Image-based modelling approach to the documentation of Crvenkuša cave site Site description Archaeological excavations at the cave complex Crvenkuša – Tamnica – jama Suhi Rumin were conducted during the fall of 2018 as part of the Croatian Science Foundation funded project „Where East Meets West – the Cetina River Valley as an Ancient Pathway of Communication (Cetina Valley Survey)“, directed by prof. dr. sc. Helena Tomas. Crvenkuša Cave is located in the Dalmatian coastal hinterland ca. 10km north of Sinj. It is a part of a large cave complex. Its front part is approximately 15m long and 9m wide with the entrance oriented towards SE. The cave was previously known from literature and its surface pottery was identified as dating back to the early Neolithic Impressed Ware. In the fall of 2018 a small test trench 1x2m was excavated at the entrance part of the Crvenkuša Cave. The thickness of layers above the bedrock was ca. 70cm. This trial excavation confirmed the existence of early Neolithic remains, but they were found mixed with archaeological material from various time periods, pointing to the secondary context of the finds. Such a secondary context could be an outocme of postdepositionlal disturbances caused by the collapse of cave walls and the ceiling. It is also possible that a portion of the archaeological material found in the cave originated from the plateau above the cave which was affected by erosional processes. Miroslav Vukovid Department of Archaeology Faculty of Humanities and Social Sciences University of Zagreb I. Lučida 3, 10 000 Zagreb, Croatia mivukovic@ffzg.hr References • Agisoft, L.L.C., 2011. Agisoft PhotoScan user manual. Professional Edition, Version 0.8. 0 (accessed 03.05. 2011.) • Gallay, M., Hochmuth, Z., Kaňuk, J. and Hofierka, J., 2016. Geomorphometric analysis of cave ceiling channels mapped with 3-D terrestrial laser scanning. Hydrology and Earth System Sciences, 20(5), p.1827. • Lerma, J. L., Navarro, S., Cabrelles, M., & Villaverde, V. (2010). Terrestrial laser scanning and close range photogrammetry for 3D archaeological documentation: the Upper Palaeolithic Cave of Parpalló as a case study. Journal of Archaeological Science, 37(3), 499-507. • http://www.agisoft.com/forum/index.php?topic=1797.0; accesed 29.11.2017 6th scientific conference Methodology and Archaeometry, 6th and 7th of December 2018 Faculty of Humanities and Social Sciences of the University of Zagreb Helena Tomas Department of Archaeology Faculty of Humanities and Social Sciences University of Zagreb I. Lučida 3, 10 000 Zagreb, Croatia htomas@ffzg.hr Documentation The documentation process regarding cave sites follows an established practice where the location of the trench is shown in both a topographical ground plan of the cave and as a cross section for the visualization of elevations. The metric data needed for the generation of these plans is usually collected by using simple laser distance meters or tape measures, with the level of detail determined by the surveyor who takes measurements at a smaller or a bigger interval. The resulting two-dimensional documentation is therefore to some extent subjective, since the person recording the data determines the level of detail needed. This cave site has provided us with a perfect opportunity to test out a three dimensional approach to data acquisition. The ability to capture data in 3D and transfer it to a digital scan/model enables us to create a much more objective dataset for the reproduction of plans than the dataset obtained by conventional methods. Since the location of our trench was at the enterance part of the cave where light was abundantly available, we were able to capture sequences of images needed for the creation of photogrammetric 3D models. The dataset had to include the trench, as well as two additional light sources that were placed in its proximity. Four reference points were measured by using a total station placed at the cave entrance; those points were later on used to georeference the 3D model. The images were taken with a RICOH GR II camera set on interval shooting every 5 seconds, and mounted on a Manfrotto mononpod for easier handling. The uneven surfaces of the cave walls and ceilings provided quite a challenge in the process of covering the whole surface with 80% overlap in photo sequences. Although some smaller areas remained uncovered, the resulting 3D model was extrapolated in Agisoft PhotoScan LLC, by using 244 photographs with the resolution of 4928x3264 pix. The dense point cloud was constructed out of 11 544 232 points, from which the mesh was extrapolated and textured. The image acquisition process took 36 minutes, and an additional 20min were spent on sketches and the measurement of reference points with the total station. Advantages The photogrammetric 3D model was used to generate an orthophoto of the cave, with the trench shown from an bird’s eye perspective. The nature of cave sites and the methods of excavation make the profiles of the trench an important source of information. Their manipulation and data extraction is much simpler in 3D then when it has to be reconstructed from ordinary photographs. The 3D dataset enables us to bisect the model wherever we please, and in the case of trench profiles this means that we can segment the individual profiles and present them on the same plan. This becomes especially useful when the position of the trench within the cave system has to be shown in cross section with associated elevations. The 3D model could also potentially serve to improve our understanding of the site formation processes. Similar workflows involving laser scanners enabled researchers to gain a better understanding of geomorfological processes involved in the formation of caves and cave sites (Gallay et. al. 2016). Drawbacks Using image based modeling in a cave environment can be a daunting task. In most cases caves are extremely dark environments , where artificial light is usually the only source of light. In those conditions the usability of photogrammetric 3D models comes into question, although some case studies have shown remarkable results achieved by using camera flash lights. A laser scanner would be more appropriate tool for cave site documentation as it not light dependant (Lerma et al 2010). The temperature of the colors in the photographs taken for the 3D modeling process can give us false information regarding the layering of the different stratigraphic units. Nikola Vukosavljevid Department of Archaeology Faculty of Humanities and Social Sciences University of Zagreb I. Lučida 3, 10 000 Zagreb, Croatia nvukosav@ffzg.hr Marcel Burid Department of Archaeology Faculty of Humanities and Social Sciences University of Zagreb I. Lučida 3, 10 000 Zagreb, Croatia mburic@ffzg.hr Conclusion Using image-based modeling in cave environments is a quick cost-effective way to create detailed plans and cross-sections needed for the documentational aspects of the project. The usability of the method in low light caves should be further tested, and the camera flash light method should also help with the temperature (K) of the photographs themselves. The documentational process for this particular site was shortened by a few hours because of the application of image based modeling. The resulting documentation is a much more objective and detailed dataset than that provided by conventional measuring techniques. The dataset and its potential uses as a tool in geomorphometry will be explored further. Fig 4: Impressed Ware fragments found at the surface and in the trench excavated at the entrance part of Crvenkuša Cave Acknowledgements We would like to thank N. Buzjak, I. Rašid, T. Rubinid. D. Pleše, M. Bašid and N. Vuglešid for the permission to use the tophografic plan of the Crvenkuša-Tamnica-j. Suhi Rumin system. We would also like to thank our colleague J. Triplat and all of our students who participated in the excavations. Excavation was financially supported by the Croatian Science Foundation and the Ministry of Culture of the Republic of Croatia. Fig 2: Plan of the cave system Crvenkuša – Tamnica – J. Suhi Rumin Fig 3: Left: Aerial photo of the cave, enterance circled in red; Right: close up photograph of the cave enterance Fig 1: Location of the cave site in the Cetina river valley Fig 5: Crvenkuša cave site entrance Fig 6: Upper left: crossection of the cave and the excavated trench; upper right: bird’s eye view of the cave; lower left: vi ew of the trench with artifical light sources; lower right: the complex image sequence used for the generation of the 3D model The four images shown above are images of the pointcloud used for the generation of the 3D model