A Virtual Paleolithic: Assays in Photogrammetric Three-Dimensional Artifact Modelling

Access to Paleolithic artifact collections is often constrained due to the cost of travel, governmental restrictions, and the rare nature of unique specimens. In the current high-tech climate, researchers are turning their attention to alternative ways of gaining information about and analysing these materials. The recent boom in three-dimensional replication of cultural materials including lithic, bone, and fossilized specimens, has provided researchers with an invaluable analytical tool with which to carry out new and innovative studies. In this paper, the authors review a cost-effective, photogrammetric-based three-dimensional modelling system that utilizes digital artifact images and commercial software. Requiring only a notebook computer and standard digital camera, this methodology allows for the production of digital computer models from which important morphological information can be obtained. The modelling process is exemplified through two case studies—the replication of an Acheulian handaxe and the ongoing modelling and analysis of Middle Paleolithic refitted cores from the site of Taramsa Hill, Egypt. In both cases, the forensic software package iWitnessTM was used to identify points on the artifact surface that were then converted into points in three-dimensions. The wireframe models produced from these points were then imported into 3DS Max 9TM where the model was skinned and subsequently manipulated to produce cross-sections and calculate morphometrics such as surface area, volume and center-of-mass. Aside from the analytic advantages it affords, three-dimensional modelling ultimately provides the opportunity for increased sharing of data, ideas, and results among members of the geographically distributed paleoarchaeological and paleoanthropological community. Digital models can be sent electronically via the Internet without the restrictions typically associated with valuable archaeological specimens. Photogrammetric modelling methods are ideal for this purpose because the images required to create virtual models can be easily obtained from collaborators worldwide and subsequently processed in a location of the researcher’s choosing. Consequently, photogrammetric three-dimensional modelling represents a useful and accessible alternative to more expensive laser scanning technologies. InTRoDuCTIon T use of three-dimensional modelling in archaeological analyses has become increasingly popular over the last decade. At the recent 2007 Society of American Archaeology Annual Meeting in Austin, Texas, an entire preconference session was dedicated to the range and uses of three-dimensional scanning techniques in archaeology. The growing interest in such approaches stems, at least in part, from the increasing accessibility of modelling technologies. Not only have a wide range of commercial alternatives become available in recent years, the declining cost of these technologies has made three-dimensional modelling more accessible to researchers. With technological literacy at an all time high, archaeologists are more than ever taking advantage of this promising analytical and illustrative tool. There are, however, challenges to integrating these kinds of methodological approaches into one’s research program. Mafart (2002) points out in his review of the extensive colloquium concerning three-dimensional imaging in archaeology at the XIV UISPP Congress: PaleoAnthropology 2008: 158−169. © 2008 PaleoAnthropology Society. All rights reserved. ISSN 1545-0031 T. AlExAndrA SuMnEr Department of Anthropology, University of Toronto, 19 Russell Street, Toronto, Ontario, M5S 2S2 CANADA; alexandra.sumner@utoronto.ca AndrEw T.r. rIddlE Department of Anthropology, University of Toronto, 19 Russell Street, Toronto, Ontario, M5S 2S2 CANADA; andrew.riddle@utoronto.ca “In prehistoric archaeology, image acquisition often requires a skilful technician able to adapt industrial surface scanning techniques to archaeological soils or objects, the services of a computer technician, and the cooperation of the team in charge of the archaeological site. The level of technical complexity is such that no investigator can have the full range of competency and yet each must know and understand the roles of the other players”(1). While this may be true in some circumstances, it is demonstrated here that the skills and knowledge required to model archaeological specimens can, in fact, be acquired and applied within a reasonable period. Three-dimensional modelling has been applied to a multitude of archaeological research programs at varying scales of analysis, from individual artifact reconstruction (Schurmans et al. 2001) to virtual site reproduction (Zabulis et al. 2003). The range of materials examined in these studies include, but are not limited to, stone (Boehler et al. 2003; Riel-Salvatore et al. 2002), bone (Mafart et al. 2004; A Virtual Paleolithic • 159 rosenberger and Hogg 2007; wood et al. 1998), ceramic (Kampel and Sablatnig 2001), and textiles and paper documents (debevec 2003; Hawkins et al. 2001). riel-Salvatore et al. (2002) describe a computer-based methodology for the automation of lithic refitting using a laser digitizer to scan flakes from a sample of previously refitted Ahmarian cores. Surface morphologies of the digitized models could then be compared to identify refitting fragments. Clarkson et al. (2006) present a method for quantitative evaluation of flake scar patterns on an artifact by recording individual scar orientations in three dimensions using a stylus-based digitizer. In contrast to two-dimensional approaches for studying surficial scar patterning, this and similar methodologies have great potential for exploring core reduction strategies from a perspective that better represents the nonplanar morphology of lithic artifacts. Matusik et al. (2002), and Műller et al. (2005) describe image-based modelling systems capable of replicating detailed objects and materials. At the macro-scale, three-dimensional modelling techniques can be used to capture site information for the production of visually informative images of archaeological sites. Barceló et al. (2003) describe the creation of digital terrain and elevation models for Shamakush VIII, a shell midden site in Tierra del Fuego, Argentina. With their models it was possible to graphically represent and manipulate strata, providing a better understanding of formation processes that generated the stratigraphic sequences. Losier et al. (2007) apply GPS data to the Gocad modelling tool to produce three-dimensional reconstructions of excavation trenches at the Syrian site of Tell ‘Acharneh. Similarly, a combination of photogrammetric and three-dimensional scanning techniques was applied to the mapping of the Pinchango Alto site in Palpa, Peru (Lambers et al. 2007). In line with the work of Pollefeys et al. (2001), the authors here review their methodology for incorporating photogrammetry with three-dimensional computer modelling to digitally reconstruct Paleolithic artifacts. A comprehensive explanation of the modelling process is provided first, detailing the equipment required and how it was used to create virtual artifacts. The process is further explained through two test-cases—the reconstruction of an Acheulian handaxe and the more extensive application of the process to Sumner’s doctoral research on Middle Paleolithic (MP) lithic core reduction. In the final section, the potential for the proposed methodology in Paleolithic research is expounded upon, and it is concluded that photogrammetric modelling is uniquely suited to Paleolithic research because it allows one to create virtual models of specimens that may be inaccessible to the researcher using only digital images. MeThoDology Photogrammetry involves the calculation of reliable measurements from photographs and digital images. Two common applications for photogrammetry are in the production of maps from aerial photographs or satellite images and the forensic reconstruction of accident scenes. While map production largely involves working in two dimensions, measurement in three dimensions is also possible albeit with the use of more complex mathematics. Provided a sufficient number of images are available, one can determine the shape and relative size of the three-dimensional objects depicted. Further, this information can be used to recreate the form of an object in a virtual environment. The method described here entails the calculation of three-dimensional points on the exterior surface of an artifact. Points are identified from multiple digital images of the same object taken from a variety of incident angles. Surface points are situated in three-dimensional space and can be connected to create a ‘skin’ that approximates the exterior surface of the object being modelled. The hardware required for photogrammetric modelling consists solely of a digital camera and a computer. As stated above, all calculations of artifact dimensions are made from images, thus no specialized measuring equipment is necessary. The digital camera is used to capture images of the subject that are then uploaded to the computer for processing. High image quality is preferred, so a digital camera with support for 1024 x 768 or greater pixel resolution is recommended. While SLRs provide superior control over light and focus during image acquisition, a standard point-and-shoot model is sufficient. Traditional film cameras also may be used but typically offer lower resolution and the resulting images are more difficult to transfer to digital form. Although a notebook computer is recommended over a desktop model for ease of transport and overall convenience, it is not a requirement. Both computers and digital cameras are sufficiently commonplace today that their acquisition should come with minimal difficulty and cost to most researchers. For processing the artifact images, one also requires two computer applications—one for photo