3D recording and processing of historical wooden planks from the 2013 excavation at Karlsgraben
In this project, historical wet wood planks and wooden fastening materials of the Karlsgraben are recorded geometrically using high-precision and area-based 3D measurement technology. On the one hand, this is for pure documentation and, on the other hand, certain tool marks on the wood surface are to be digitally identified.
These are wooden planks from the 2013 excavation at Karlsgraben, which were dendroarchaeologically processed by the Bavarian State Office for Monument Preservation (BLfD) and are currently being conserved and stored in the restoration workshops of Waldemar Muskalla (Saulheim) on behalf of the BLfD. The 3D digitizations are part of the research project “Fossa Carolina: Link of the port networks on the Rhine and Danube. Studies on overcoming the European main watershed in the Middle Ages” in the Priority Program 1630 of the German Research Foundation (co-applicant Dr. Stefanie Berg-Hobohm). The follow-up and evaluation of the data within the framework of the project mentioned is carried out in cooperation with Dr. Lukas Werther from the Friedrich Schiller University Jena.
The Karlsgraben was the most important and most ambitious infrastructure project of the early Middle Ages in Central Europe: in 793, Charlemagne wanted to create a continuous shipping route between the Rhine and the Danube. The canal, which is about three kilometers long, is one of the largest archaeological monuments in southern Germany. An international excavation team led by Dr. During the excavation, Lukas Werther documented numerous pieces of timber, including mighty oak planks and wickerwork mats to stabilize the canal slopes. Thanks to the high level of groundwater and the covering with sediment immediately after construction, the medieval wooden structures have been preserved and are in exceptionally good condition. (Source Dr Werther)
The i3mainz recorded the wet wood objects with a 3D scanner from industrial metrology (GOM ATOS III Triple Scan structured light projection scanner), whereby a measurement volume was selected in which a 3D point resolution on the wood surface of 0.25 mm is achieved. The 3D resolution can be influenced by various factors, such as reflection or the nature of the surface (e.g. very dark surface) of the object. The three-dimensional recording of the wet wood objects takes place before the conservation, which is why the aforementioned influencing factors affect the data quality and resolution. In order to be able to completely record the individual wet wood planks, the objects must be scanned from both the top and the bottom side. Both sides are linked via signs that were attached to the side areas of the respective measurement object after consultation with the restorer. The measuring activities started in 2016 were continued and completed in 2017.
In two measurement campaigns, 24 wet wood objects, which were broken down into several parts (45 in total) in the course of the dendro-archaeological investigation, were successfully recorded from the restoration workshops in Saulheim using the above measurement method. These 45 fragments were virtually reassembled into 24 overall objects. After the complete acquisition and generation of closed 3D models, the data was converted into a so-called elevation model (DEM) in order to make it usable for common GIS applications. In the GIS software used (QGIS & GVSig), different tools are available for the visualization of this type of data (raster data), whereby representations in the form of edge separation, contour lines, inclination visualization and relief shading should be mentioned. Furthermore, the 3D data is available in standard exchange formats (e.g. PLY, STL), which can be used in this form with different software packages or can serve as the basis for a physical 3D print. A web-based application was developed for a more flexible approach to the provision and analysis of the 3D data, which does not require the installation of special software. The aim is to make the large and therefore storage- and computation-intensive 3D data available with the help of a web server, whereby the 3D data can be viewed and analyzed on the client side using a 3D viewer integrated into the website. Initial considerations for an expansion of the provision in this form for all result data already exist and require follow-up financing.