One of the learning scenarios which is currently being developed at the University of Bonn is an introductory course into Greek archaeology, that aims to widen the students’ knowledge concerning the basic genres like pottery and sculpture.
Therefore, a large amount of 3D models is required, but unfortunately, the already existing ones are just in a few cases freely available yet. Due to the ongoing restoration works in the Akademisches Kunstmuseum of the University of Bonn the comprehensive collection of plaster casts is largely not accessible right now. Therefore, a small group from Bonn, consisting of VR experts, archaeologists and interested students, went to Tübingen to record 3D models of plaster casts, vases and other small finds in the museum of the university. The recording session also offered the possibility to introduce students from Tübingen and Bonn to the methods and procedures of 3D recording as part of a holiday course.
To provide the students with a preferably complete overview from the recording of the object up to the data processing there were four stations. Two techniques were practiced at three of these stations: Laser scanning and Image Based Modelling. The applicability of these methods depends heavily on the objects themselves, for example their size and complexity.
The first station taught Laser scanning, which involves a Laser scanner whose laser beam scans the object surface, measures the distances and creates the 3D model. Different Laser scanners are available whose application mainly depends on the object, that should be recorded. In our case the scanner is suitable for objects of a height of 30 cm and more and was therefore used to record sculpture. It is particularly appropriate for complex objects with strong undercuts or overlaps as we for example know it from Hellenistic sculpture. Another major advantage of laser scanning is the fact that the 3D model is already being generated during the process of recording and can be postprocessed directly. Depending on the size, a sculpture can either be scanned completely at once or in several partial scans that are merged later, as it was necessary, for example, in the case of the sculpture of Heracles Farnese, who has a height of more than 3 m.
Two other stations practiced Image Based Modelling, also known as photogrammetry. As the name suggests, the 3D model is generated from pictures which are taken from numerous overlapping perspectives. Generally, this method is applicable for objects or contexts of every size but since a lot of pictures are necessary, it is far more time-consuming in case of larger objects and is, thus, preferably applied to smaller objects. Furthermore, this method is particularly suitable when the texture of the surface is a crucial feature of the object, for example in case of the Attic painted pottery. In Tübingen we used Image Based Modelling for smaller sculptural artworks, like plaster casts of portrait heads, e. g. the portait bust of emperor Augustus.
Besides the plaster casts we used Image Based Modelling especially for original objects: terracotta figurines, small architectural elements, like the Tarentine limestone capitals, and pottery (see all recorded objects on the SketchFab account of the Bonn Center for Digital Humanities). If the objects are smaller than 25 cm it is advisable to use a special setup: it consists of a light tent for ideal lightning and a turntable. The camera and the turntable can be controlled by a smartphone application which enables the automation of the recording process to a large extent.
Objects with a shiny surface pose a particular challenge for the recording process. This especially applies to the Attic black- and red-figured pottery: the red and black surface show different reflective properties, with the black surfaces being much shinier as a result of the three phase-firing. Due to movement of the object or the camera the incidence angle of light is changing from picture to picture. During subsequent processing into a 3D model, the program calculates an average value for the texture of the surface, so that black surfaces become grey. To remove those unintentional surface reflections polarization filters are being used for the lights and the camera, which make it possible to almost completely eliminate surface reflections and enable the best possible result. The reflective properties of the red and black surface can then be reassigned when post-processing the model.
At the fourth station the students learned the processing of the recorded data: on the one hand the further processing of the scanned objects and on the other hand the different steps to generate the 3D models from the pictures. In three days we were able to record a total of 80 objects of different size, genre and difficulty, which, together with the already existing and freely available models, form a great basis to build up a virtual collection of plaster casts and original objects. In Tübingen, there will be a follow-up course in summer in which the students will continue to work on the calculation processes. The aim is to establish a 3D recording team at the institute.
We would like to thank the custodian Alexander Heinemann, who followed our work with enthusiasm and excitement, for making the 3D recordings possible and the museum team for the pleasant stay. Furthermore, we want to thank the students for their motivated participation and endurance.
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