Page - 177 - in Proceedings - OAGM & ARW Joint Workshop 2016 on "Computer Vision and Robotics“

RidgePointExtractionwithNon-Maximum SuppressiononIrregularGrids RichardScho¨npflugandHubertMara r.schoenpflug@stud.uni-heidelberg.de hubert.mara@iwr.uni-heidelberg.de Ruprecht-Karls-Universita¨tHeidelberg IWR–InterdisciplinaryCenter forScientificComputing FCGL–ForensicComputationalGeometryLaboratory Klaus-Tschira-Platz, 69120Heidelberg,Germany Abstract Assyriology is the studyof cultures related tocuneiformwriting,whichwasused formore than three millennia before Christ in the ancientMiddle East. Drawing hundreds of thousands of documents withcuneiformscriptmanually isa tedious taskand leads toademand forautomated toolsassisting the dailywork of assyriologists. The cuneiform script is a handwriting usingwedges (Latin: cunei) imprinted into clay tablets. Therefore the digitizationof cuneiform tablets is increasingly using3D- scanners thatprovide irregular triangulargrids inR3. Thesegrids i.e.meshesarediscretemanifolds, which are first filtered by usingMulti-Scale Integral Invariants (MSIIs) for visualization. Secondly theMSII filter results are used to extract points along the or ridges within the 3D-model leading to a digital drawing of e.g. a cuneiform tablet. Thereforewe choose the idea of the non-maximum suppression as used by the Canny edge detector for raster images. In contrast to the Canny edge detector we had to (i) to adapt to an arbitrary number of neighboring vertices, which have to be reduced locally in caseofflat areas; (ii) to implement anestimator for thegradient direction,which cannot be provided by theMSII filter; and (iii) to provide a border treatment as realworldmeshes havemissingparts. All theworkwas embeddedwithinourmodularGigaMesh software framework. Results are shown for synthetic and real data, demonstrating a computational complexity ofO(n), whichrequiresonlyoneparameter. Finallya summaryandanoutlookaregiven. 1. Introduction Cuneiformscriptwasusedformore than threemillenniabeforeChrist and isoneof theoldestknown writing systems. It is a handwriting in 3D, where imprints were made into clay tablets, using a reed styli [13]. This results in groups ofwedge shaped imprints forming the characters. The name cuneiform,originatesfromthewordcuneus forwedge.Drawingareplicationof thecuneiformtablets is an integral part of their decipherment. This drawing step is traditionallydonebymanually tracing photographsof the tablets andcan takehours or evendays. This is an almost impossible task taking into account thehundredsof thousandsofunpublished tablets. These tablets are important formany otherdisciplinesas theyprovide insights intoawidevarietyof topics ranging fromtheeconomicsof ancient societies to thefirst greatworksof literature, e.g. theepicofGilgamesh [10]. 177