Contributions to computer-aided analysis of cuneiform tablet fragments
Creators: name: Fisseler, Denis Bernd
Publisher: name: Technische Universität Dortmund
Year: 2019
Subjects: subject: Cuneiform
subject: Geometry processing
subject: Mesh segmentation
subject: Wedge extraction
subject: Statistical script analysis
subject: Segmentation framework
subject: 004
subject: Keilschrift
subject: Geometrieverarbeitung

description: This thesis presents methods for computer-aided three-dimensional analysis of digitized cuneiform tablets, an ancient type of writing documents. Since cuneiform script is predominantly conserved in the form of fractured clay tablet fragments, identifying matching fragments is a central task of manuscript reconstruction. This goal can benefit from the increasing 3D digitization of cuneiform fragments, which offers access to highly accurate cuneiform representations. The main contribution of the thesis is a novel model-based method for the extraction of individual cuneiform wedges and associated wedge geometries from 3D scans, which can serve as a base for a statistical analysis of script features. This new automated approach enables access to large amounts of accurate quantitative cuneiform script features, which were not accessible by previously available 2D methods and can be employed for script similarity-based identification of candidates for fragment joining. A central aspect and challenging task is the robustness of the presented extraction method against scanning issues and mesh errors. This is achieved by employing a watershed-based wedge area extraction operating on a surface distance field with a subsequent constructive multi-stage model fitting. The extracted wedge models are refined by a wedge type classification followed by an effective wedge validation to handle false detections on fracture faces and damaged surfaces. An evaluation with respect to extraction rates, robustness, and performance shows the suitability of the developed methods that goes beyond an application purely for cuneiform fragment joining. To address some compromises made during the wedge extraction regarding the representation of complex features, a fast supplementary approach for extracting skeletal surface features is presented. These features provide an alternative readable cuneiform representation and are created using a thinning approach on an approximated distance field. The quality of the resulting skeletons is optimized by employing a complex junction resolution, branch pruning and branch simplification methods, where both pruning and simplification can be used to adjust the resulting representation to different use cases. Aside from manual feature analysis, possible application scenarios also include providing a representation that can be handled by GraphCNNs for retrieval related tasks on cuneiform structures. The cuneiform segmentation methods are complemented by a set of visualization concepts for a cuneiform segmentation framework. This includes a hierarchical concept for data handling and persistent storage of the generated segmentation data. Beyond, methods for fast rendering of large meshes, visualization methods to achieve good depth perception, detail enhancement, and semi-realistic surface shading are integrated. In order to not only address application scenarios like fragment joining and collation related tasks, the framework provides a sophisticated, highly interactive, and flexible segmentation data visualization that additionally offers fast geometry selection methods. A good accessibility of the generated data is guaranteed though an XML-based file format for storing segmentation data and through providing flexible data export methods. Although the framework is primarily intended for real-time segmentation, most segmentation methods can also be scheduled to process large numbers of fragments without user interaction. All presented methods are evaluated with respect to performance aspects and their suitability for a set of philological use cases. The developed methods can be used flexibly in the scope of many aspects of the investigated application cases. This does not only apply to the automated feature extraction, but also to manual analysis aspects, which were discovered only by the new availability of the methods. The usability of the framework is underlined by the fact that it is actively being used by philologists from the Hethitologie-Portal Mainz, an established online resource in Hittitology.