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
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?
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.