concentrates on the potential of and problems arising from the use and application of three-dimensional documentation and data-analysis approaches in relation to the Stabian Baths – even if all of the theses and problems highlighted below are, of course, equally applicable to the Republican Baths.

2 Digital Methods Employed

When it comes to the application of digital documentation methods, the Stabian Baths are somewhat unique. The bathing complex has a long research history, meaning that the current project is a combination of new excavations, the re-excavation of earlier trenches and the re-evaluation of earlier archaeological work. For the earliest archaeological excavations, see Maiuri (1932) and, for a summary, Trümper et al. (2019, 103–106). The same is true of the architectural assessment of standing remains, which by and large involves a re-evaluation of earlier work, including fundamental treatises both on the development of Pompeii as a city and of Roman bathing culture in general (Eschebach 1970, 1979; Trümper et al. 2019, 108–127). At the same time, the assessment of the standing remains requires us to not only deal with original Roman structures, but also to separate these from all the modifications and repairs carried out since their rediscovery in the mid-nineteenth century. Here, the project can draw on an analogue collection of 42 detailed drawings documenting the state of the remains of the baths during the field seasons of Hans Eschebach in the 1970s (Eschebach 1979, Plates X–XX), with some dating all the way back to the Sulze/Eschebach campaigns of the late 1930s and 40s. That said, the actual genesis of these drawings is not always clear. Some plans show varying degrees of distortion, most likely caused by a combination of changing scales, analogue field documentation and print processes. A key problem is that the widely used overall ground plan of the Stabian Baths provided by Eschebach – which is the key base plan for contextualising all the different parts of this research project – diverges from the reality of the building in many places, sometimes significantly so (Trümper et al. 2019, 108–109). Moreover, these problems do not concern only the base-state plan of the remains of the Stabian baths, since, during the project, it became evident that practically none of the reconstruction drawings provided by Eschebach actually correspond with his base plan.

This state of affairs made it necessary to take a fundamental decision about how to deal with existing plans and documentation at the outset of the project. It would have been beyond the scope of the project to completely re-document the entire complex – which measures more than 3000 m² and, in some areas, exhibits unique levels of preservation of both structural remains and interior decoration – either by analogue means or by modern 3D-documentation technologies. As a compromise, a new georeferenced survey grid, which is independent of the old plans, was defined for the entire site. In addition, the project is able to draw on new and georeferenced state plans generated within the framework of the ‘Grande Progetto di Pompei’ on the basis of 3D laserscans. These made it possible to fully correct all the existing analogue documentation elements from Eschebach’s work. At key places, the corrected existing plans are supplemented with new analogue architectural drawings, 2D photogrammetries and 3D models (Fig. 4.1). While two-dimensional documentation is carried out using established methods based on total-station survey points, 3D documentation within the project is largely based on 3D photogrammetry using so-called ‘Structure from Motion’ (SfM).

Fig. 4.1

Project state plan of the Stabian Baths. The highlighted areas show parts of the complex documented using SfM modelling and case studies presented in this paper. (C. Brünenberg, based on Eschebach (1979), pl. 2 © FU Berlin)

Most of the interior walls of the men’s section of the Stabian Baths have been documented using photogrammetry, in order to enable an accurate understanding of the building phases and reconstruction of their appearance (Fig. 4.2). This method suggests itself, given the fact that these walls present almost plane surfaces. It is therefore applied wherever possible to the recording of plane surfaces. In addition, the project utilises SfM wherever the geometry of the extant spaces to be documented is highly complex. The archaeological component of the project utilises SfM models as an additional means of documenting excavation trenches (with traditional analogue documentation serving as a corrective), while the architectural analyses of standing remains use SfM modelling as a basis for specific room configurations, individual spaces or specific architectural features and details. With regard to both archaeological and architectural applications, it can clearly be shown that this approach to three-dimensional documentation is ideal for highly complex spaces and geometries.

Fig. 4.2

Photogrammetry of the west wall of the men’s tepidarium of the Stabian Baths. (C. Brünenberg, © FU Berlin)

The models used to date were recorded using two different camera systems, depending on whether they are archaeological or architectural in nature – corresponding to the two teams engaged on the project. Archaeological trenches and situations were recorded using a Canon EOS 550D SLR camera with a standard EFS18–55 Canon lens, while the architectural documentation team employed a Nikon D5100 SLR with a 35 mm prime lens, also from Nikon. The models were created and calculated using AgisoftPhotoscan and, from 2019 on, its successor software AgisoftMetashape. With one exception, all the archaeological models and most of the architectural models were accurately georeferenced within the new plans of the Stabian Baths. Only the model of the pool in the men’s tepidarium could not be georeferenced, because of its difficult local situation within an enclosed space and without stable surface to support a total station. This model was therefore referenced and scaled within a local system.

3 Case Study 1: Archaeology

For the excavation part of the project, traditional hand-documentation methods have been used. However, following a trial period of different digital documentation methods in the first field seasons in 2015, all of the project’s trenches are now documented as 3D SfM models upon completion of each excavation season – primarily as a project-internal study tool, since they enable virtual visits to the trenches, even after backfilling or if one is not physically present at Pompeii. In several instances, the models proved to be far more than study tools and have proved instrumental for understanding the trenches during post-excavation analysis and for visualising complicated situations in publications, as the following two examples show:

One key research question concerning the Stabian Baths is the role they played in the urban development of Pompeii, as they are widely believed to cover an area previously occupied by private housing, as well as the eastern fortification of the so-called ‘Altstadt’ of Archaic Pompeii (Robinson et al. 2021; Trümper et al. 2019, 103–105). In order to reassess this thesis, several open areas were excavated in the palaestra of the baths, including Area 3 – a stratigraphic reference trench that re-opened and extended earlier excavations, connecting the remains of the baths as they are seen today in the west with the remains of an earlier house, cutting across the area where the presumed Altstadt defences would have been found (Fig. 4.3).

Fig. 4.3

Area III, a stratigraphic reference trench across the central part of the palaestra of the Stabian Baths, in 2016. (C. Rummel, © FU Berlin)

At its greatest extent, the resulting excavation area measured 10 × 4 m, mostly in the form of a cross-stratigraphy cut that extended to a depth of 5 m in places, across a complicated series of intercutting pits and ditches, walls, potential wells and a drain. The trench included continuous archaeological sections more than 6 m wide and 5 m tall that proved challenging for analogue documentation – particularly given that the upper levels included important features located only centimetres apart that were impossible to draw at a scale that would enable the entire section to fit onto paper sheets of a manageable size. It was equally difficult to document the section photographically at the relevant level of detail (Fig. 4.4) and photogrammetry had to be excluded as the drain and remains of walls disrupted the plane surfaces of the trench sections. As a result, the georeferenced 3D model of the trench provided not only a simple means of visualising the section in its entirety with the required amount of detail (Fig. 4.5), but it also proved an indispensable tool in the study of this part of the archaeological record, its accuracy having been tested against analogue detail drawings. The key role of the 3D model in this particular instance is reflected in a recent project publication on the early urban development of Pompeii, which repeatedly draws on the model as a whole or sections of it as illustrations (Robinson et al. 2021, Figs. 16, 18, 21).

Fig. 4.4

Photograph of part of the S section of Area III in 2016. (C. Rummel, © FU Berlin)

Fig. 4.5

Orthophoto of the S Section of Area III, generated from the 3D SfM model. (A. Hoer, © FU Berlin, Pompeii Project)

While this instance of 3D documentation within the archaeological component of the project was merely a means to address the problem of how to document the smallest features within a large-scale archaeological record, the Stabian Baths frequently raise challenges for archaeological documentation, given the existence of spaces containing crucial archaeological information about the development of the baths that are so small or difficult to access that traditional documentation methods cannot be employed. A case in point is a series of small rooms along a corridor in the northern tract of the baths identified as N1-N4, which had previously been interpreted as ‘bathing cells’ (Eschebach 1979, 51–54; Trümper et al. 2019, 110–112, 127–140), based on the observation that each of these four rooms has a sump-drain in the north-west corner, as well as a small, c. 60 cm high internal wall dividing it into a wider western and narrower eastern part (Fig. 4.6). Eschebach took the latter to be bathtubs. As this part of the Stabian Baths is of central importance for understanding their establishment and early phases, two of the rooms were excavated within the framework of the project: cell N1 was re-excavated, having been cleared by Eschebach in the 1970s; cell N2 was newly investigated (Trümper et al. 2019, 127–140).

Fig. 4.6

Overview of one of the so-called ‘bathing cells’, room N2, from its entrance, after excavation. (C. Rummel, © FU Berlin)

While photographically documenting excavations of interior spaces measuring a mere 2 × 2 m was challenging, the interior dividing walls made this impossible in the smaller spaces to the east, which are only 40–56 cm wide (Fig. 4.7).

Fig. 4.7

The space east of the interior dividing wall of cell N2 after excavation. (C. Rummel, © FU Berlin)

During excavation, it became apparent that in order to understand how the baths were constructed, it was important to ascertain whether or not key fill levels of Cell N2 – one of the first parts of the baths to be built – varied between the western and eastern parts of the room. As a result, it was crucial to document both archaeological sections of levels between the interior dividing wall. In the eastern section, this proved practically impossible due to the limited space available. It was, however, possible to create a full 3D model of the room using SfM on the basis of 355 individual photos (2.7 GB), with a dense point cloud of 40,215,106 points and 8,042,983 faces (Fig. 4.8). An orthophoto of the eastern face of the interior dividing wall, as well as the archaeological strata beneath it, was created from this 2.7 GB model, upon which the stratigraphic sequence could be marked in the same way as on a section drawing (Fig. 4.9). It was only through the development of the georeferenced SfM model of this space that this part of the excavated stratigraphic sequence could be visualised for the publication of this crucial dataset concerning the establishment and early development of the entire complex (Trümper et al. 2019, 138, and Figs. 15a, 15b and 17).

Fig. 4.8

SfM generated model of cell N2 of the Stabian Baths. (T. Heide, © FU Berlin)

Fig. 4.9

Vertical section orthophoto of the east face and underlying stratigraphy of the dividing wall of cell N2 with highlighted stratigraphic units. (T. Heide, © FU Berlin)

4 Case Study 2: Documenting the Interior of the Men’s Section of the Stabian Baths as the Basis for an Architectural-Historical Analysis

The second case study from this project is intended to illustrate the approach, conditions and output of the SfM documentation and analysis of complicated standing remains. Within the framework of the project, it was the unique and often complex geometry of specific rooms, series of rooms or decorations of rooms that defined key parameters for 3D documentation within the framework of the assessment of standing remains. For example, the central heating furnace of the Stabian Baths, with insets for three hot water cauldrons, would have been virtually impossible to document using traditional, 2D approaches. As such, it was documented and analysed by means of a 3D model (Fig. 4.10). The main criterion for using 3D modelling as primary form of documentation was, however, an assessment of the potential added scientific value of such models on the basis of spatial analysis of the overall geometry of specific parts of the Stabian Baths.

Fig. 4.10

SfM model of the central heating furnace of the Stabian Baths. (C. Brünenberg, © FU Berlin)

The models presented here focus on the interior spaces of the men’s tract of the Stabian Baths, which, in their final phase, consisted of four main rooms (see Fig. 4.1). From the exterior spaces, bathers entered an elongated apodyterium or changing room. This gave access to the round frigidarium, or cold bath, as well as the tepidarium, or warm room. From here, it was possible to enter the caldarium, or hot room. From this typical sequence of Roman bathing rooms, both the apodyterium and frigidarium were documented in their entirety as SfM models (Figs. 4.11 and 4.12). Detail models of the eastern part of the tepidarium, including the pool and the western apse of the caldarium, highlight key features of these rooms.

Fig. 4.11

Interior view of the circular frigidarium of the men’s section of the Stabian Baths with wall decorations, SfM model. (C. Brünenberg, © FU Berlin)

Fig. 4.12

Video of the circular frigidarium. (C. Brünenberg)

Different considerations informed the choice to model only parts of these rooms: in the case of the rectangular tepidarium, all four walls were recorded by photogrammetry. Only the eastern part of the pool and its supporting hypocaust present an essential and complicated 3D structure (Figs. 4.13 and 4.14). As such, documenting the room in its entirety by photogrammetry would have led to a loss of information regarding the pool and heating system due to their complex geometry, while SfM modelling would have resulted in a dataset so large it would have been difficult, if not impossible, to handle.

Fig. 4.13

SfM model of the pool and hypocaust heating system in the eastern part of the warm room, the tepidarium of the men’s section of the Stabian Baths. (C. Brünenberg, © FU Berlin)

Fig. 4.14

Video of the pool inside the men’s section tepidarium. (C. Brünenberg)

This resulted in a hybrid approach. The apsidal western part of the caldarium, with its centrally positioned labrum, as well as the eastern part with a large hypocaust-supported pool include complicated 3D structures. While documenting the apsidal western part did not present any problems (Figs. 4.15 and 4.16), the pool and its immediate environs are extremely fragile and could only be recorded without accessing them directly, i.e. by means of an unmanned aerial vehicle or similar equipment.

Fig. 4.15

SfM model of the apse at the western end of the caldarium of the men’s section of the Stabian Baths, including the central labrum. (C. Brünenberg, © FU Berlin)

Fig. 4.16

Video of the apse and labrum inside the caldarium in the men’s section. (C. Brünenberg)

A key factor in the 3D documentation approaches used in the project is ‘level of detail’ (LoD). A major aim in modelling the apodyterium and frigidarium was to produce an accurate representation of their overall spatial geometry and exact relationship to one another. To achieve this, the models were calculated to a level that accurately reflects these relationships, but that does not include every minute detail, so as to ensure the usability of the models. That said, the raw data allow for modelling at a significantly higher level of detail, if required. The other two models discussed here were created to document all remaining architectural and structural details as accurately as possible. Thus, only relevant parts were modelled in order to maintain data usability. The different purposes served by the models are directly reflected in the number of polygons (or faces) in each model, as can be seen from the core data of the four models discussed (Table 4.1).

Table 4.1 Core data for the architectural models under discussion in this paper

But how exactly can such models advance our understanding and the possibilities of standing remains analyses, particularly beyond the levels achieved by traditional methods of two-dimensional documentation? The answer is to be found in the project’s core research question, which can be subdivided into two categories, at least with regard to the study of the standing remains. On the one hand, the project seeks to analyse information about the materials used, the decorative programmes employed, the use of colour and other related aspects of individual rooms, as well as of the complex as a whole. These aspects can, to a large extent, be studied and analysed by means of traditional two-dimensional recording and documentation techniques. The other key aim is, however, to develop a detailed understanding of building techniques and their application in three-dimensional space, in order to be able to reconstruct building phases and processes. In concrete terms, this means that the models discussed can be interrogated in light of specific research questions:

• Stabian Baths, frigidarium: before this room was transformed to house the cold pool, it served as a laconicum (Eschebach 1979, 58–59; Trümper et al. 2019, 148–149, note 123) covered by a pointed cone roof. Eschebach describes this as ‘[…] konstruktiv leichter aus[zu]führen als eine Halbkugel […]. Der Konus ist über einem Lehrgerüst geformt […].’ (Eschebach 1979, 59). The use of such a shoring or sub-structure during construction is highly questionable in architectural-historical terms, as it is often the very lack of such a structure that leads to a vault shape of this kind. It is only through an analysis of the overall geometry of the room and its vault that reliable and grounded architectural interpretations can be formulated with regard to this key constructional question.

• Stabian Baths, tepidarium, pool: one important part of the project is the reconstruction of the water supply and heating systems of the baths. The pool in the tepidarium is not only a key nodal point in both of these systems, but also of direct relevance for understanding the development of the baths. An analysis of the precise relationship between the pool and the eastern wall, which was broken through in order to accommodate the water supply and heating systems, as well as the surrounding hypocaust system, can provide insights into the planning and execution of these supply systems.

• Stabian Baths, caldarium, apse: the western part of the caldarium was remodelled at some point, with the west wall being dismantled to accommodate the addition of an apse. It is likely that as part of this modification, the entire room was equipped with a wall-heating system consisting primarily of tegulae-mammatae, tiles and spacers that created an artificial level of air along the walls of the room, as well as tubuli. The imprints of these spacers can still clearly be identified on the interior faces of the walls of the apse of the caldarium (Fig. 4.15). The precise positioning of these spacers, as well as the surviving ventilation shafts (blue highlights), make it possible to reconstruct not only the design and function of this system, but also the actual process of construction and thus its economics, i.e. the quantities of building materials involved, etc.

5 3D Documentation and Associated Data Beyond Field Seasons and Project Phases: Open Questions

As we have seen, 3D modelling has significant potential – and not only as a documentation tool, as it was frequently employed in the course of this project. Added scientific value can be derived from 3D models of archaeological and architectural situations, if they are correctly recorded and applied. However, models, in particular, are not necessarily easily exchanged and transferred during the evaluation phase of a project, and there are significant issues with their long-term and post-project use, publication, archiving and longevity.

Most archaeological projects have at least one common denominator, and this is also true of the project presented here: during the data-generation phase, i.e. the field seasons at Pompeii, project members are able to focus their entire attention on the object or theme of study, often on-site. The recording and documentation of study objects, including the generation of raw data for SfM modelling, is carried out on-site during these project phases. In most cases, however, post-processing of data does not occur on-site, and often it does not even occur during the field seasons. It is frequently the case that preliminary models are generated in order to minimise errors or to enable re-documentation in case problems arise. In all of the case studies presented above, the final models that were used for study and/or publication were calculated and generated only subsequently, during post-processing phases in Germany, often sometime after the field season in which the data was recorded. As the project involves a large interdisciplinary and international team (see Acknowledgements), this requires a highly structured and advanced technical workflow and exchange mechanism, enabling all the project members to access project data – whether they are based in Berlin, Oxford, Frankfurt, Darmstadt, Freiburg, Lübeck, Naples or elsewhere. This is particularly true given that, as is often the case, the technical structures of the project changed, developed and evolved over time (Trümper et al. 2019, 105) and large datasets can no longer be exchanged and transferred by traditional and direct means. At present, the project has not yet fully processed all the 3D models for which datasets have been recorded, but it is possible to present a first overview of the data involved and in use at present (Table 4.2).

Table 4.2 Current project data amounts and requirements for SfM models

The size of the data package for the processed models, at roughly 700 GB (as at 2020), may appear impressive, but it is, in fact, a normal feature of projects involving 3D documentation. The treatment of such datasets within the framework of multi-institutional cooperation projects, however, might be challenging. Should all data be stored on a single central server? Which project partner owns the rights to digital data? Do the rights remain with the relevant heritage-management bodies (as is the case in some states and countries), do they belong to the institution carrying out the research project (be they universities, research institutes or private companies) or do funding bodies, private foundations in particular, in effect ‘buy’ the rights to digital data? Moreover, which legal framework for digital data is decisive for a project with international partners? That of the lead partner?

How, then, are access rights and channels for external project members structured? Are data to be exchanged in the course of a project? If so, how are they maintained and kept updated? There are also issues that go beyond these practical problems, such as the hardware provision of data-hosting institutions: should this be used for the calculation and generation of models at all times during projects, e.g. following software updates of key programs? In part, such problems can only be addressed by the compulsory inclusion of data-management plans in future project applications (Forschungsdatenmanagement, or FDM, in the case of German funding bodies) and their consistent application – an idealistic position that, sadly, too often succumbs to the daily realities of scientific practice.

Consistent data management and curation is of critical importance, and not only for project-internal reasons. Research and analysis rely on well-curated and well-organised datasets, but of equal significance is the question of the use and archiving of data after a project has concluded, i.e. that of the longevity of 3D data. The connected and digitised modern scientific world has made it a declared goal to archive and provide access to all relevant project data. In other words, not only the highest-resolution models are to be published, but access should be provided to all raw data, including photographs, survey points and interim states of model generation. While this will no doubt enable subsequent generations of researchers to utilise this data – either by means of new technologies or for the study of entirely new aspects – it results in even larger datasets. However, this much-vaunted goal remains, at present, just as hypothetical in nature as the hope for the sustainable implementation of data-management plans. As such, it is important to address a number of issues that are currently at best only partially resolved:

If the public availability of data is a key aim, the licensing of datasets is necessary. CC licensing offers numerous possibilities in this context, but is it a useful approach for all institutions? Independent research institutions, for example, may favour different licensing models than university libraries do (DNB 2017). However, it is the latter institutions, in particular, that represent the great hope for the long-term archiving and usability of research data in general and 3D-modelling data in particular. While such difficulties may seem academic when compared to the issue of data use in proprietary formats – at present, most of the archaeological and architectural-historical community (including this project) favour, with good reason, proprietary software from providers such as Agisoft, Autodesk and Adobe – the question remains of the issues this raises when it comes to the long-term usage and, especially, archiving of this data. A commonly advocated, but infrequently implemented solution is to require consistent archiving of the versions of programs used, in addition to the raw data (see Rimkus et al. 2014, www.forschungsdaten.info. Accessed 06 Oct 2020).

It is evident that these complex sets of problems cannot be resolved by individual projects alone. However, setting up a reasonable data and data-management structure at the outset, or ideally even in advance of a project, has now become a necessity. Depending on the size of the objects to be documented, data-management structures and workflows must be adjusted. Especially when dealing with immobile objects, such as architecture, key factors in successful documentation include: the scope of the documentation (e.g. full, sections or details), georeferencing (GPS or GCP data available), avoiding fragmentation caused by immoveable objects (e.g. vegetation) or inaccessible parts (e.g. roofs, dangerous building segments) and the classification of 3D models (e.g. walls, doors and building materials). Whilst these points apply mostly to the preparation of projects or field seasons, more general questions come to light after the initial documentation has been completed. In addition to the aforementioned problems of saving, storing and archiving 3D data, the publication of 3D data remains a contentious, unclear and largely unaddressed issue. Several proprietary platforms (e.g. Sketchfab, Agisoft) and publishers offer promising and easy solutions, but sustainability and copyright issues are often considered causes for concern. Alongside proprietary solutions, the only fully functional open-source solution at this point is 3DHOP (as at 2020), a powerful HTML-based 3D Webviewer, which was developed in Italy at the Visual Computing Lab of the Institute for Information Science and Technologies (http://3dhop.net/. Accessed 07 Oct 2020). In Germany, the Deutsche Forschungsgemeinschaft (DFG) has launched a programme to develop a sustainable national data infrastructure (NFDI: https://www.nfdi.de/. Accessed 06 Oct 2020), which represents a clear step towards creating larger overarching structures to address these issues. This programme, naturally, deals with a much larger and more fundamental issue than merely the use and application of 3D modelling data. How, then, are we to deal with this, beyond the gradual evolution of project structures, ad hoc responsive solutions and widespread capitulation in view of giant datasets?

One solution we would like to propose is the establishment and standardisation of model servers in university libraries that include multiple access points that are restricted to certain users during project periods, but open access thereafter. Such an approach would, however, necessitate the processing and curation of data while the project is running. To what extent this is feasible currently depends as much on individual choice and priorities as data exchange and international licensing do. Several initiatives, including the development of iDAIworld by German Archaeological Institute, an open-source platform tool linked to DAI-held data, ranging from images, objects, structures and collections to geographic and bibliographical data and DAI publications, as well as 3D data (see https://idai.world/. Accessed 07 Oct 2020), and dedicated archaeological programmes developed for the NFDI initiative a consortium of archaeological research institutions and universities (see https://www.nfdi4objects.net. Accessed 04 Sep 2023) are actively involved in addressing this issue and devising potential solution models, in order to provide guidelines and frameworks that can be used by individual projects.