海図等高線の自動抽出

抄録

It is a difficult task to collect X-Y coordinates (digital data) of contour lines on nautical charts with a digitizer by manually positioning the cursor. In this paper, therefore, we describe a method for extracting the contours from charts with the aim of automating the task. This method consists of four stages: thinning, tracking, extraction, and connection. The digital data of line images (include the contours) are created in the tracking stage by tracking the thinned line images obtained through the thinning stage. In the extraction stage, we classify the thinned line images into two types: contours and characters (include letters, the Arabic numbers, and symbols), based on the number of component pixels constituting the thinned line images and the closeness to smooth linear shape, and extract the contours only. Finally, the lack portions of contours caused by the insertion of the place names and altitude values are connected in the connection stage. Our proposed method attains the compactness and the simplicity, since the criterions in the extraction stage can be calculated from the only information obtained automatically by tracking the thinned line images.