出版社：National Centre for Maps and Cartographic Heritage
摘要：The Topographic Atlas of Switzerland, short “Siegfried map”, is a historical mapseries covering the whole of Switzerland for the time period between 1870 and 1926.Georeferencing each single map sheet in a high quality is critical to minimize errorpropagation when subsequent tasks are to be performed, such as feature extraction or sheetcomparison.In this paper, we present a modular process consisting of six steps that facilitates thegeoreferencing of the scanned Siegfried map sheets by using tailored algorithms: The firststep consists of pre-processing the scanned map sheet using common image processingapproaches, removing non-relevant colour regions and enhancing the contrast and thesharpness of the map sheet. The second step performs image segmentation by detecting thecorners of the map frame using a pattern matching approach to determine the actual mapcontent. The third step involves the extraction of the coordinate grid based on the Houghtransform and subsequently the computation of the grid intersection points. In the fourth step,the coordinate information is extracted and translated into machine-readable form. In the fifthstep, the user can examine these automatically generated results and may manually correctthem. Finally, in the sixth step, the map sheet is automatically georeferenced usingquadrilateral-based bi-linear interpolation. This approach is used for georeferencing eachcoordinate grid cell separately and aligning the results rather than georeferencing the wholemap sheet at once. This way, distortions resulting from aging and scanning can be reducedwhile preserving the locations of the control points. The modularization of the process allowsto replace single components, when better algorithms will be developed. The aim is to use thisprocess to gradually georeference all Siegfried map sheets and to make them accessible in thegeodata4edu.ch geoportal.
