Computer Applications to Archaeology 2009 Williamsburg, Virginia, USA. March 22-26, 2009 1 Scientific Puzzle Solving: Current Techniques and Applications Florian Kleber and Robert Sablatnig 1 1 Institute of Computer Aided Automation, PRIP, Vienna University of Technology. Austria. Abstract An automated assembling of shredded/torn documents (2D) or broken pottery (3D) will support philologists, archaeologists and forensic experts. Especially if the amount of fragments is large (up to 1000), the compilation will not be feasible for a human puzzle solver due to cost and time. Approaches to solve the task of fragmented objects or puzzles can be divided into shape based matching techniques (apictorial) or techniques that analyze also the visual content of the fragments (pictorial), e.g. either image features or texture based analysis are done. Depending on the application, shape matching techniques are suitable for entities of the puzzle problem with small numbers of pieces (e.g. up to 20) and they cannot be applied to applications with hundreds of fragments due to the complexity. Also, artefacts like broken and lost pieces or overlapping parts of fragments increase the error rate of shape based matching techniques. This paper presents an overview about puzzle-solving techniques and their applications. It will introduce to the main problems in solving puzzles and will also focus on applications for the assembling of fragmented (ancient) documents.. Key words: Artefact Reconstruction, Document Reconstruction 1 Introduction Finding solutions for puzzles need a well-defined definition of the problem, since a wide variation and synonyms for the term “Puzzle” exists. Games like Rubik’s Cube, Puzz3D, Crosswords, the Tower of Hanoi or jigsaws may all be seen as a kind of Puzzle, whereas different strategies may be used for solving these. The most common form when talking about puzzles are 2D pictorial cardboard puzzles (also known as jigsaw puzzles). In history the idea of a pictorial puzzle goes back to John Spilsbury 1 who made a jigsaw puzzle out of a wooden map by cutting the borders of countries using a jigsaw. Spilsbury lived in London, working as an engraver and mapmaker 1 . The idea of his wooden jigsaw puzzles which he built in the 1760’s, was to create an educational tool, which can be used by children to learn 1 R. Tybon. Generating Solutions to the Jigsaw Puzzle Problem. PhD thesis, Griffith University, Australia, 2004. geography 2 . It is generally agreed, that this was the first jigsaw puzzle in history 1 . These puzzles made out of sheets of hardwood were followed by cardboard puzzles in the late 1800s and became a die-cut process in the 20th century 1 . The definition of puzzle in Merriam-Websters online dictionary is “a question, problem, or contrivance designed for testing ingenuity” 3 . To find approaches or algorithms to solve a puzzle, the “problem” has to be well-defined. Since torn or shredded documents belong to pictorial or apictorial jigsaw (see Section 2) puzzles, we have to formulate a definition of this issue. For instance Freeman defines jigsaw puzzles as an “arrangement of a set of given pieces into a single, well-fitting structure, with no gaps left between 2 E. D. Demaine and M. L. Demaine. Jigsaw puzzles, edge matching, and polyomino packing: Connections and complexity. Graphs and Combinatorics, 23(1):195– 208, 2007. 3 Merriam Webster Online Dictionary, Puzzle. http://www.merriam-webster.com/dictionary/puzzle[2] (accessed Jannuary 2009).