3D Reconstruction of the Renaissance Bastion of the Langenbrücker Gate in Lemgo (Germany)

This is the eleventh in a series of posts exploring 3D modeling in Mediterranean and European archaeology. For more in this series click here. We hope these papers will start a discussion either in the comments of the blog or on Twitter using the #3DMedArch hashtag.

Guido Nockemann, Freelance Archaeologist, AMD Nockemann,

In the beginning of the 16th century up until the Thirty Years War, the city of Lemgo was turned into a Renaissance fortress with a rampart, trench and bastions – unfortunately it was never finished. The southern entrance to the city was a bastion bathed by the river Bega with an associated gate construction with rampart and outer bailey on the city side (fig. 1).

Pic 1 LennepstichFigure 1: The Langenbrücker gate on a copperplate print of Elias and Henry van Lennep, about 1663

During archaeological excavations from 2009 to 2011 in preparation for constructions of the Langenbrücker Gate, remains of a Renaissance bastion were uncovered. They uncovered the massive counter bearings of the former bridge, wall remains of the outer bailey, torwange, curbstones of the gate, remains of the foundation of the gate tower of the bastion, wall fragments of the northern part of the bastion and parts of the side walls (fig. 2 and fig. 3).

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Figure 2: Southern abutment of the bridge and wall remains of the bastion (picture: Guido Nockemann)

Pic 3 WiderlagerFigure 3: Northern abutment of the bridge (picture: Guido Nockemann)

To present the results of the excavation to the public in a better way a 3D reconstruction of the southwestern part of the town fortification of Lemgo was established. It is based on the archaeological finds of the excavation as well as on historic plans and records (fig. 4). The point of time presented is around 1646, the end of the Thirty Years War, because the majority of data comes from that period. The archaeological evidence, however, is problematic due to consistent constructions for over hundreds of years and the historic tradition is inconsistent. Historic drawings of the city are often idealized and do not necessary correspond to reality. Different illustrators at different points in time drew, to some extend, very different views of the city e.g. in roofing, variation and size of towers. Information from historic records and city maps were taken into consideration in establishing the model.

Pic 4 StadtansichtFigure 4: Detail of a cityscape of the city of Lemgo south, 1 Half of the 18th century

A scale floor plan was used as a base for the 3D model considering every data accessible. If there was more than one possibility to solve a problem of detailing, the most likely one was taken. Historic photographs of parts of the town fortification, still existing in the 19th century, were a huge help.

Overlapping old city maps with archaeological finds showed anomalies which can be explained by the inaccurate measurement methods of that time. If there were not any archaeological evidence for walls or buildings, their position had to be interpolated. While reconstructing the structures above ground, data from records and from drawings of the city could be used. As there are no hints to the materials used for the finishing of the fortification and buildings, no photorealistic textures were used in the model. With a button, the actual archaeological finds can be made visible in the 3D model (figs. 5 and 6).

Pic 5 3D RekonstruktionFigure 5: 3D reconstruction of the bastion and gate system at the Langenbrücker gate (graphic: Morris Viaden – Kleinkino / Medienproduktion)

Pic 6 3D Rekonstruction 2Figure 6: Detail of the 3D reconstruction (graphic: Morris Viaden – Kleinkino / Medienproduktion)

An introductory text is essential for the visitors to explain the basis for the reconstruction was established. The main problem with that is, to a scientist, a 3D model is just one way of interpreting finds, but the general public will take that model for “scientific evidence and truth”. It should be stressed in the description, that the model is just one possible appearance, even if it is a very likely one, of the fortification of the city of Lemgo.

References:

• Guido Nockemann (in press): Die 3D-Rekonstruktion der renaissancezeitlichen Festungsanlage am Langenbrücker Tor in Lemgo, in: Archäologie in Westfalen-Lippe

• Guido Nockemann (2012): Lemgo – Langenbrücker Tor; Ergebnisse der archäologischen Untersuchungen, Kampagnen 2010 / 2011 (Online-Presentation: http://www.lemgo.net/fileadmin/image/redakteure/planungsamt/Denkmalpflege/Ausgrabung_Langenbruecker-Tor_2012.pdf)

• Link to the 3D-Rekonstruktion: http://www.lemgo.net/fileadmin/image/redakteure/planungsamt/flash/lemgo3d.html

The Work of Archaeology in the Age of Digital Surrogacy

This is the tenth in a series of posts exploring 3D modeling in Mediterranean and European archaeology. For more in this series click here. We hope these papers will start a discussion either in the comments of the blog or on Twitter using the #3DMedArch hashtag.

Adam Rabinowitz, The University of Texas at Austin

I’m very glad that Bill has run this series of 3D Thursday blog posts, because they have demonstrated with particular clarity that field archaeology is at a turning-point in its engagement with three-dimensional visualization. A decade ago, a series of posts on 3D technologies in archaeology would have been concerned mainly with computer-aided virtual reconstructions and immersive environments or with the use of laser scanners. This series, however, has highlighted an emerging common interest in the use of computational photography to create photorealistic 3D representations of archaeological material. 

3DThrusday

Previous posts have emphasized the way new software and methods have lowered the bar for the creation of high-quality 3D or 2.5D models of physical objects. James Newhard suggests that these tools are becoming wrenches in the standard archaeologist’s toolkit, and I think this trend is likely to intensify over the next decade, especially as drone-based photography becomes a matter of course. Such tools offer two enormous advantages: the enrichment of data collection in the field, which in turn enhances the archaeologist’s interpretive process (a point made by Brandon Olson, Rachel Opitz, and Eric Poehler); and the ability to make distant objects available for scholarly autopsy, as Dimitri Nakassis argues in his post on Reflectance Transformation Imaging. As an added benefit, quick, cheap 3D representations created through computational photography provide a new way for mass audiences to engage with the physicality and materiality of objects, both in an academic publishing environment, as Andrew Reinhard enthusiastically affirms, and, as Sebastian Heath demonstrates, in connection with active excavations and museum collections as well. That last point was driven home just yesterday by the public launch of the Smithsonian X 3D project, which presents models of objects in the institute’s collections, complete with downloads suitable for 3D printing (though it must be noted that most of this data was captured by more traditional laser scanning). 

These contributions also highlight the extraordinary extent to which this shift has been driven by just two recent developments: the popularization of the Polynomial Texture Mapping algorithm developed by Tom Malzbender (Malzbender, Gelb, and Wolters 2001), in large part through the efforts of Cultural Heritage Imaging; and the rapid improvement of the algorithms that produce 3D models using structure-from-motion (sometimes casually referred to as “photogrammetry”), represented particularly by Agisoft’s Photoscan software and Autodesk’s 123DCatch app. Many of us had carried out experiments with computational photography and structure-from-motion in the early 2000s (e.g. Tschauner and Siveroni Salinas 2007; Rabinowitz et al. 2007), but the new tools have transformed a laborious manual process involving a certain amount of technical expertise in both image capture and transformation into a fully automated workflow that even corrects for the defects of the photographer (see now De Reu et al. 2013 and Olson et al. 2013).

Pmp CH06SR 84 m

3D model of bedrock features uncovered at Chersonesos in the 2006 field season, created from photos with PhotoModeler Pro. The model was georeferenced in ESRI’s ArcScene, and then exported to a 3D PDF using Adobe Acrobat 9 Professional Extended (sadly no longer available).
Click to download the 3D Pdf 

The attraction is powerful: unlike conjectural 3D reconstructions or the pure geometry offered by laser-scan point clouds, computational photography seems to promise unmediated access to the physical reality of existing material remains. As Heath points out, and as can be seen even more dramatically in the recent use of Google Glass to capture a 3D digital model of a head of Marcus Aurelius in the Walters Art Gallery, the technology also offers significant possibilities for open access and democratization. Anyone with a smartphone with a camera and a few minutes can create a passable 3D model of an archaeological object or work of art and post it online. The examples below give a sense of the variability in the effort required and the quality of the results. Above is a model of a cast of the Belvedere Torso in the Blanton Museum of Art, created in the space of about five minutes with 16 hasty photographs taken with an iPhone and processed with AutoDesk’s 123DCatch app. Below is a model of an inscription found at Troy and now held by the UT Department of Classics — this more careful representation involved 37 photographs and a light source, and took about 20 minutes to create, again with 123DCatch.

Belvedere Torso

Belvedere Torso (Click to view in 3D)

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Photogrammetrical model of Troy inscription (Click to view in 3D)

I’ve called these 3D digital objects “models” and “representations”, but they are perhaps more accurately described as “digital surrogates”. “Digital surrogate” is a term of art used in the libraries and archives to refer to any digital representation of a work that exists in the physical world (a thumbnail, a metadata record, a digital image). More commonly, however, the term indicates a faithful digital copy that seeks to represent an analogue original as accurately and in as much detail as possible: “By definition, a surrogate can be used in place of the original. If a surrogate is electronic, the same files can be used both internally (to protect the original when the surrogate is of sufficient quality and accuracy to stand in place of the original), and externally (to provide wider access for those who might otherwise be unable to view or study an original)” (Grycz 2006, 34). 

Not all surrogates are “of sufficient quality” to serve as substitutes for originals, of course, and there is still a lot of discussion about the extent to which even the highest-resolution scan can replace contact with an original document (the term is almost always used to talk about two-dimensional objects like manuscripts or photographs). Nevertheless, the notion of the “digital surrogate” reflects an underlying assumption that a digital reproduction ought to be able to stand in for the real thing — and therefore it is particularly appropriate for three-dimensional digital objects that seek to reproduce the visual and spatial characteristics of objects in the real world. A good surrogate isn’t merely a copy: it is supposed to provide, in some sense, access to the original, now made ubiquitous and opened for inspection on a level of detail that the original itself might not allow. Brandon Olson makes just such a point in his reflections on the use of 3D models in the first post of this series.

Popular accounts of the rise of computational photography already treat the surrogate as if it provided access to the reality of the physical original. In the most recent issue of Archaeology, for example, a brief article on the use of drone photography in Peru concludes with the excavator’s somewhat breathless claim that “[y]ou can model every single stone” of a site (Swaminathan 2013). And even sober NPR correspondent Robert Siegel, covering the Smithsonian 3D project, is compelled to ask whether digital reproduction techniques will become so good that they will allow the creation of perfect “forgeries” that are indistinguishable from the originals. But when we look at these surrogates, are we really being afforded closer contact with reality? Or do these exciting, rapid, “disruptive” (to use a word very much of the moment) changes mask some underlying epistemological and methodological problems? I think it’s worth attempting to establish a theoretical framework to help us understand not only the benefits conferred by these technological advances, but also what is really happening as we leap from original to digital surrogate.

A starting point for this discussion is offered by Walter Benjamin’s oft-cited essay “The Work of Art in the Age of Mechanical Reproduction”, in which the cultural critic reacts to the impact of new technologies on the social role of Art (with a capital “A”). These new technologies made possible the large-scale dissemination of faithful representations of unique artworks and the exploration of visual phenomena that could not be captured through ordinary perception. Benjamin was concerned that such reproductions would destroy what he called the “aura” of original, “authentic” works of art: that is, the artwork’s “presence in time and space, its unique existence at the place where it happens to be” (Benjamin 1968, 220). The availability of copies, mass-produced for mass consumption, led to “the desire of contemporary masses to bring things ‘closer’ spatially and humanly, which is just as ardent as their bent toward overcoming the uniqueness of every reality by accepting its reproduction.” “Every day,” he continues, “the urge grows stronger to get hold of an object at very close range by way of its likeness, its reproduction” (223).

The essay was published in 1936, and the new technologies that inspired Benjamin’s concerns were  photography and its offshoot, cinema. But he might as well be speaking of the three-dimensional representations of ancient “originals” that many of the posts in this series focus on. The mechanical reproduction has given way to the digital surrogate — a representation of an analog original in the form of the ones and zeroes of binary code — but less has changed in the last 80 years than one might expect, especially since these digital surrogates continue to be generated with the same old new technology of photography. 

The effects of digital surrogates mirror those Benjamin ascribes to photography and film: they distance us from the unique physical thing-ness of that which they represent while allowing us to manipulate reality in ways that the original would not permit. Compare, for example, his claim that the “enlargement of a snapshot does not simply render more precise what in any case was visible, though unclear: it reveals entirely new structural formations of the subject” (236) with Eric Poehler’s statement that 3D surrogates of Pompeian architecture allow views that would not be physically possible for an observer present in person. Or compare the 3D isolation of stratigraphic sequences that Rachel Opitz describes, free from extraneous layers, excavators, plants, tools, etc., with Benjamin’s comment on the invisibility in movies of the cameras, lights, and personnel needed to make them: “[t]he equipment-free aspect of reality here has become the height of artifice” (233).

Two fundamental points emerge from Benjamin’s critique. One is that a surrogate is not the original, nor does it represent reality: it is the product of “artifice”, of techniques and processes that are themselves not visible in the end product. The other is that photography is fundamentally different from earlier two-dimensional copying techniques: “for the first time in the process of pictorial reproduction, photography freed the hand of the most important artistic functions which henceforth devolved only upon the eye looking into a lens” (219). He has in mind techniques like woodcuts and engravings, which produced multiple copies of a single original. The engraved original itself might be a reproduction of an existing work of art — but in that case, too, the engraving was also an artistic interpretation, not a straightforward reproduction, and the product of the creativity and skill of the engraver (Fyfe 2004).  

Image

Engraving depicting an intaglio gem from von Stosch’s collection, from Winckelmann’s 1760 publication. This “digital surrogate” of the printed illustration is housed in the Arachne database of the German Archaeological Institute, where it is also linked to records associated with the publication, the original gem, and casts of gem impressions.

The tension between original and reproduction, art and artifice, access and authenticity, is not a new one in Mediterranean archaeology. In fact, long before the discovery of photography, the birth of ancient art history was entwined with the creation of 3D surrogates through increasingly mechanical means. In the Renaissance and the early Baroque period, sculptors like Bernini prided themselves on their ability to imitate or add to ancient sculptures, and gem-cutters produced new intaglio gemstones based on Greek and Roman originals. By the 17th century, however, broader interest in Classical Antiquity and its iconography led to a market for casts of impressions from the ancient gems themselves. These casts were collected in dactyliothecae that served as iconographic encyclopedias (Knüppel 2009). Dactyliothecae functioned in the same way as the digital 3D surrogates  we’ve been discussing: they allowed the close study of 1:1 representations of absent objects to extract “authentic” visual information, and they offered mass access to originals that were scattered among different collections across Europe. At the same time, large-scale ancient sculpture was also being cast in plaster, again to allow the experience of the “real” (or hyper-real!) form and volume of absent originals and to permit the centralized collection of works otherwise dispersed in geographic space (Borbein 2000). 

The mechanical reproduction processes involved meant that casts of gem impressions and sculptures were usually at a scale of more or less 1:1, which added to the sense of access to an original. That impression was reinforced by artifice as well: casts of sculpture could be acquired with various finishes meant to evoke marble patinas, different stones, even metals. Here, however, we move from authenticity to verisimilitude — that is, the finishes didn’t necessary reproduce the appearance of the original, but evoked the way an object like this was supposed to look. The distinction between truth and truthiness extended to the form of sculptural casts as well. Because so many of the sculptures reproduced were already Roman “reproductions” of Greek statues, they existed in multiple exemplars, each of which might have better preserved components (one might have a head but no arms, another arms but no head, etc.). Some casts were thus actually amalgams of the best-preserved parts of different originals. In other cases, minor additions or changes were made to better suit the appearance of the reproduction to the tastes or expectations of the consumer. The introduction of these modifications during the technical process that created the cast is invisible to the viewer. Instead, changes made to make a cast look more “Classical” shape in turn our notion of what the “Classical” is supposed to look like. For all the use of mechanical reproduction, then, these apparently straightforward surrogates have a problematic relationship with their originals.

If casts offer a Victorian analogy for the 3D digital surrogates created with structure-from-motion algorithms, the venerable paper-pulp epigraphic squeeze is the analog ancestor of the reflectance transformation image. Again, the crucial quality of the squeeze is its mechanical reproduction, at a 1:1 scale, of the physical surface features of the original, without the interpretive intervention involved in the publication of measurements and transcriptions. Squeezes were generally produced by and for scholars, and were not subject to the sorts of interventions that casts are. On the other hand, the quality of a given squeeze depends on the technical abilities and equipment of the squeeze-maker. Like casts, then, squeezes are not simply “physical surrogates” for originals, but objects of artifice derived from originals through specific processes mediated by their creators and often conditioned by preconceived ideas about how the final product should look. 

I have spent this time on physical 3D surrogates for two reasons. First, they highlight the importance of scale and measurement for the usefulness of a surrogate. Squeezes and casts are valuable precisely because they are 1:1 in scale, and can thus allow measurement of the original by proxy. Second, as Benjamin argues for mechanical reproductions in general, they have a problematic relationship with their originals. On one hand, some surrogates have preserved information about originals that are now lost or damaged — early examples of the LOCKSS (Lots of Copies Keeps Stuff Safe) principle. And squeezes continue to be used by epigraphers for off-site study of inscriptions, even when the original still exists. On the other hand, plaster casts have had a generally unsuccessful run. After being introduced as better representations of the reality of the originals than the originals themselves in the 18th century, they had fallen out of favor by the middle of the 20th, perhaps in part as a result of the concern of critics like Benjamin with authenticity and “aura”. Many collections were destroyed; others persisted in a sort of half-life as curiosities, but not as resources for scholarly inquiry. 

Fundamentally, casts have not been able to maintain their initial value as “cultural capital”, in sociologist Pierre Bourdieu’s sense. This is in part due to their diffusion, which makes it difficult to control their use as symbols of distinction: the cultural capital provided by a full-scale cast of the Farnese Hercules is somewhat diminished by the existence of the SkyMall version. But it is also due to the opacity of the process by which they were created and the lack of information about the context of that creation. This is true of all varieties of physical 3D surrogate. A cast made for the tastes of the commercial market may not be trustworthy for academic research, and a squeeze made by an untrained beginner may be a poor representation of the original.

The history of these physical surrogates and Benjamin’s critique of mechanical reproduction offer us a foundation for a more considered approach to digital 3D surrogates. I’d like to conclude with two starting points for further theorization and discussion.

First, I think it will be of fundamental importance to remember that the digital 3D model is not a true surrogate for the original, even when derived from photographs. This is particularly true for models of archaeological remains in the process of excavation, which will never again be available for first-hand autopsy. I would argue, therefore, that it will be critical not to throw out the handicraft in archaeological documentation — the measured hand-drawn plans and interpretive sketches that, like engravings of artworks, admit that they are representations that seek to highlight the choices and ideas of the creator, and do not claim to be mechanical reproductions of objective reality. Rachel Optiz makes the same observation in her post, and I think it’s supported by a growing body of research on the special ways in which our brains interact with drawing surfaces and writing instruments (we need more studies on haptics and embodied cognition in archaeology!). It would be a grave mistake to lose the skills necessary to create interpretive drawings in our rush to adopt quick, easy, and powerful computational-photographic methods.

Second, I would like to propose a set of four basic principles for publication and archiving to ensure the future scholarly usefulness of the 3D digital surrogates derived from computational photography. Some of these are already in place, at least in some forward-looking projects; others will require the development of new tools. All of them, I think, will be extremely important as computational-photographic methods become more powerful, more democratic, and more black-boxy for most users. 

1) Measurement. To ensure that scholars can reuse the 3D data you’re generating, the models have to include some user-accessible information about scale and units, ideally in the form of both in-interface measurement tools and a platform-independent marker (like a clearly-marked meter stick included in the image). This seems like an easy one, but it’s trickier than it looks. Andrew Reinhard noted that keeping scale constant would be hard across different publication formats, and the models of the portico and the marble feet in Sebastian Heath’s post highlight the effects of lack of scale. When we consult 2D documentation, we frequently make our own measurements using either the scale statements or the scale bars provided in the illustration. In order to be truly useful, 3D model-delivery platforms must offer the same opportunities (Adobe’s 3D PDFs include a measurement tool, but the basic Unity interface and p3d.in do not).  

2) Raw data. I feel that we are ethically bound to provide not only models, but our original raw data for reuse wherever possible. The importance of this — and the problems with access that turns out to be open in name only — has been reinforced by a recent case involving CyArk and proprietary control of laser-scanning data (for details, see the original post here, with additional discussion here). These digital objects are at least one step closer to the reality of the original, and they also make it possible to reprocess the data as more powerful tools and algorithms come online.

3) Metadata. The raw data, of course, are of little use without comprehensive metadata that not only describe file formats, creation dates, etc., but also indicate what those raw data represent. This is going to be especially important for the enormous batches of photographs generated for the purposes of computational photography. It’s great if the final model has metadata that tell us it’s a Pompeiian building — but I would argue that we need to ensure that every photograph in the sequence has metadata that describes at least the technical details of the photographic file AND the basic identifying information for the object or monument it represents AND the context of its creation, including date, actors, project, etc.

4) Process history. A 3D digital surrogate isn’t the same as the physical original not just because of its format, but because it is the product of the computational manipulation of a series of intervening digital surrogates, whether photographs or laser scans. Our ability to trust and use the model depends on our ability to trace — and ideally to walk back — the processes by which it was generated, including parameters, assumptions, and fudges. Systems must be in place to capture and store this information so that users in the future will understand how a model was produced and therefore how it can or cannot be used. Cultural Heritage Imaging has made a lot of progress toward this goal with their work on empirical provenience and the “digital lab notebook”, and I would like to see similar practices adopted by all archaeological and heritage projects that use computational photography.

These principles come with a handy acronym: MRMPH, recognizable as the noise you make when you’re asked a question while taking a really large bite of something or while just waking up (I’ve never been good at generating slick acronyms). In all seriousness, though, the application of these principles to the publication and archiving of 3D digital surrogates will mark a watershed in archaeology: it will be the first time since the birth of our discipline that the archaeological record will grow richer, rather than poorer, with age, since new algorithms and software will permit the ever-more precise and accurate reprocessing of digital photographs for the extraction of 3D information. As 3D printing takes off, we will also have a new opportunity to recreate the archaeological record through widely available physical surrogates, which offer their own advantages for accessibility and interpretation. All this will be possible, however, only if we recognize with Walter Benjamin that reproductions cannot be stand-ins for originals, and acknowledge that digital surrogates in particular have their own independent reality as objects or works requiring their own documentation and explanation (Manovich 2001; Cameron 2007). 

Author biography: Adam Rabinowitz is an Assistant Professor in the Department of Classics at The University of Texas at Austin and the Assistant Director of UT’s Institute of Classical Archaeology.

Works cited

Benjamin, W. 1968 [1936]. “The Work of Art in the Age of Mechanical Reproduction.” Reprinted in H. Arendt, ed., Illuminations. Essays and Reflections, translated by H. Zohn. New York: Schocken Books, 217-251.

Borbein, A. 2000. “Zur Geschichte der Wertschätzung und Verwendung von Gipsabgüssen antiker Skulpturen (insbesondere in Deutschland und in Berlin).” In H. Lavagne and F. Queyrel, eds., Les moulages de sculptures antiques et l’histoire de l’archéologie. Actes du colloque international Paris, 24 octobre 1997. Geneva, 29-43. Text translated by B. Frischer, available at: http://www.digitalsculpture.org/casts/borbein/.

Cameron, F. 2007. “Beyond the Cult of the Replicant–Museums and Historical Digital Objects: Traditional Concerns, New Discourses.” In F. Cameron and S. Kenderdine, eds., Theorizing Digital Cultural Heritage. A Critical Discourse. Cambridge and London: The MIT Press, 49-76.

de Reu, J., G. Plets, G. Verhoeven, P. De Smedt, M. Bats, B. Cherrett, W. De Maeyer, J. Deconynck, D. Herremans, P. Laloo, M. Van Meirvenne, and W. De Clercq. 2013. “Towards a Three-Dimensional Cost-Effective Registration of the Archaeological Heritage.” Journal of Archaeological Science 40: 1108-1121.

Fyfe, G. 2004. “Reproductions, Cultural Capital, and Museums: Aspects of the Culture of Copies.” museum and society 2, 1: 47-67.

Grycz, C. J. 2006. “Digitising Rare Books and Manuscripts.” In L. W. MacDonald, ed., Digital Heritage. London: Elsevier, 33-68.

Knüppel, H. C. 2009. Daktyliotheken: Konzepte einer historischen Publikationsform. Rutzen.

Malzbender, T., D. Gelb, and H. Wolters. 2001. “Polynomial Texture Maps.” In Proceedings of the 28th Annual Conference on Computer Graphics and Interactive Techniques. ACM, 519-528. Available at http://www.hpl.hp.com/research/ptm/papers/ptm.pdf.

Manovich, L. 2001. The Language of New Media. Cambridge: The MIT Press.

Olson, B. R., R. A. Placchetti, J. Quartermaine, and A. E. Killebrew. 2013. “The Tel Akko Total Archaeology Project (Akko, Israel): Assessing the Suitability of Multi-Scale 3D Field Recording in Archaeology.” Journal of Field Archaeology 38: 244-262.

Rabinowitz, A., S. Eve, and J. Trelogan. 2007. “Precision, accuracy, and the fate of the data: experiments in site recording at Chersonesos, Ukraine.” In J. Clark and E. Hagemeister, eds., Digital Discovery: Exploring New Frontiers in Human Heritage, CAA 2006. Budapest: Archeolingua, 243-256.

Swaminathan, N. 2013. “Drones Enter the Archaeologist’s Toolkit.” Archaeology 66, 6: 22.

Tschauner, H., and S. Siveroni Salinas. 2007. “Stratigraphic modeling and 3D spatial analysis using photogrammetry and octree spatial decomposition.” In J. Clark and E. Hagemeister, eds., Digital Discovery: Exploring New Frontiers in Human Heritage, CAA 2006. Budapest: Archeolingua, 256-270.

 

Three- and Four-Dimensional Archaeological Publication

This is the ninth in a series of posts exploring 3D modeling in Mediterranean and European archaeology. For more in this series click here. We hope these papers will start a discussion either in the comments of the blog or on Twitter using the #3DMedArch hashtag.

Andrew Reinhard, Director of Publications, American School of Classical Studies at Athens

I have been the Director of Publications for the American School of Classical Studies at Athens (ASCSA) for just over three years, and am responsible for publishing our quarterly journal, Hesperia, as well as excavation monographs for Ancient Corinth, the Athenian Agora, and affiliated sites, plus Hesperia Supplements on special archaeological topics, as well as guidebooks and limited series. The views that I express in this post are my own, but it is my hope that various, official ASCSA boards and committees will agree with me on at least some of these points, creating new policy and modifying the old, as the press works with archaeologists to create the next generation of archaeological publications.

3DThrusday

Historically archaeology has been limited (and some could argue continues to be limited) to two-dimensional publication in print. Journals and monographs are traditionally printed and include commentary, catalogue, concordances, various front and back matter, tables, photographs of objects and of sites (mostly black-and-white, but occasionally color), drawings (plans, sections, profiles, etc.), and maps.

In recent years, some journals and books have been released as “digital editions” onto platforms such as JSTOR, Cambridge Journals Online, and through various publisher websites. By and large, these digital editions do not take advantage of any of the possibilities afforded by appearing on the Internet, being merely one-to-one digital reproductions of their original print counterparts. Readers can choose to read articles in print or on-screen. Those readers who opt to read on-screen do so either because they are traveling (or are away from their offices/libraries), or because their libraries only have digital versions of publications. These digital publications are either served online in an HTML page-view or as PDFs, occasionally in other formats, rarely sharable or even printable because of outdated digital rights management (DRM) and copy protection “safeguards”. In the case of PDFs (and devices and apps used to read them), readers are generally unaware of added functionality offered to these “flat” publications: document-searching, bookmarking, note-taking, emailing. I argue that for your average reader of archaeological scholarship, they are, and will remain oblivious, stuck in Flatland, unable to comprehend all the practicality that extra-dimensional publication can offer (and is already beginning to offer).

Taking the aforementioned elements of print publication of archaeological material, let us first apply a three-dimensional filter, followed by a fourth-dimensional one:

Text:

It would seem obvious that text is text, that it is by its nature two-dimensional. The writer writes what the reader reads. Writing an article or a monograph is a one-way form of communication. However, if one extracts this text from its two-dimensional setting and places it online, that text has the native ability to become something more. The content gains context. One can embed links reaching out to Open Access data repositories for people- and place-data. Making this publication available online also facilitates linking in the opposite direction, making the author’s content discoverable by anyone in the world, provided the text is given a stable URI. Widgets are now available that enable readers to roll over a placename and retrieve a pop-up window with a map and data along with a clickable link. In time, I hope to see a similar widget crawl through bibliographies and citations in notes, allowing readers to reference cited material as they proceed through the book or article. How often have you, as a reader, wished to check a reference or look up a place, but have instead put it off, not wanting to trek to the library or even run a Google search? Embedding these links and reading tools are a service to readers and are becoming increasingly easy to implement from an author’s/publisher’s perspective.

This “multi-dimensional” text takes what is good about the printed word, and adds practical improvements that help deliver more robust content more quickly to the reader:

Note-taking on the printed page is limited to the space in the margins or between the lines. Note-taking on a digital document allows for notes of massive length that can then be emailed/shared outside of that document. If you lose your book, you lose your notes. Digital editions allow you to save a “clean” copy as well as an annotated copy, and if you email/share your comments, losing your annotated copy is only an inconvenience, not a disaster.

What if we could go one step further, making the author’s primary text “four-dimensional?” In physics, three dimensions incorporate length, width, and depth. Add time to a three-dimensional thing, and it now has a fourth-dimension. All objects exist in space-time, and as the arrow of time moves us forward year by year, those three-dimensional objects change. While this observation will be more readily applied to imaging artifacts, we can apply the four-dimensional concept to an author’s text.

A published monograph is like a finished temple. It’s as good as the makers can produce at the time. As time moves along, things happen to the building. It can receive additions. It can be shored up. It might be demolished, lending its parts as spolia to other structures in future times. As archaeologists, we can also reduce the structure to its individual parts, seeing how the whole was completed, and also understanding how that building changed over time, from realized vision to revered monument, or derelict footprint. 

It is a misconception that a published monograph or article is the “final publication” of archaeological material. Upon publication, that text (and its related content of photos, maps, tables, etc.) becomes the starting point for rigorous discussion and dialogue. In the past, some journals have published rebuttals to earlier articles in later issues, a kind of time-delayed chess match. By integrating online publication with mature social networking/commentary technology, those discussions can be opened to a global audience. Should a counter-argument be made successfully, it is also possible for the author to make a change to the main text, or to add new bibliography, and to update notes over time, keeping current with future scholarship. The content of the published piece must change over time, and opening that content up to scrutiny can help to either preserve and promote excellent scholarship, or to mend, repair, or demolish research.

Seeing text as four-dimensional also allows the readers to uncover the foundations of an archaeological publication. In the instances of preliminary excavation reports or “final” reports of a class of objects from a site, I would strongly urge authors to provide their readers with complete data sets. This data can be checked, and can be used as a reference by readers. Should errors be discovered in the math and logic of tables, these can be corrected right away. And should there be a difference of opinion between author and reader, the data can be consulted, and a dialogue started. With traditional publication, the reader is presented with the author’s interpretation of the data, and that interpretation might or might not be reliable and might include biases, either conscious or unconscious. Opening up the data, and opening up the dialogue can help an author’s argument become more objective.

Tables:

A mixture of text and graphical elements (i.e., lines, shading, etc.), tables convey quantifiable data to support the author’s arguments, and to also relay in a readable form what was found over the course of a season, or of a decades-long excavation. In two-dimensional publishing, the table is printed on the page, or over one or several spreads, with a caption, headings, and notes. In three-dimensional online publishing, that table becomes a live data element able to be manipulated by the reader. With an interactive table, one can choose to sort data within columns, can rearrange columns, and can conceivably perform mathematic operations with the data, treating the table like a live spreadsheet. It’s likely that readers will have questions that the author did not think to ask, and providing the data in this interactive way can help readers ask and answer queries independent of the author’s commentary on the static table.

Dealing with data than cat be played with in a tabular format is not enough. To be a truly useful, living archaeological publication, its tables need to become four-dimensional, introducing the time element. Archaeology is notoriously messy and inexact, and our publications do their best to make sense of the mess. It’s likely that some material gets left out of a publication for whatever reason, or in the case of some excavations, material (e.g., lamps, coins, etc.) that is assigned only covers a range of years from that excavation. Any material excavated after the time period assigned to one researcher is dumped into a future publication. With an online “monograph”, newly recovered material (or material from years after an original assignment) can be added to the data set from which our interactive tables produce information for the reader. By allowing a publication to remain open, new data can be entered upon discovery.

These kinds of edits and on-the-fly make it difficult to identify the “version of record,” that version which is cited by other scholars when completing their own research. I propose that we follow the model used in wikis where a date/time-stamp and author ID are assigned whenever a page changes, and that the researchers citing that page include the date on which that page was accessed. If that is too extreme, then perhaps the software model can be followed wherein iterations (updates) are assigned incremental numbers whenever something changes in the code.

Maps:

Maps work perfectly well in two-dimensional, print publications, but being able to bring them online in 3-D is a necessity, especially when trying to understand the topography of a settlement, city, or region. By visualizing the geographic setting, both authors and readers can begin to draw conclusions about the placement of settlements (or structures within them), and how they relate to natural features in the landscape. Authors can also choose to indicate on maps where artifacts were recovered, where features like graves, pits, wells, etc., are located, all on a sliding scale for granularity depending on the kind of access granted to the reader. It’s possible that sensitive data such as findspots can be abused, so it may be that some level of security will need to be supplied to screen readers, or more simply, the excavation, its authors, and the publisher exercise common sense in determining how fine a grain is good enough for most readers while giving them the option to contact the excavation for permission to access to-the-centimeter map data.

While three-dimensional maps are crucial to archaeological publications, again, adding the element of time to online maps should be required. Some sites existed for periods of months or years, while others spanned decades, centuries, and millennia. For those sites that have experienced long periods of occupation, their maps should include a “timeline slider”. Readers can use the slider to watch the site change dynamically from decade to decade, period to period. Stopping time on the map, one can then observe features, and could conceivably tap or click on those to drill down to more information. As excavation proceeds and more data are collected and published, these maps will change automatically, including the new data input by the excavators over the course of a season. Three-dimensional maps are important and provide a snapshot of a site or region in time, but making the maps temporally dynamic can provide maximum use for readers and they consider new questions or conceive new hypotheses based on their observations of the maps and the data they provide.

Images:

Traditional, two-dimensional drawings are extraordinarily useful when communicating the profile of pottery, of the preserved letter forms in an inscription in stone, and designs and decorations, among other things. Print publications make frequent use of these, complementing the black-and-white drawings with black-and-white photos (aka “halftones”) that provide additional visual data of excavations and their artifacts either as they are, or as they were. Printing in color is expensive, and archaeologists are often charged by their publishers should they wish to have some “art” appear in color for their article or book. It would seem that economics has had an adverse effect on imaging archaeology in print, preventing color from being used when it might have provided additional (or different) data not communicated from an image in grayscale. Online publication completely removes economics from the decision-making process of choosing whether something should be illustrated in color or not.

I defer to other authors whom Bill Caraher has invited to write about 3-D archaeology and imaging to write about how they use it and the technologies employed to create 3-D maps, scans, reproductions, etc. It should be obvious to the reader that a 3-D scan of an artifact provides information that a 2-D drawing or photograph cannot. There are Open Source utilities now available that can rotate two-dimensional pottery profiles, creating a three-dimensional image to allow the reader to fully visualize what pottery, lamps, etc., would have looked like in the round. The problem remains that even with three-dimensional views and reconstructions, they are still viewed through two-dimensional media: screens. This is not unlike printing a three-dimensional image in a book, although at least with online 3-D imagery, one can pan/zoom/rotate.

I propose that for 3-D images to be truly useful to the reader, that they be printed via 3-D printers, based on printer specs provided to the reader by the author/publisher. Imagine printing your own set of plates, or printing bones/fragments, or even a scale model of a house or temple. Traditional photography and drawing work well when providing their data via traditional, two-dimensional media. 3-D imaging, to be most useful, should require either 3-D printing, or the use of glasses or headgear such as Oculus Rift to provide an immersive 3-D experience. 

As for four-dimensional aspects of imaging, it’s possible to include the time element when looking at a site over a period of years as it has undergone excavation, or in some cases, how a city has grown around an ancient monument. For 3-D reconstructions, a time slider could be used to view reconstructions of buildings or settlements throughout different periods. There are likely other applications that I’m missing, but I suspect others have already posed this question and come up with answers.

With digital imaging in electronic publications, there is one major issue that must be considered: scale. In a print monograph, the publisher sizes an image on the page and then prints the scale of the object in the image caption. Some publishers opt to include scale bars in their images, while others crop the scale bar out, relying on the caption to tell the reader what the size of the object pictured is. Because the printed page is static, the image size never changes. On e-readers, however (including smartphones, tablets, laptops, desktop computers, and e-book readers), the “page” and the image are resized constantly. Printing the scale in a caption doesn’t help, and leaving the scalebar in the image approaches the ridiculous as either tiny or large depending on how the reader resizes a drawing or photo. It may be possible to create a widget that dynamically changes the scale of the image based on its relative size on a screen. As a reader increases an image’s size for a better look at a detail, the scale would change from 1:3 to 3:1. Until that happens (unless it already has), readers might have to go on the measurements of an imaged artifact that are printed in the body or catalogue text and then eyeball the image to guestimate its actual size.

One potentially unexpected barrier to publishing archaeological material fully (and freely) online is that of image permissions. Countries such as Greece and Turkey have yet to update their guidelines for image permissions to include the current state of digital and online publication, especially for scholarly purposes. Greece’s Archaeological Receipts Fund (TAP) currently defines an electronic publication as a webpage and makes no provision for e-books or other kinds of digital media. It’s either a website, or it isn’t, and if it is, you can have permission to post that image for a maximum of three years before Greece, as the rights-holder of any image taken of any monument/artifact in-country, requires you to take it down. On the form to request permission from Greece to publish an image of a monument or artifact via digital media is language stating to the effect that it might take months for the bureaucracy to consider the application at which point it could either be rejected or a permissions fee assessed. There is little hope in Greece’s current state that this issue will be addressed; it’s the least of that country’s worries.

Conclusion:

Archaeology is messy, and it deals with three-dimensional artifacts in four-dimensional space-time. Its publications should reflect that. At our current level of technology, it is possible to create archaeological publications in an open, online environment that incorporates text, 2- and 3-D imagery, interactive 2- and 3-D maps, and interactive data sets, and omni-directional links to content and context managed by others. Our new publications must incorporate all of these elements to create a record and interpretation of what we have discovered, leaving that data and interpretation open to criticism, dialogue, and growth over time. Universities, archaeological field schools, and publishers need to make a concerted effort to educate archaeologists to the potential provided by new media and existing technology as it can serve to document work done. The editor’s role should be to apply standards and style, to fact-check, to clean up inconsistencies, to verify and standardize notes and bibliography, at which point it can be published, handed over to the crowd for the necessary, but until now missing step of post-publication peer review.

3D Imaging in Mediterranean Archaeology: What are we doing, anyway?

This is the eighth in a series of posts exploring 3D modeling in Mediterranean and European archaeology. For more on this project click here. We hope these papers will start a discussion either in the comments of the blog or on Twitter using the #3DMedArch hashtag.

James Newhard, Associate Professor, Department of Classics, College of Charleston

I come to the topic of 3D imagery from the perspective largely of the ‘end user.’ While I’m involved with projects that are capturing and using 3D imagery (such as the Palace of Nestor Linear B project), my expertise does not lie in this area. As such, my perspective and contributions lie on the level of one who sees 3D imagery largely in the context of its use, and in the broader context of digital applications in archaeology.

3DThrusday

To be fair, I have a notorious quirk. I can overlook easily the next great thing (in 1989, I announced to my friends that electronic mail ‘chatting’ was foolish and a waste of time, when a simple telephone bolted onto a wall would do just fine if not better). It usually takes me a period of time between being introduced to a new application, before suddenly – miraculously, even – rediscovering it and seeing not only its utility but near necessity. Similar stories can be told of my first contact with PDAs, multispectral satellite imagery, LiDAR, tablets, smart phones, and (gasp) GIS.
Some would call this quirk a fault. I would call it a bit of pragmatism. The world is full of toys these days. Innovation is all around us and there is an urge towards the faster, smaller (or bigger), thinner. Many crave hardware and software that can hold more, process more, and in general find the answer quicker than ever with more data than ever before considered.

But what’s the question? Why do all this? To what end?

Over the past couple of years, there has been an efflorescence of visualization applications. Photogrammetry, 3D imaging, GIS, and other approaches have increasingly taken on usage, to the point that they are beginning to be viewed as a common part of the archaeological toolkit.

I have a couple of questions about these new tools, and will endeavor to supply some answers:

1. In what part of the toolkit to these tools lie? Are they like my wrench set, or more like the $50 thingy I bought for that one project, and won’t need again?

2. How are these tools to be used? Collect and present data? As questions and evaluate answers? A little bit of everything?

3. Do these new tools come with instructions? Are they for everyone to use, or are they specialized tools, best left in the hands of professionals? Who are the professionals, anyway, and how do I either become or obtain one?

To help answer these questions, it is useful to take stock of where we sit in the development of 3D imagery and its applications. I view it as typical of the way technologies have often entered usage; a few brave souls engage in the medium at an early stage, but are rather alone in the world, owing to the steep learning curve of the program and a sense of limited application to questions that are more easily addressed via other means. With time, the software becomes more user-friendly and cheaper, allowing more people to experiment and play. Applications of the method still tend to be ‘carryovers” from earlier – in the case of GIS, mylar-layer maps were replaced by digital layers. In the third phase, the software and basic applications have become pervasive enough that people start to become formally trained in the applications, and begin to think of the innovation in terms of added value. Again, in the case of GIS – moving from the display of information to modelling, hypothesis generation, and testing.

In regards to 3D imagery, the Mediterranean world seems to be largely in the second phase of development. Software and imaging capture have become widely accessible, and we’ve moved beyond the initial ‘pioneer’ phase where a few intrepid scholars spent hours with clunky GUIs to effect rough approximations of reality. The vast majority of applications of 3D imagery still reside in the realm of display and presentation. Incredibly refined and detailed, surely, but largely the digital equivalent of 3D dioramas of bygone ages.

In terms of what kinds of tools we are dealing with, it would appear that the methods are becoming more like a wrench set and less like a specialized, expensive tool rarely used. Increasingly accessible by the rank and file archaeologist, their greater applications beyond basic rendering still remain in the hands of specialists, although forming collaborative teams of people is a time-worn trail of overcoming these hurdles.

Next Steps in 3D

As we gain facility in attaching data to our representations, moving from a presentation/display mode to one that is involved in dynamic modeling should be engaged. Alternatively, as 3D modelling becomes more commonplace, a system by which the various parameters that went into the model could be formalized and adjustable by the end user, much in the way that current models in GIS can be set up such that an individual need not know the methods to render, yet with a few inputs or choices, be in in the role of questioning and discovery.

I see several trends in or applications of 3D imagery:

1. Physics/engineering: If we can reconstruct structures in form, we can further use models to explain the relationship between form and function.. Using physics, one could use 3D imagery to analyse the strength of structures, thereby shedding light upon a variety of questions – the capabilities of buildings to withstand various levels of earthquakes, for example.

2. Metrics: How many pots do we have? The gain from digitizing artifacts in 3D – even the lowly body sherd, is that surface area and thicknesses are readily obtained. For periods where standard sizes of wares are known, one could compute the amount of material recovered of a particular ware type and get a sense of how much is represented. In addition to other information normally collected (number of rims, weights, etc.) this information could be added to provide additional measurables useful for ascribing function to space.

In cases where ware types are ill-defined, such metrics could be useful for retrieving data helpful for classification purposes and addressing issues of specialization and other topics related to the organization of production (Karasik 2012)

3. Viewsheds/cityscapes: With the capacity for building up, the opportunity to understand the built landscape is even more possible. The more that the base model mimics the actual environmental conditions, studies that model lines of sight and viewsheds will become most effective.

4. Gaming/engagement/education: The great draw of 3D imagery is in its ability to engage. There’s nothing wrong with that – in fact, there is a lot of good. As a form of dissemination that presents in an instant the cumulative knowledge of the research, these applications are powerful. Using 3D as a means to communicate and engage is an important element of the process, long overlooked in a discipline that rewards monographs and articles over media that is approachable by the lay person. For both the lay and professional, these products are effective communication devices in their own right.

Overriding all of these applications is the notion of modeling – using the available information to construct a hypothetical that is in some way reflective, iterative, testable. Ultimately, I view the development of methods in modelling a major goal – the purpose of data collection, after all, is to answer a question. Modelling provides a means by which data can be structured so as to allow a reflexive approach to hypothesis assessment and re-evaluation. 3D imagery fits within phases of model development, assessment, and eventual dissemination/communication.

Who’s going to do this?

We are situated at a time of transformation – when society as a whole moves from analog to digital, and information has increased in quantity, availability of access, and speed of delivery. From my high school graduation, I received a word processor. I bought my first computer as a wedding present upon graduation from college. I made my first website near the end of my Ph.D. Most of my research and organizational skills were ‘born analog.’ Not so the next generation of scholars. In the last 20 years, the information age has transformed how we obtain, manipulate, and disseminate our ideas. How has our training of the next generation changed? One would look long and hard for required courses in GIS or database development (although they are encouraged in many places). As I’ve argued elsewhere (2012, 2013), we need to think hard about how to bring out formal introduction of the modern tools of our trade into the training of the next generation. Otherwise, we run the risk of having others make the tools for us. Recent comments by Davis and others (2013a,b) have noted that the fields of archaeology and classics are changing in terms of the approaches used, but that our institutional guidelines/curricula are sometimes ill-matched to this new reality. New tools and approaches call for new training, which we have always done. The extent to which we have been beset with innovation, however, calls for serious discussions at the undergraduate and graduate levels in regards to what range of tools the next generation of archaeologist is expected to know, and at the professional level in terms of understanding what the outputs of research are and how they are best evaluated.

Archaeology, by its very nature, is a data-laden spatial enterprise. Context is everything, and that context has an X, Y, and Z coordinate. 3D is inherent to our work of understanding the past. We are drawn to these tools as a way to communicate our interpretations in the most accurate way possible. There are more possibilities beyond description and communication. Just as our earliest work in GIS was to communicate and describe, so too have been our initial forays into the third dimension. The next step, like GIS , is to move in the direction of using these applications to hypothesize, model, test, re-evaluate, and disseminate.

Mediterranean archaeology, as both an early and late adopter with its wide array of evidence, stands to contribute greatly to this next phase of discovery.
Provided, that is, that we allow ourselves to go there.

Works cited

Davis, J.L. 2013a. ‘Barbarians at the Gate,’ September 1, 2013. From the Archivist’s Notebook: Blog. Available from http://nataliavogeikoff.com. September 5, 2013.

Davis, J.L. 2013b. ‘Barbarians at the Gate: Comments on Comments,’ September 15, 2013. From the Archivist’s Notebook: Blog. Available from http://nataliavogeikoff.com. September 15, 2013. /

Karasik, A., 2012. ‘Computerized Documentation and Analysis of Archaeological Artifacts,’ paper presented at the Redford Conference in Archaeology. University of Puget Sound, Tacoma, Washington. Oct. 26-27, 2012.

Newhard, J.M.L. 2012. ‘Convergence,’ February 14, 2002. AIA Geospatial Interest Group: Blog. February 14, 2012. http://aiageo.wordpress.com

Newhard, J.M.L. 2013. ‘Archaeology, Humanities, and Data Science’ August 1, 2013. The Archaeoinformant: Blog. August 1, 2013. http://blogs.cofc.edu/thearchaeoinformant

Photogrammetry on the Pompeii Quadriporticus Project

This is the seventh in a series of posts exploring 3D modeling in Mediterranean and European archaeology. For more on this project click here. We hope these papers will start a discussion either in the comments of the blog or on Twitter using the #3DMedArch hashtag.

Eric Poehler, Assistant Professor, Department of Classics, University of Massachusetts, Amherst. 

3DThrusday

Since the inception of the Pompeii Quadriporticus Project in 2010, my co-director Steven Ellis and I have been exploring the use of photogrammetry to document one of the largest monumental structures at Pompeii as part of a comprehensive digital approach to the archaeological and architectural study of this building. Our approach has attempted to integrate photogrammetry with other imaging methods, including laser scanning and ground penetrating RADAR, as well as more traditional fieldwork digital products, such as standard photography, layered vector drawings, Harris matrices, and database records. The role that photogrammetry played in this campaign has expanded exponentially over the past four field seasons (on Photogrammetry at Pompeii, see Poehler and Ellis 2012, 3, n. 6). What follows is a discussion of our experiences, our current process, and some of the pitfalls and benefits we’ve encountered.

Fig 1 Quad and context balloon flight 3 IMG 8345 smerFigure 1

Before discussing our use of photogrammetry, a brief introduction to the site and our project is in order. The Quadriporticus (Fig. 1), traditionally called the Caserma dei Gladiatori or Barracks of the Gladiators, is structurally rather simple: a rectangular courtyard surrounded on four sides by 74 Doric columns with dozens of small rooms behind the porticos. The building’s original design, its evolution, and its impact on the landscape of Pompeii are, however, quite complex. The Quadriporticus was also one of the earliest parts of Pompeii to be excavated. Excavation of the building had begun by February, 1767 and the clearing of the porticos and surrounding rooms continued through 1805. It was not until approximately 1819 that the great mound of debris was removed from the center of the courtyard. The Quadriporticus therefore has long served as part of both the tourist infrastructure and the tourist’s image of ancient Pompeii. Indeed, by 1792 a portion of the roof and second story had been restored and toilet facilities put in place. Today, no less than a third of the more than people 2.5 million people who visit Pompeii enter through the Quadriporticus each year (World Heritage Centre/ICOMOS report, 7-10 Janurary 2013, 43) and the only signage any of those visitors will find still reads “toilets”. These facts, redoubled by the constant threat of another major earthquake (on the 1980 earthquake damage, see Adam and Frizot 1983) that could level the site or an eruption of Vesuvius that might once again bury it completely, make our responsibility to record this building with as much detail and as much clarity as possible all the more urgent. The cork model of Pompeii, completed in 1879, stands as a testament to the value of pushing recording technologies beyond what is considered adequate for its time. With each day, more frescoes fade, more tesserae fall out of mosaics, and more walls collapse leaving the cork model as one of if not the only record of their former state. The ease, speed, and low-cost of photogrammetry has made it one of our most important tools to create a near-exhaustive spatial and visual recording of the Quadriporticus, a 21st century complement to a 19th century triumph of effort and foresight. What’s more, photogrammetry can also help us preserve the now 134 year old cork model of Pompeii as well (Fig. 2).

Fig 2 Plastico 1879 in PhotoScanFigure 2

A hallmark of the PQP is our paperless approach (see Paperless Archaeology blog by John Wallrodt), for which we rely heavily on the iPad and a few key apps. At the same time that the iPad2 was released with a HD camera, we began a collaboration with AutoDesk Labs on their beta Project Photofly with the hope that that some basic photogrammetry might soon be possible in the field. Unfortunately, the iPad camera would not be suitable for archaeological photography until (at least) its third generation and Project Photofly, which developed into AutoDesk’s 123D Catch products (including an iPad app), required a strong internet connection to upload the necessary imagery and to download the results. The ease of making a fly-through animations when the model is complete (e.g., our Room 7, Room 40, and Room 40 with mesh view), however, remains a strength of 123D Catch. Because of the difficulty of access to an internet connection in the field, in 2012 the PQP turned to Agisoft’s PhotoScan Professional software. The software is powerful and, for the most part, intuitively designed for ease of use by non-specialists and students who are encountering the process and the program for the first time. Additionally, complex subjects can be shot as component parts (called a Chunk in PhotoScan), modeled individually, and then these parts can be themselves aligned as a complete and complex whole. 123D Catch cannot offer this option and suggests that one use another modeling project, such as AutoDesk’s own Maya. The power and ease of an out-of-the-box solution like PhotoScan, however, comes with compromises. These ultimately relate to cost. First, the professional edition costs $549 for a single educational license and a whopping $3499 for a business license. Second, PhotoScan requires a minimum of 8GB of RAM, twice what the standard laptop has installed. Certainly, this is not insurmountable, but one should look to see that her computer’s RAM is expandable before installing the program. For running image sets at the highest density settings, however, 8GB of RAM is simply too few and processes will, after many hours, simply come to a disappointing halt. Also, because archaeological images sets can be enormous (ours are c. 300MB per room, with more than 70 rooms), it is tempting to store the images on an external drive. If a PhotoScan file is opened and the images are not in the same location (say you forgot to plug in the drive), the link to the data is broken and alignment and geometry processes must be rerun. Thus, it is best to have a dedicated photogrammetry computer.

Field procedures and software processes

Our process naturally follows the contours of what the PhotoScan requires and much of that process will be similar for other programs and other archaeological environments. For example, the basics rules for capturing imagery are the same and both PhotoScan and 123D Catch and each have excellent tutorial documents and videos, respectively. For our purposes and because of our working environment, we have found that taking far more photos than is recommended to be valuable. Essentially, we ‘paint’ the subject with a large number of overview photos and then ‘walk in’ to detail shots, taking one or more intermediate images between these overview images and areas of particular interest or spatial complexity. Whenever possible, it is best to run the “Align Photos” in the lowest quality to ensure that all necessary imagery has been captured. It is particularly annoying when an otherwise complete model has a significant gap and although only one more image is needed, the subject is thousands of miles away. One benefit of shooting more images than perhaps are needed is that the missing part of a model might be found in the background of images of another subject. For the same reason, we prefer to add all possible images when running the alignment procedure because doing so both shows what images could not be automatically aligned (“NA” will appear after the file name in the image list) and what coverage the beyond the subject was also captured (Fig. 3). Such overlap is of particular importance for aligning individual models of rooms or areas since each is a small component of the Quadriporticus and will eventually all be combined into a full model of the entire building.

Fig 3 AlignedPhotos OverviewPixels NA imgFigure 3

Fig 4 BuiltGeometry pixwl clip majorFigure 4

Having all of these extraneously matched points, however, is not always useful for the next step in the process: building the model’s geometry. Therefore, we use the cropping tool to delete these pixels before running the “Build Geometry” process for two reasons (Fig. 4). The first reason is simply to reduce processing time. The second reason is that deleting these pixels is far easier than deleting the faces that result from the build geometry process. Trimming these faces is difficult enough because of their irregular triangular shapes, but it becomes especially challenging because the selection tool captures everything in three dimensions within the area selected. Thus, not only the part one wants to remove is selected for deletion, but also everything behind it (Fig. 5). This is can be a useful point to remember because, despite how one crops pixels before building geometry, PhotoScan will sometimes close areas, such as doorways, windows, or absent ceilings, that are open in the real world. Deleting these faces therefore becomes a necessary task in realizing an accurate model of an archaeological subject, particularly architectural subjects. The final process to run in PhotoScan is to build the texture map for the model from the images used.

Fig 5 BuiltGeometry texturedFigure 5

For complex subjects like the (at least) 96 rooms of the Quadriporticus, the individual models can and must be combined by the “align chunks” procedure. Depending on the imagery available and the degree to which it overlaps, this alignment process can be done automatically by the program, or, as in our case require the manual matching of points (See Olson et al., 2013, 254, 257).

Problems and Pitfalls

The primary problem of using photogrammetry in archaeological contexts, and one that is compounded in later procedures, is the difficulty of capturing the subjects with sufficient coverage, detail, and/or distinction. In many cases, it is impractical or even impossible to take a picture of every part of a subject or from all the angles the program might require. In the Quadriporticus, we encountered this problem in several ways. Sometimes we couldn’t get far enough away from a wall to get good overview coverage, at other times we couldn’t get close enough to get clear details, and some subjects were either partially or even nearly completely obscured. The design and the scale of the building itself became an issue. For example, because the columns and much of the façades’ masonry construction technique were so similar, the program had difficulty aligning these images and in the resulting model a wall would appear in the middle of a room and at an odd angle to the rest of the walls. Additionally, because of the Quadriporticus’ multiple stories, when we could not get high enough to see the tops of column capitals or close enough to a three story wall. This meant that the upper portions of the building were only captured from a distance or from below, at a sharp angle.

Fig 7 Quad light conditions IMG 4804Figure 6

Light conditions are a perennial concern in archaeological photography and this is true for photogrammetry capture as well. In the example just discussed of the high angle photos, the sun was often an issue as the sky was always significantly brighter than the wall. Many walls of the Quadriporticus (save on those rarest of Campanian summer days – overcast, but not raining) never have full sun or full shade (Fig. 6). Inconsistent lighting is a problem not only for modeling a particular wall or even room, but also for integrating that wall or room into the complete model because at different times of day (and days of the year) the shadows cast by the architecture can be radically different. For this reason, as often as possible, we took our important photogrammetry photos at the same time each day, between noon and 1PM (contrast with decision by Olson 2013, 252, 259). We chose this hour because the shadows were shortest even though the sun was brightest and the contrast between light and shadow strongest. With much of the southern portico completely or partially reconstructed, we also faced the opposite problem: very dark, fully enclosed rooms lit only by a small window in the door or a fluorescent overhead light. Since the ambient light from the window was insufficient to provide any detail, we chose to use the overhead lights, which meant we could not capture most of these rooms’ ceilings for reconstruction.

Finally, in a building with as many visitors as the Quadripoticus has on a summer day, keeping the near background of our imagery consistent was a constant challenge. Keeping the distant background free of tourists or PQP team members was impossible. We found two solutions to this concern: 1. cropping (in Photoshop prior to adding image) or masking (in PhotoScan prior to aligning) the images to exclude extraneous features, which can give the program less to match on symmetrical objects, such as flutted columns, or 2. patience. The later, though onerous while in the moment, is far more efficient compared to masking or cropping dozens of images.

Benefits of Photogrammetry

The comparatively low cost and little training required of photogrammetry make it worthy of consideration for any archaeological investigation and an essential tool for recording a structure as large and complex as the Quadriporticus. In fact, all of our costs to use photogrammetry to record the entire building are still less than 10% of the lowest quote we received for an equivalent level of coverage using a laser scanner.

Beyond the practical aspects of recordation, there are several benefits that photogrammetic models offer to archaeological analysis and interpretation. The first is perhaps so simple as to be undervalued: in a textured model one can examine dozens or even scores of images of one’s object of interest simultaneously. Moreover, one can do this in the most intuitive of manners, by simply rotating the view like one would turn her head or body. To appreciate the value of interacting with one’s data in such a manner of organization, compare it to browsing the same image set in a folder, viewing each those images individually, and opening multiple windows (each reducing screen ‘real-estate’) to see adjacent scenes. Of far greater importance is the ability of photogrammetic models to achieve angles of viewing impossible in reality. In these virtual environments, one can – in minutes – effectively float high above or stand inside solid rock. In the Quadriporticus, the best example comes from Room 40, the only place where the extrados of a large sewer that served a large part of Pompeii (Poehler 2012, 110-11; Poehler and Ellis 2012, 9-10), still exists within the Quadriporticus. The digital reconstruction allows us to see through walls, examine the sewer’s profile, consider how much of it supports the western terrace wall, and compare that profile to other known sections of the same sewer.

Concluding remarks

At the moment of writing, laser scanning has made the total station practically obsolete for capturing data sufficient to model complex archaeological architectures. What once took the Anglo-American Project in Pompeii and the Pompeii Forum Project several years to make only 3D wire frame models, as revolutionary as they were, can now be done in a matter of weeks. Photogrammetry is also on the cusp of eclipsing the laser scanner, especially for many common recording tasks. I do not expect to see another major laser scanning campaign in Pompeii like those experiments of the last decade (Balzani et al., 2004; Cyark; Hanghai, Hori, and Ajioka 299; Hori et al., 2007). Photogrammetry, in my (admittedly lagging) opinion, is the first step in a revolution for archaeological recordation in which new techniques will offer new levels of efficiency as well as a visual and dimensional comprehensiveness to permit new forms of analysis and interpretation. Calculation of volumes – of soil excavated for normalizing ceramic assemblages or sections of masonry for estimating the materials used in their creation (e.g., Delaine 1997) – being only one of the more obvious advances. The future will continue to experiment with both large- and micro-scale uses for recording, modeling, and presenting archaeological materials through photogrammetry. For example, features recovered during excavation can be extracted from individual descriptive models (i.e., those intended to replicate drawing of stratigraphic units) and recombined with related features to better illustrate and therefore test phasing hypotheses. Such work is already being done at Gabii as reported in this blog series. Additionally, we have attempted (and thus far failed) to capture and model graffiti from walls at Pompeii, though others have succeeded on ceramics (Montani et al. 2012). The ease of creating textured, 3D images of archaeological material make the use of photogrammetry as a presentation tool more of its most potent expressions. Thus, one might photograph objects now in museums to reconstruct complete funerary assemblages and recombine them with a model of the tomb itself. Similarly, one might also use image masks and markers on pictures of frescos and mosaics now housed in museums to model the decorative as well as the spatial environment of a place by attaching those frescos and mosaics to photogrammetric models of the bare but extant masonry walls. Such reconstructive efforts are already being done for classical sculpture.

I hope that this report of our work is a modest contribution to the conversations about the place, the best practices, and the future of photogrammetry in archaeological environments.

Ed. For more on this project and photogrammetry check out this sweet video and follow him on his blog.

Bibliography

Adam, J.-P. and M. Frizot 1983. Dégradation et restoration de l’architecture pompéienne (Paris)

Balzani M., N. Santouoli, A. Grieco, and N. Zaltron 2005. “Laser Scanner 3D Survey in Archaeological Field: the Forum of Pompeii,” International Conference on Remote Sensing Archaeology Beijing, October 18-21, 2004, 169–175. http://www.pompeiana.org/research/22-Balzani_Santopuoli.pdf

Cyark Website: http://archive.cyark.org/pompeii-intro

Delaine, J. 1997. The baths of Caracalla : a study in the design, construction, and economics of large-scale building projects in imperial Rome. Journal of Roman Archaeology, Supplement 25

Hanghai, A., Y. Hori, and O. Ajioka 2009. “Laser Scanning of Streets in Pompeii,” Proceedings of the 22nd CIPA Symposium, October 11-15, 2009, Kyoto, Japan. http://cipa.icomos.org/fileadmin/template/doc/KYOTO/166.pdf

Hori, Y., O. Ajioka, and A. Hangai 2007. “Laser Scanning in Pompeian City wall. A comparative study of accuracy of the drawings from the 1930s to 1940s,” Proceedings of 3D-Arch 2007: 3D Virtual Reconstruction and Visualization of Complex Architectures. http://www.isprs.org/proceedings/XXXVI/5-W47

Montani, I., E. Sapin, R. Sylvestre, and R. Marquis 2012. “Analysis of Roman Pottery Graffiti by High Resolution Capture and 3D Laser Profilometry,” Journal of Archaeological Science 39, 3349 – 3353.

Olson, B., R. Placchetti, J. Quartermaine, and A. Killebrew 2013. “The Tel Akko Total Archaeology Project (Akko, Israel): Assessing the suitability of multi-scale 3D field recording in archaeology,” Journal of Field Archaeology 38.3, 244 – 262.

Poehler, E. 2012. “The Drainage System at Pompeii: Mechanisms, Operation, and Design,” Journal of Roman Archaeology 25, 95 – 120.

Poehler, E. and S. Ellis 2012. “The 2011 Season of the Pompeii Quadriporticus Project: The Southwestern, Southern, Southeastern and Northern Sides.,”Fasti On Line Documents& Research 249, 1 – 12. http://www.fastionline.org/docs/FOLDER-it-2012-249.pdf

World Heritage Centre/ICOMOS report, 7-10 Janurary 2013.

Wallrodt, John. Paperless Archaeology Blog. http://paperlessarchaeology.com/

3D laser scanning within Skoteino Cave, Crete, Greece

This is the sixth in a series of posts exploring 3D modeling in Mediterranean and European archaeology. For more on this project click here. We hope these papers will start a discussion either in the comments of the blog or on Twitter using the #3DMedArch hashtag.

Loeta Tyree, American School of Classical Studies, Athens, Greece

3DThrusday

Laser scanning within Skoteino Cave (Dark Cave in Greek) in north Central Crete, Greece was accomplished following a three year project to image this subterranean network. The cave is of interest because of its long history of anthropogenic use since the Bronze Age that includes its function as a Minoan ritual site in the Middle Minoan III-LM IIIB period (ca. 1450-1200 B.C.) and, again in Roman times and later (Tyree et al. 2005-2006). To better understand the relationship between the areas of ancient activity, and realizing the deficiencies of existing cave maps created by the tape and compass technique, a survey team under the direction of Loeta Tyree and Athanasia Kanta engaged in a project to map the interior of the cave using more accurate digital techniques.

In 2005-2007, the survey team (lead by Antonia Stamos and Jon Frey) mapped the cave using conventional surveying methods, a TopCon GTS-303D total station and Recon data collector. The survey required well over 500 man-hours to map the floor of the cave to its farthest and deepest point, 207 m from the mouth of the cave and 70 m below the overlying ground surface. While this EDM total station technique offered an accurate representation of the cave floor including the areas of ancient and later use (Tyree et al. 2011), this technique (using a reflector) did not allow mapping of the entire cave morphology, particularly the walls and ceiling as well as most of the speleothems. As a result, this mapping technique did not accurately represent the spatial relationships essential for a clearer understanding of the cave setting for ancient and modern ritual or other use.

Consequently, the survey team turned to three-dimensional laser (point cloud) scanning for mapping the entire Skoteino cave system, from floor to ceiling. In 2009, the team, lead by Jon Frey and Antonia Stamos, mapped the entire cave and all its features using a Riegl LMS-Z420i laser scanner with a digital camera (a Nikon D-100 camera with a Nikor 14 mm lens) mounted on top of the laser scanner. Our survey was the first to use this technique to map a cave in Crete and only the second such to map such a complex subterranean archaeological site in Greece (Frey et al. 2009; Tyree et al. submitted). In four days, the team was able to map the entire cave system except the two very deepest and/or smallest areas where it was too cumbersome to manoeuvre the equipment on the slippery, uneven cave floor.

Presently, our team is still coping with the amount of data collected by our 2009 scan of the cave. Processing such an enormous ëcloudí of data has proven to be a challenge. Once we are able to produce a 3D model, we will face the next hurdle of presenting such a model in a format that can be recognized by academics and publishers. Our eventual aim is to integrate representative artifacts of cave use diachronically in their approximate find spot within the cave. The cave and artifacts from Prof. Costis Davarasí 1962 excavation of the cave are being prepared for publication by L. Tyree, A. Kanta, and C. Davaras.

In addition to laser mapping Skoteino Cave, geologist Floyd McCoy conducted a geological survey of the cave in order to understand the origin of the cave system. Measurement of cave atmospheric conditions to determine the possible influence of environmental conditions on anthropogenic use of the cave in antiquity (McCoy et al. submitted) ñ how long could such a cave be occupied before people became uncomfortable or possibly were asphyxiated by excess CO2 build up? The atmospheric measurements within the cave included temperature, relative humidity, light levels, carbon dioxide (CO2) concentrations, and air flow, all of which provide clues for extrapolation to possible conditions in the past. In addition, these measurements also focused on the fact that the internal carbonate geochemical system had changed to disallow deposition of secondary carbonates ñ why and when?

References:

Frey, J., A. Stamos, and L. Tyree. 2009. Shooting Blind: Three Approaches to Mapping Skoteino Cave, (abst.) 110th Annual Meeting, Archaeological Institute of America, Philadelphia. http://aia.archaeological.org/webinfo.php?page=10248&searchtype=abstract&ytable=2009&sessionid=2I&paperid=1600 (last accessed June 17, 2013).

McCoy, F., L. Tyree, A. Stamos, and J. Frey. Submitted. “Geology and Atmospheric Environmental Conditions at Skoteino Cave, Crete (Greece): Inferences for Cave Origin and Use in Antiquity,” Geoarchaeology.

Tyree, L., F. W. McCoy, A. Kanta, D. Sphakianakis, A. Stamos, K. Aretaki, and E. Kamilaki. 2005/2006. “Inferences for Use of Skoteino Cave during the Bronze Age and Later Based on a Speleological and Environmental Study at Skoteino Cave, Crete,” Aegean Archaeology 8 (2009): 51-63.

Tyree, L., D. Sphakianakis, A. Stamos, J. Frey, M. Belidis, and S. Kamnakis. 2011. “Speleography of Skoteino: Natural relief formations of the Caveís Interior, with Special Reference to Late Bronze Age Ritual Activity,” in Proceedings of the Tenth Cretological Congress, Literary Society, Chrysostomos, Chania A3: 717-732.

Tyree, L., F. McCoy, J. Frey, and A. Stamos. In press. “Three dimensional imaging of Skoteino Cave, Crete, Greece: Successes and Difficulties,” Journal of Field Archaeology.

Closing Gaps with Low-Cost 3D

This is the fifth in a series of posts exploring 3D modeling in Mediterranean and European archaeology. For more on this project click here. We hope these papers will start a discussion either in the comments of the blog or on Twitter using the #3DMedArch hashtag.

Sebastian Heath, Clinical Assistant Professor of Ancient Studies, Institute for the Study of the Ancient World, New York University

I start with a personal statement: I use 3D-tools because I want to bridge the gap between my work in the field – which is mainly with Roman objects, particularly ceramics – and anyone who might be interested in my efforts. To put that another way, I am able to experience objects and sites directly and I want to share the best approximation of my own access with others. “Access” is the key word here. For me, that’s what 3D modeling is all about.

3DThrusday

Optimism and Context

I’ll also begin by saying I am an optimist and think that the recent drop in the cost of generating models and the current opportunities for free distribution of those models mean that change is in the air. Of course, 3D technologies have been available for many years so it’s important to stress that there are pioneering archaeologists who dove in well before I did. And I note that they’ve done so in ways that have made substantive contributions to our understanding of major issues in Mediterranean archaeology. The Stanford Digital Forma Urbis Romae Project (Levoy and Trimble n.d.) as well as Rome Reborn (Frischer 2013) obviously merit mention here; as does Philip Sapirstein’s (2010-11) ACLS-funded online publication of 3D models from Mons Repos at Corfu. This project is distinguished by making its data available for download under a Creative Commons license. And I also briefly note work in Emerita Augusta, modern Merida in Spain, that has helped confirm and improve the re-assembly of non-joining statue fragments from the so-called “Marble Forum” in the heart of the Roman colony into a convincing Aeneas, Anchises, Ascanius group (Mercan et al. 2011). These models give vivid context to A. Jiménez’s more theoretical discussion of “mimesis” in Roman Hispania, in which that group receives considerable attention (Jiménez 2010).

Longer-term History

But having noted pre-existing work, I think it’s worth recognizing that in the history of technology, origins and early efforts are not inherently more interesting than phases of rapid adoption. As Olson and Placchetti (2013) describe, new tools are making it easier for more archaeologists to use 3D techniques. To offer a personal perspective, my own first attempts at making models using photo-based reconstruction were entirely the result of recognizing in the fall of 2012 that costs had become low, that ease of use had improved, and that distribution was possible using well-known standards (as in, “No Plug-ins!”). These three factors in combination meant there was no longer good reason not to integrate 3d into my own work as an archaeologist. And I should emphasize that it’s been enjoyable to follow colleagues on Twitter who have come to the same conclusion. Again, change is in the air.

Figure1Figure 1

But before showing the current state of my efforts, I would like to establish a long-term historical, or perhaps historiographic, perspective. Figure 1 shows Plate 34 from the report on the 1881 American excavations at Assos (Lawton and Diller 1882), the text of which is available for download from the Hathi Trust Digital Library. The dominant mode of representation of this Roman sarchophagus is linear, but shadow is used to bring out the relatively deep relief of the bucrania and the drooping garlands. Such shadows are a convention that has fallen out of favor in contemporary technical illustration. The same is true for the female figure seated at the right of the sarcophagus. There is much to say about her, and she’s an evocative intermediary between the object being represented and viewers of this image. To the extent that there is tension between the precise metric scale below the sarcophagus and our female guide, the “clinical” won that tug-of-war with the “perceptual.” Meaning that in more modern illustration such human figures are part of recreations and are less welcome in technical and measured drawings.

Figure2Figure 2

Figure3

Figure 3

This trend from realism to abstraction is particularly apparent in current best practices for the illustration of wheel-made ceramic vessels. Figure 2 shows a drawing by Piet de Jong of a late Roman table vessel (an African Red-Slip Hayes form 97 of the sixth century A.D. to be more specific) as viewable on the website of the Athenian Agora Excavations. It is a representation that emphasises shape, depth, surface treatment and color all in one image. As a recent catalog of de Jong’s Agora illustrations noted of this drawing, “His watercolor is a peek into all aspects of the pot.” (Papadopoulos 2006, no. 129). Now compare it with figure 3, a profile drawing of an ARS form 87 found at Troy (Heath and Tekkok n.d.: P18.0093:1). Such profile drawings are the “gold standard” of modern ceramic publication. When well-executed, they permit a ceramicist to confidently compare an example in-hand to a drawing of a potentially similar piece. That’s an important step in the full analysis of a ceramic assemblage. But it is also important to note that there is nothing “realistic” about profile drawings. They utilize a code of sorts that requires considerable mental processing to move from their abstract representation to a sense of the real vessel.

The above was a very long way of saying that we are catching up with – and going beyond – where we’ve always wanted to be. That is another “gap” potentially closed.

Models at Kenchreai

As for my own work, three models will show that I’m in the early stages of closing gaps between what I’m doing in the field and my stated goal of sharing as much as I can. Figures 4, 5, 6 are screen captures that link to the site “p3d.in”, one of a few options for sharing 3D models that are currently available. All of them come from my work as part of the American Excavations at Kenchreai, which operates with a permit from the Greek Ministry of Culture and under the auspices of the American School of Classical Studies at Athens. I am very grateful to the project director Joseph Rife of Vanderbilt University for the opportunity to include these models in this discussion.

Figure4Figure 4

The first model (figure 4) is of a Late Roman lamp (KE 235). A brief description of creating it is online via a guest post I contributed to John Wallrodt’s Paperless Archaeology blog (Heath 2013). Its original inventory information is available as part of the Kenchreai Archaeological Archive here.

Figure5Figure 5

My second model (figure 5) is a statue base with figure preserved only to just above the ankles (KE 1221). It is a beautiful piece and I hope that even this preliminary model captures some its interest. Its preliminary documentation is also available online here.

Figure6Figure 6

The third model (figure 6) is of a stretch of marble stylobate from the so-called “Aphrodiseion” at Kenchreai (Scranton et al. 1978, p. 79).

As noted, the three images above are screen captures from the model sharing website P3D.in and readers can click on the associated links to go directly to the relevant page there. Assuming you are using a compatible browser – Safari, Chrome, or FireFox, but not Internet Explorer – it should be possible to rotate and zoom in on the models.

That access is the illustration of my opening point and the current fulfillment of the title of this post. By which I mean that even within the context of a relatively small project that needs to be careful with its resources, the creation of 3D models is possible. And not just creation, but sharing as well. That is “gap” closing.

Figure7Figure 7

A next step is re-use. I illustrate that by way of a fanciful combination of scaled versions of my three example models (figure 7). The dataset is too big to load usefully into p3d.in so the image is static, but I hope that it hints at a future in which ready availability of 3D data closes gaps between categories of object, their original contexts and the archaeological (or other) sub-disciplines that study them.

One final point: it should be clear that this is all work in progress. The models are far from perfect and my colleagues at Kenchreai and I are in the early stages of thinking about how new opportunities can contribute to our research design. One sign that the project considers these models “final” will be that end users can download them and do their own mixing, or to put that differently, their own research. That won’t be quite the same as being on site or handling the lamp and statue in-person. But it should be clear that I am optimistic that this access will be close enough to enable new “peeks” at aspects of the material that were previously available only to a very few.

Works Cited

Clarke, J. T., Lawton, W. C., and Diller, J. S. (1882). Report on the investigations at Assos, 1881. Boston: A. Williams.

Frischer, B. (2013). Rome Reborn. <http://romereborn.frischerconsulting.com>.

Heath, S. (2013-08-14). Two Kenchreai 3D models. Paperless Archaeology. <http://paperlessarchaeology.com/2013/08/14/two-kenchreai-3d-models/>.

Heath, S. and Tekkök B. (n.d.). African Red Slip. In Greek, Roman and Byzantine Pottery at Ilion. <http://classics.uc.edu/troy/grbpottery/html/ars.html>.

Jiménez, A. (2010). Reproducing Difference: Mimesis and Colonialism in Roman Hispania. In B. Knapp and P. van Dommelen (Eds.), Material Connections: Mobility, Materiality and Mediterranean Identities (pp. 38-63). Abingdon, Oxon: Routledge.

Levoy, M. and Trimble, J. (n.d.). Stanford Digital Forma Urbis Romae Project. <http://formaurbis.stanford.edu>.

Merchán, P., S. Salamanca, and A. Adán (2011). Restitution of Sculptural Groups Using 3D Scanners. Sensors 11 (9), 8497-8518.

Olson, B. and R. Placchetti (2013-09-13). A Discussion of the Analytical Benefits of Image-Based 3D Modeling in Archaeology. The Archaeology of the Mediterranean World. <https://mediterraneanworld.wordpress.com/2013/09/12/a-discussion-of-the-analytical-benefits-of-image-based-3d-modeling-in-archaeology/>.

Papadopoulos, J. K., Camp, J. M. K., & De, J. P. (2007). The art of antiquity: Piet de Jong and the Athenian Agora. Princeton, NJ: American School of Classical Studies at Athens.

Sapirstein, P. (2010-11). The Archaic Sanctuary of Mons Repos at Corfu. <http://sites.museum.upenn.edu/monrepos/>.

Scranton, R. L., Shaw, J. W., and Ibrahim, L. (1978). Kenchreai Eastern Port of Corinth: I, Topography and Architecture. Leiden: Brill.

Bring in the Drones: 3D Modeling Using Aerial Imagery at Archaeological Excavations

This is the fourth in a series of posts exploring 3D modeling in Mediterranean and European archaeology. For more on this project click here. We hope these papers will start a discussion either in the comments of the blog or on Twitter using the #3DMedArch hashtag.

Ryan Baker, B.A. Student in Classical Archaeology. University of Texas. Co-Founder ArchAerial LLC.

For every joke I endured this summer about technology from the Starship Enterprise coming to the field of archaeology, a real conversation followed about the future of the discipline in terms of digital representations of an excavation.

3DThrusday

I’m an undergraduate student finishing my B.A. in Classical Archaeology at the University of Texas at Austin, and last fall I started a small business called Arch Aerial LLC that set out to create easy to use aerial photography platforms with autopilot capability in the form of multi-rotor helicopters and small fixed-wing UAV’s.  Initially, we were only looking to work with universities and research institutions working in the field of archaeology, but our project has evolved into something with the potential to increase efficiency in any field or industry with a spatial component.  

Atlas 1 Quad Rotor

This summer, we field-tested our new prototype at over 10 excavations within the Programme for Belize Archaeological Project, the Swedish Institute in Rome’s San Giovenale Tomb Survey in Blera, and the Poggio Civitate Archaeological Project in Murlo.  We conducted a number of different surveys over the course of the summer, often depending upon the environment and research interests of the project directors.  Our teams directed large-scale aerial survey, videography, and (most importantly for this article) a great deal of 3D modeling in Agisoft Photoscan using images taken from the air by our multi-rotor aircraft.

Using these small multi-rotors we produced 3D models of the trenches at closing, and in some cases, at the beginning of each day of excavation to show the progress of the trenches as the season progressed. For example at Poggio Civitate, using my MacBook and a minimal number of photos, I built a model of the trench each morning in relatively real-time (within 20 minutes of capturing the photos) and gave the site director a real-time view of the state of excavation. This is a task that could be completed by any member of an excavation. At the beginning of each day work day, or even as each locus of a trench closes, a staff member could image the site in a matter of minutes and create 3D representations of the excavation for internal research or later publication. This method is not limited to only small features: in addition to areas of open excavation, we captured the imagery to build a 3D model of the entire hill at Poggio Civitate, and rendered models of ball courts and temples from multiple sites within the Programme for Belize Archaeological Project.

Ball Court  Unexcavated 3D Model3D model of the ball court

Adverse conditions were an environmental trait we sought out this summer. Within the Rio Bravo Conservation and Management area, we operated under the rainforest canopy for nearly the entire season while surveying excavation at the Programme for Belize Archaeological Project. Similar to our procedure at Poggio Civitate, we were able to take photos and build our model on site in an extremely short amount of time. Below is a 3D model of excavation on Medicinal Trail by Dr. David Hyde, which we built in Agisoft using imagery taken by one of our quad-copters.

Medicinal Trail 3D Model Screenshot  2Medicinal Trail 3D Model

Many of the parts for our new multi-rotor are prototyped and made in house using our 3D printers. Although this is certainly useful for manufacturing parts, it also gives us the opportunity to take the next step past just rendering 3D models in Agisoft. Using 3D .OBJ files we’ve built of artifacts, trenches, and the entire hill at Poggio Civitate, we can print small-scale versions of the models in ABS plastic.  This has huge implications in terms of giving researchers hands on access to artifacts that might not be allowed out of a host country.  If researchers are able to 3D model artifacts that can’t leave the excavation archives, they can then print them and have to-scale models of their artifact using inexpensive materials and an easily repeatable process. We’ve decided to do just that, and upon returning to Texas our team will be printing models of artifacts and trenches for the excavations mentioned above.

Over the course of the summer I heard plenty of hokey sci-fi references, but I think it is safe to assume that 3D modeling and printing will have their place in the field of archaeology. As the cost of adopting these methods decreases (as it has with Agisoft Photoscan), it only makes sense to add another dimension to the description of archaeological excavation and it’s dissemination to the public through digital publication.

Linear B in 3D

This is the third in a series of posts exploring 3D modeling in Mediterranean and European archaeology. For more on this project click here. We hope these papers will start a discussion either in the comments of the blog or on Twitter using the #3DMedArch hashtag.

Dimitri Nakassis, Associate Professor, University of Toronto

Bill’s invitation to write up some thoughts on 3D modeling in Mediterranean archaeology came at a welcome time for me, as I had just co-directed the first season of a project imaging the Linear B tablets from the “Palace of Nestor.” The project makes use of two 3D technologies: Reflectance Transformation Imaging (RTI) and 3D scanning using a Breuckmann smartSCAN 3D white light scanner.

I should probably take a step back and explain the project a little. The project is co-directed by myself and Kevin Pluta; also participating are James Newhard, who in handling the informatics, and Benjamin Rennison, who was running the white light scanner. We were assisted by Jami Baxley, an undergraduate student at the College of Charleston. This project is an extension of a much longer-running project to publish the Linear B tablets from the “Palace of Nestor.” This material was assigned to Emmett L. Bennett, Jr. by the excavator of the palace, Carl Blegen, and in the first volume in the Palace of Nestor series, Blegen announced that the publication of the tablets would constitute the fourth volume. That volume has not yet materialized, in large part because much work remained to be done — for years the editors of the volume have been making joins and revising transliterations. Kevin and I are directing the resumption of work on the project.

Corpora of Linear B texts follow a time-tested formula that has hardly changed since the beginning of Linear B studies. For each text, the reader is provided with a line drawing, a photograph, and (post-decipherment) a transcription:

Figure 1

Caption: the line drawing and photo of a tablet from Scripta Minoa II

This formula is useful, but of course it is somewhat limited by the print medium for which it was designed. Ultimately, the problem is that the standard corpus is a record of how the editors see the tablet. It relies on editorial authority. The line drawing is of course an interpretation of what the editor sees, not an objective record of what is actually present. The photograph is arguably an objective record, but rarely is it high-resolution enough as printed for a scholar to use to overturn an editorial reading.

A 2007 article written by Yves Duhoux illustrates some of the problems of traditional corpora. Duhoux argued for a new reading of a fairly famous tablet, Knossos F 51. Duhoux was able to show that previous editors had seen a vertical line that was actually an accidental scratch on the tablet’s surface. In order to clinch his argument, Duhoux reproduced a high-resolution image of the tablet and another image in which he zoomed in on the sign in question. This latter image was about 1″ x 1″, about 16 times larger than its size as printed in the Knossian corpus. The sign had been incorrectly identified more than once by the most experienced and careful editors in Mycenaean studies, and the word to which it belonged become the center of a debate about Mycenaean religion sparked by the discovery of Linear B tablets from Thebes in the mid-1990s. In this case, then, the reading of a single sign had enormous scholarly implications.

When we began to think about how we wanted to document the Pylos texts, these issues were front and center for us, and we started to look at what other people were doing with similar documents. I was kindly shown the operations at the Oriental Institute at the University of Chicago, which was using RTI to document tablets from the Fortification Archive from Persepolis. I also met with Yannis Galanakis at the Ashmolean, who was already arranging for a team from Southampton to use RTI to document the handful of Knossos tablets in their collection. That work has now been published online.

This past summer (2013), then, we began our first season of documenting the Linear B tablets from Pylos using two new techniques, RTI and 3D scanning. We see RTI as a replacement for traditional photography. Briefly, the way it works is that we take 54 images of each inscribed surface of an artifact, mostly clay tablets but also clay sealings and labels. For each photo, the artifact and the camera are static, with the camera pointed straight down onto the surface of the tablet. What changes is the position of the flash, which we move manually. We photograph the tablet from 9 positions on the horizontal plane, and for each position we take 6 pictures from different angles, from 15 degrees to 65 degrees. The process of taking these photographs takes less than 2 minutes.

Figure 2Dimitri Nakassis holding the flash for RTI capture

The result is the production of a PTM (Polynomial Texture Mapping) file which records the color of each pixel as a function of the lighting conditions. (See here for a more detailed description of how RTI works). These PTM images can be manipulated in an interactive environment using several free programs, allowing the viewer to change the directionality of the light source to best illuminate the particular sign that s/he is interested in.

Unfortunately we do not have permission at this time to reproduce the images, but the PTM files made available by the Ashmolean illustrate the value of this approach. One of their tablets, KN Ra 1540, is a fairly straightforward text that is transcribed “to-sa / pa-ka-na PUG 50[“, which we could translate “so many swords: SWORD 50.” Here is a straightforward color image and its black and white counterpart (which is what we would get in a printed edition):

Figure 3Figure 4KN Ra 1540, exported from RTI viewer

Slightly odd for those familiar with the Linear B script is the sign na (immediately to the left of the sword), which is damaged by a break running vertically through it. Because pa-ka-na means “swords” (phasgana, cf. Greek φάσγανον, plural φάσγανα), we know that it must be a na, which normally looks liks this:

Figure 5

na, drawn by John Chadwick

But using the RTI viewer we can zoom in on the sign (because the images were taken with a high-resolution camera) and reproduce the effect of raking light on the tablet, producing this figure:

Figure 6KN Ra 1540 detail, exported from RTI viewer

What this shows fairly clearly is that the mark above the “na” (circled in light green-blue) is not an intentional mark inscribed by a scribe, but is rather part of the damage to the tablet. All of the other intentional marks were made when the clay was wet, and the raking light clearly shows the lip of clay around these incisions, created by the writing process. The unintentional mark shows no such lipping, and must have occurred after the clay was hard.

This isn’t a great insight; the size of the signs is such that it’s likely that any mark above them isn’t intentional (note that the horizontal stroke from the <i>na</i> is at the same position as the height of the sign to the left, a <ka>). But such observations are important, as Duhoux’s article shows, and these RTI files allow researchers with access to the internet to examine the tablets at a level of resolution that approaches autopsy.

For us, this is the main take away for the use of RTI. It’s not just a fancy photograph, but it allows us to redistribute the authority of the editor to all interested and qualified users. This doesn’t mean that traditional standard corpora are useless, of course. Sometimes one wants to consult the texts through the editor’s expert eye. On the other hand, for those who are interested in editorial decisions, RTI gives them the opportunity to examine the tablets at a level of detail that would allow them to develop their own readings. At this point, I’m not convinced that our PTMs are superior to autopsy, but the advantage of the PTM files is of course that unlike the tablets, they are digital files that can be readily shared. This suggests a second advantage of RTI, which is the conservation of the Linear B tablets. The less the tablets need to be handled, the better it is for their management.

This addresses Bill’s first and fourth prompts: RTI, I’d argue, is qualitatively different from photography, at least in the case of this type of inscribed document. A photograph represents a tablet, but doesn’t even approximate autopsy. RTI has the potential to radically change the field from one in which editorial authority rules supreme and is the foundation of all subsequent scholarly practice, into one in which editorial authority is dispersed and all experts have the ability to read the texts for themselves.

Figure 7Ben Rennison scans a Linear B tablet using the Breuckmann smartSCAN 3D white light scanner

The other method we used was 3D scanning using a white light scanner, generously loaned to us by Breuckmann. I’m going to talk about it less, in part to save space and in part because I was less active in this aspect of the project. This scanner works by projecting a sequence of fringe patterns (black and white lines) onto the tablet, while two cameras capture the projected pattern in full color. We also had a turntable that allowed us to turn the tablet without moving it by hand. This scanner provided us with high-resolution three dimensional models of the tablets in color. We wanted to use the 3D scanner in conjunction with RTI because unlike past editions, we wanted to record the tablets as three-dimensional objects. The tendency in most textual corpora is to flatten the artifacts and to reduce them to writing. This is, of course, a convenience that is made necessary by the limitations of the printed corpus. Kevin Pluta and I, both of whom had studied the tablets for 15 years or more, were constantly astounded by the variety of shapes and surfaces that the tablets came in, which demonstrates the extent to which our scholarly tools suppress the physical form of the inscriptions. We also wanted to document and understand the manufacture of the tablets and the physical shape of the tablets, including the non-inscribed surfaces (most tablets are inscribed on only one side; fewer are inscribed on both sides; a very few have writing on the edges). The tablets are, after all, artifacts, yet very rarely have they been treated as such. Cross-sections of Linear B tablets, for instance, are not drawn.

Between these two methods, we’re hoping to provide scholars with a digital corpus of the administrative texts from Pylos (once we get permission) with PTM files and 3D models, along with other data and metadata (like precise archaeological findspots). This corpus will provide much more than any print edition could ever hope to. RTI and 3D scanning will provide the user with highly accurate renditions of the color, shape, topography, and texture of each and every administrative document from Pylos. There are two closely-related advantages that we see to this digital imaging. First, we anticipate an improvement in the conservation and archiving of the physical artifacts, since the availability of high-resolution images in two and three dimensions will reduce the need for their study and handling. Second, a digital edition provides users with the ability to work interactively with the administrative documents in a digital environment. The resolution of the imaging is such that it even permits users to propose new readings and joins. This allocation of high-quality primary data to scholarly experts represents an exciting development. Far from being merely an enhancement of standard methods of illustration, these imaging techniques have the potential to transform the field by distributing control of the primary data to all qualified experts.

Three Dimensional Field Recording in Archaeology: An Example from Gabii

This is the first in a series of posts exploring 3D modeling in Mediterranean and European archaeology. For more on this project click here. We hope these papers will start a discussion either in the comments of the blog or on Twitter using the #3DMedArch hashtag.

Rachel Opitz, Post-Doctoral Fellow
Center for Advanced Spatial Technologies (CAST) & Department of Anthropology
University of Arkansas

3DThrusday

In asking for contributions to this series of posts reflecting on 3D modeling in archaeology, Bill Caraher posed a series of questions, one of which was,

“What is the future of 3D modeling in archaeology? At present, the 3D image is useful for illustrating artifacts and – in some cases – presenting archaeological and architectural relationships, but it has yet to prove itself as an essential basis for analysis or as a robust medium for communicating robust archaeological description. Will 3D visualization become more than just another method for providing illustrations for archaeological arguments?”

I’d very much like to answer “yes” to the question posed above. I’m going to argue that 3D modeling and visualizations can be the grounds for the re-interpretation of essential archaeological evidence, stratigraphic sequences, in a way that goes beyond just providing illustrations for arguments and conclusions drawn from other evidence. To make this argument, I’ll start by providing a bit of background about 3D field recording at Gabii – an irreverent history of our digital documentation method and how it evolved.

Here’s what happened, as I remember it. In 2009 Prof. Nicola Terrenato, in a moment of enthusiasm and with the support of the Project’s other directors, decided to open a big excavation area at Gabii. He decided that the Gabii Project should develop a field survey method that would let us work quickly, so we could make efficient progress excavating in a big urban area. This would allow us to ask and maybe answer some big questions like ‘How did the urban fabric develop, change over time, and decay at Gabii?’ In addition to a fast survey-to-GIS-to-printed plan strategy, as an experiment, we were going to try recording some of the more complex contexts using photomodeling, as we called it after the Eos PhotoModeler software. Photomodeling would allow us to rapidly produce orthophotos of complex contexts, thereby avoiding tedious stone by stone survey in the field.

Opitz Fig1All
Detailed drawing using orthophotos generated from 3D models

Luckily in 2009 we didn’t find much in the way of complex architecture or stratigraphy. We modeled a few contexts in the course of the season, and they turned out well. We were confident enough in the technique’s efficacy that when an orientalizing infant burial was uncovered on the last day on site (see Becker and Nowlin, 2011) 3D modeling was our primary means of recording the remains and we were only a little nervous. In 2010, when we started uncovering an Imperial necropolis and the remains of two houses, we used Photomodeling (more formally known as Structure From Motion -SFM- , or Image Based Modeling -IBM-, or Digital Close Range Photogrammetry -DCRP-) to record all the structural and human remains. Photomodeling swiftly, and without us really making a conscious choice about it, transitioned from being an experiment to being a key part of our recording strategy. In 2011 the scale of the excavation exploded.  We were left with a substantial backlog for model processing at the end of the field season. Disaster! Much post-season work ensued. Post-season research in 2011 led us to switch to Agisoft Photoscan for the 2012 field season. The faster processing times and ability to batch script in python helped us break the backlog in one season and get back on top of the workflow. 2012 was also the year that we introduced Unity3D on site as a tool for building and sharing more complex scenes with 3D models of multiple contexts, shown in relation to one another. 

Opitz Fig2Jessica Nowlin taking photos for 3D model creation. 

2012 was also the year that we switched to LP Archaeology’s ARK system for our descriptive data management. This was a fortuitous convergence, as having a web-based data management system meant that linking from the Unity3D content and from GIS content to database entries was fairly simple. Some 2012 post-season work was devoted to promoting ARK and Unity3D within the group as a means of distributing and presenting the models. Notably, several members of the excavation staff kindly agreed to participate in an interpretive experiment, which I discuss below. All of this was good news, because 2013 brought us the largest, most complex collection of structural remains to date. We finished the season with a small, but manageable backlog.

In short, the field recording system fundamentally works, six hundred odd individual models later. We’ve gone from SFM as an experiment to SFM as normal. I think this is one of the more important things we can say about 3D field recording at Gabii. It’s just part of the routine – a proven method.

Opitz Fig3A typical single context model viewed in plan (left) and perspective (right).

All of the excavators feel that the interpretive sketch is still essential (we agree with them) and sometimes worry that all the excitement surrounding SFM and the speed it encourages us to document at will end up de-emphasizing actually looking at the archaeology, reflecting on what you see, and interpreting it via drawing carefully and slowly. This is an important ongoing debate about field recording within the team. The technology encourages us to speed up so we can work at larger scales, important, as we’ve said, for answering large scale questions, but the archaeology in many instances demands that we slow down and think about what we’re doing. So striking the balance between speeding up where we can, and slowing down where we need to… easier said than done. It takes a lot of discipline on the part of the excavators to not drift into a false sense of security from the seeming completeness of SFM models, and end up getting sloppy on other bits of their documentation. To their credit, they’re the ones constantly on guard against letting the technology overtake careful documentation and thinking and interpretation in the field. I don’t expect this particular conversation to end any time soon, nor would I want it to end, as I think this kind of constant monitoring of the balance between speed and detail, between rapid documentation of basic data and taking the time to make thoughtful interpretations is good field archaeology.

Five years in, we’re still adapting our approach as the nature of the archaeology we are encountering changes, but for us most of the debate has moved from 3D recording as a field method to the implications of the 3D documentation for publication, communication and interpretation. I’ve taken a not inconsiderable amount of space to talk about the development of our field recording system because I think in order to talk about the question which Bill posed, about the role of 3D modeling beyond illustration, as part of analysis or as a robust communication medium, it has to be everywhere, fully integrated into the normal recording practice of an excavation. If it’s something being done experimentally, for only a few contexts, or in a limited area, if it’s not part of the excavator’s practice, then it really can’t be fully part of the interpretive stage or the communication and publication stage. Equally, it can’t just be in the hands of the project’s specialists. It has to be used by the project’s team at large (something only starting to happen for us now). The length of the narrative above reflects the incremental way in which new technologies and practices develop and become part of excavation methodology, something that happens through a sustained effort over an extended period.

We’ve just started up a new NEH funded project, Gabii Goes Digital, in which we are trying to use 3D content as more than a tool for documentation. Gabii Goes Digital focuses on developing a process for the peer reviewed publication of the kinds of digital 3D models and complex, interactive datasets that projects like ours are now producing using SFM and related 3D field recording technologies, and building a community of peer reviewers with a shared frame of reference for evaluating these publications. You can read more about the project and find some prototype examples of our 3D content here. This project is bringing us, at last, close to engaging with Bill’s question, “Will 3D visualization become more than just another method for providing illustrations for archaeological arguments? [Can 3D modeling] prove itself as an essential basis for analysis or as a robust medium for communicating robust archaeological description? ” The peer review process is designed to, among other things, help authors strengthen their argument and clarify its presentation. As researchers and academics, we’re trained to recognize good and bad writing, and to identify holes and weaknesses in a argument. We learn what makes a useful chart or illustration. But what does good, useful interactive 3D content look like? What are the qualities on which it should be assessed? To develop a framework for the critique and review of what is essentially mixed visual and written content, we have to think about the link between visualization and interpretation and ask ourselves: Is visualization illustration, or part of the interpretive process and a means of interrogating the data? This question represents, I think, the nub of Bill’s broader question about illustration, description and archaeological argument. In responding to this question, I would argue that these models should be understood in the context of the discipline of information visualization, as part of a school of visual communication and argument ranging from John Tukey’s writing on Exploratory Data Analysis (1977) through Nathan Yau’s posts on flowingdata.com.

This perspective no doubt stems from my work as an archaeologist away from the Gabii Project, in which I specialize in airborne laserscanning (ALS) applications in archaeology, a field in which information visualization and visual interpretation are viewed as fundamental parts of the research process. Consequently, I’m predisposed to think that creating and engaging with visualizations is part of the process of interpretation and understanding the physical remains ‘on the ground’ and the archaeology at hand. It’s why I take the process of publishing and critiquing the models so seriously. I’m going to lift a few paragraphs from a volume I recently co-edited with Dave Cowley (RCAHMS) about airborne laserscanning in archaeology, which I think can be transposed fairly directly onto my thinking about 3D modeling in excavation contexts.

“In particular, the last decade has seen an exponential growth in the use and awareness of ALS [substitute here 3D modeling] by archaeologists and cultural resource managers[…] The powerful images produced, all promised a brave new world. And so it is – a world of possibilities and challenges, both in ensuring appropriate, archaeologically reliable applications that inform us about the past, but also in developing practices that integrate the strengths of new possibilities in manipulation and interrogation of vast digital datasets with so-called ‘traditional’ skills of archaeological observation and interpretation “

Engagement with digital 3D data “highlight[s] the importance of combining ‘field-craft’ and observation with the powerful algorithms and visualisation techniques that dense and/or extensive 3D data demand if we are to do anything more than scratch the surface.”

“In all cases the integration of 3D data into archaeological practices promotes the use of ever more sophisticated modelling and visualisations, from the creation of virtual replicas for display in a physical or digital museum or dissemination over the internet, to virtual reality and immersive visualization projects. Throughout, while the primary aim of these products may be to communicate and engage with a wide audience, these approaches also have a vital role for the investigating archaeologist in supporting interpretation where the visualization and measurement of very small scale and subtle features is essential (e.g. tool marks or rock art), and to under-pin spatial analyses such as viewsheds and least cost-paths, and inclusion in interactive virtual reality models. Universally, it is the use of 3D data as an articulation of archaeological topography that lies at the heart of the processes.”

It was with all this very much in mind that I posed the question in a paper I gave at the 2013 Meeting of the SAA: Does working with the models actually change our interpretations of the stratigraphy and therefore of the archaeology? This question sits at the intersection of what we do in the field and what we do in publication and as critical readers, and is closely tied up with Bill’s question.

To start exploring these questions of interpretation, Marcello Mogetta (University of Michigan), Marilyn Evans (Berkeley) and Troy Samuels (University of Michigan), all members of the Gabii team, agreed to help out with an experiment. They are respectively an assistant director, area supervisor, and assistant supervisor at Gabii, and so represent different levels of experience and perspectives on the archaeology being uncovered.

I gave them all an assignment:

  • Pick a stratigraphic sequence in which you’re interested, preferably one in which you recall us having done some 3D modeling.
  • Write down in brief your interpretation of the sequence and generally how you understand it.
  • I’ll put together a model of the sequence, which we’ll go through and look at together.
  • I’ll leave the model with you. You can decide if you now want to reinterpret anything. Write down, or tell me about your re-interpretations or lack thereof and if you found the model at all useful.

Each chose a stratigraphic sequence, Troy picked a series of floor surfaces within a room in an archaic complex, Marilyn picked another series of surfaces which intersected with a tomb, while Marcello chose to look at a series of surfaces which might or might not have been part of the road which delimits the block containing the archaic compound on its eastern side. Each initially formed their interpretation using the documentation other than the 3D models.

Troy began by constructing the following stratigraphic sequence and interpretation:

SU 3163 (Truncated N-S Wall covers accumulation SU 3165 (not photo modeled)).
SU 3165 covers collapse layer 3168 (collapse of earlier wall).

This collapse layer covers two patches of one yellow floor surface (SUs 3180 and 3181) and three patches of a separate yellow floor surface (SUs 3192, 3193, 3194) identified and differentiated by proximity and color. These two floor surfaces are, potentially, separate floor preparations of the archaic compound that continues across the later drainage channel (Area D Room 2). A light brown silty layer of accumulation (3202) runs beneath the floor patches 3180, 3192, 3194, 3193 and a separate grey accumulation layer (3182) runs beneath 3181. Neither 3181 nor 3202 were photo modeled.

My general understanding of this sequence is that there are two patchy heavily disturbed levels of archaic floor surface associated with a wall. This wall collapsed (3168) and a later wall (3163) was built on top of this collapse on a different alignment using the debris.”

A screenshot of the scene put together to respond to Troy’s question.White polygons indicate the locations of the surfaces in which we were interested.

After working through the model together (to get over any hiccups with the interface) and leaving it with Troy for a while, he followed up with this set of notes:

“The 3D model itself, I think, shows some grounds for reinterpretation of the relationship I originally spelled out.

Looking at this model, it seems that these patches of floor are part of one flooring event, not two distinct surfaces as I originally wrote.
While patchy, there seems to be a level of connectivity across the whole model with the variances in presence and elevation possibly related to the destruction/collapse levels sitting on top of these layers.

This was not clear from either the interpretations on the SU sheets or from the photographs. It is easier to think of and view these isolated patches as a single floor with the model than through other means of reconstruction (drawings/photos/etc.).
I think, for this specific sequence, the ability to simultaneously view the different patches was something that the 3D model provided that, outside of a brief period pre-excavation, it was difficult to reconstruct.

Because these two patches (3180/3181 and 3192/3193/3194) were excavated on different days (probably by different students and certainly while other things were taking place) the model gave me the ability to look back and think about this corner of the Area in a more cohesive way.”

Marilyn had chosen to look at another room from the same archaic complex, further to the north. Her question was more of a general exploration, where Troy’s had been fairly specific. She was hoping to better understand a complex sequence of deposits and structures. We explored the assembled model of the room together, not coming to any immediate conclusions. We did strike upon one idea, looking at a gap in an alignment of stones interpreted as a wall in the complex. This gap, we noted, lines up nicely with the central pillar in the room. While a doorway had been identified in the northern wall of this room in the field, looking at the model suggested the idea that there might be another entrance, through the western wall. Nothing concrete, but an idea to play with and think about further during the next season of excavation. Marilyn noted that the idea of a doorway seemed increasingly satisfactory. And it’s not something we would have noticed without the freedom of movement, and that little bit of distance you can get playing with the model.


Opitz Fig5

Two walls from the sequence Marilyn wanted to study, showing the gap in the west wall.

Marcello interested himself in a later sequence, related to the establishment and life of the system of streets which structures the urban plan at Gabii from about the 5th c. B.C. He originally noted:

“Below the thick deposit of silt that obliterated the entire block corresponding to Area D (SU 3004=3049), the excavators identified a layer (SU 3053) whose limits coincided with one of the roads of the orthogonal town-plan (road 2, between Area C and D).

The excavators interpreted SU 3053, therefore, as road surface. The road surface covered a deposit (SU 3066) which filled a cut in the bedrock containing multiple burials (SU 3081; Tombs 41-42). The tomb is located immediately east of the precinct wall which delimited the archaic compound (SU 2219).

The west niche of the tomb was dug under the wall, causing its collapse at a later stage.The stratigraphy seems to provide crucial evidence to understand the sequence of occupation and general phasing of the site, showing that the creation of the orthogonal layout postdates the burials, which can be in turn connected with the abandonment of the archaic building.”

Opitz Fig6

A screenshot from the scene assembled to investigate Marcello’s question.

He had a whole series of questions about the sequence, which had emerged from previous seasons of excavation:

“Is SU 3053 really a road surface?

What is its spatial relationship (especially in terms of elevation) with the deposits that cover the rich infant burial T48, farther to the south (SU 3134=3165)?

Are these road surfaces too? Probably not, because they have a stratigraphic relationship with a series of abandonment layers (SU 3129, 3128, 3117, 3115).

But how are these abandonment layers different from SU 3053?”

After looking at the model, the initial interpretation of the stratigraphic sequence was revised. He noted:

“The model proved very useful for the interpretation of the road sequence, especially SU 3134. The limits of this SU correspond to those of road 2, as can be reconstructed on the basis of SU 3053. The SU seems to represent a leveling layer for the creation of road 2 (in fact, it seals the fill of a 500 BCE infant burial).

As a consequence, the structural feature next to it (SU 3163) may represent a retaining wall for the road, not a feature relating to the archaic compound (though perhaps it was built repurposing the collapse of the precinct wall).

In light of this, I would now suggest that SU 3128 is the original road surface
which was packed on top of the leveling layers (in fact it also includes a concentration of pebble-like stones, perhaps the glareata?). The elevations are consistent with this reconstruction.

On the other hand, I now doubt that there is a direct stratigraphic relationship between SU 3134 and SUs 3129, 3117 and 3115 (it seems to me that this depends on the fact that SU 3134 was initially considered as extending west of structure SU 3163.”

So in all three cases the interpretation of the stratigraphic sequence changed, in more or less significant ways, after incorporating the 3D models into the interpretive process. I would argue, based on this experiment, that if our understanding of stratigraphic sequences, those fundamental building blocks of the interpretation of excavation data, are being changed on the basis of working with 3D models, then we are already beyond ‘illustrations for arguments’, and I feel we can answer “yes”, 3D modeling is in the process of proving itself to be an essential basis for analysis and a robust means of archaeological communication, argument and narrative.

Interim conclusions? Methodological development is messy, and the impacts of new technologies on actual practice are usually indirect and only emerge later. The personalities involved are important, because the obstacle isn’t so much the technology itself but rather our motivation to use it and our default behaviors, the tools we reach for when sifting through archaeological evidence, and the interaction between those tools and our thought processes as researchers and readers. These ingrained practices, our field habits and our desk habits, don’t evolve quickly. We talk about 3D field recording and SFM as new technologies. The ground on 3D field recording at a large scale was broken by people like Dominic Powlesland working at West Heslerton in the early 1980s, and we’ve had large scale SFM-based recording going at Gabii for almost five years now. ‘New’ is relative. Continued reassessment of our practices is essential, as is a willingness to go out on technical and methodological limbs. 3D modeling will only get through the ‘experimental’ phase of the process whereby it becomes a tool used by the archaeological community at large for analysis and as a robust means of making an argument if we actually try and use it to do these things, publish or otherwise share the results and the process, and are willing for it to occasionally go wrong. As always, it will take time and effort for new methods to become fully integrated into our interpretive work, our writing, our reading, and our way of thinking. As we work within the Gabii and Gabii Goes Digital Projects to use 3D modeling to record and interpret excavation data, make archaeological arguments and communicate them well, and push to have all this become part of the ‘normal’ publication record, embedded in the conversational cycle of of publication and review and critique and response, I am optimistic that it will be time and effort well spent.

References

  • Becker, Jeffrey A. and Nowlin, J. (2011). Orientalizing Infant Burials from Gabii, Italy. BABESCH 86:27-39.
  • Opitz, R. (2013). Digital Transitions: Technologies for Archaeological Fieldwork, Publishing and Community Engagement. SAA 78th Annual Meeting, Honolulu, Hawaii, April 3-7, 2013.
  • Tukey, John Wilder (1977). Exploratory Data Analysis. Addison-Wesley.