Extracting Contour Lines Utilizing Features of a Raster Image Topographic Map

Abstract

Member of JSCE, Dr. Eng., Sanei Co. Ltd. (3-13-26 Kagamiyama, Higashi-hiroshima, 739-0046 Japan) 3Member of JSCE, Assist. Prof., Hiroshima Inst. of Tech. (2 -1-1 Miyake, Saeei-ku, Hiroshima, 731-5193 Japan) It is a difficult task to automatically extract contour lines from a raster image topographic map and give each contour line its inherent elevation. In this paper, the authors propose an automatic contour line extraction algorithm based on the continuity among the contour lines. All of the paints on a contour line indicate the same elevation, the difference of elevations between every neighboring contour line is constant, and most wide contour lines have numeral arrays pointing out their inherent elevations. By employing the information of these features, the shapes and elevations of contour lines can be extracted and recognized. Usefulness of the proposed algorithm is demonstrated with several practical maps.