Tollense field school - Part 5
Weblog
During the first two weeks of August 2022, students from Leiden University, University of Rostock and University of Göttingen have joined the Tollense Fieldschool to research an archaeological site in the Tollense Valley in northern Germany. The Cultural Heritage Agency participates in this fieldschool to support capacity-building of a younger generation maritime archaeologists and to facilitate international knowledge exchange. In these series of blogs, students and partners tell about their experiences. Read more about the international fieldschool and the Tollense valley in the first weblog. This edition, student Jaume Hernandes tells about photogrammetry.
Photogrammetry is a digital technique that allows making 3D digital models from 2D photographs of objects and features in the real world. During the Tollense Valley field school, this technique is used to document artefacts or features both on land and underwater. Additionally it is used to document the different stages or layers of the excavation on land. The process basically consists on taking photographs of the object or feature from different angles and with enough overlap between the photographs. A specialized software is then able to recognize the pixels that appear in several photographs and is capable of computing the distance and angles from which the photographs were taken. Then a point cloud of the object is generated and thereafter a mesh is made. Colour and texture is finally imposed on the mesh to create a 3D model.
Underwater photogrammetry is usually more challenging than on land. First, because it is more difficult to control the camera and have the right overlap between photographs due to the current and the need to maintain bouyancy. Secondly, because visibility is not ideal, especially in the shallow water conditions of the Tollense river: there is always a lot of sediment floating around and lighting is not homogenous with the sunlight rays having a big impact on the quality and color balance of the photographs. To help in the process, photogrammetry underwater is done by means of videos instead, from which frames are extracted and corrected, if needed, in a photo editing program. At the fieldschool, the students from the underwater excavation were taught on how to record and to process photo’s and films in ordert o create this 3D photogrammetry model. Below you see a few interesting results.
