Extraction of roads from topological maps using a parallel extraction algorithm

Abstract

AbstractOne of the most important techniques in drawing recognition and understanding is to extract the effective components from a complex image according to the purpose of analysis. This paper considers the map which is the most complex among images, and describes an automatic method to extract roads. In general, roads are represented in the map by parallel lines. Consequently, the extraction of roads from a map is formulated as a problem of extracting parallel lines. A method is proposed which directly extracts parallel lines from the image and describes the parallel lines by the spacing and the path of the central line. Two technical problems are contained in this approach. One is the parallel‐line extraction, which extracts parallel‐line areas (inside the parallel lines) from the image, and the other is the line vectorization, which determines the coordinates for the path line of the extracted area. For the latter, numerous proposals have been made such as line‐image thinning and line tracing, and the problem is almost solved. From such a viewpoint, this paper discusses primarily the former, i.e., the parallel‐line extraction. One of the difficult problems in the extraction of parallel lines from the image is the processing of the area where parallel lines intersect. A generalized expansion‐contraction of the image is proposed to solve this problem. The proposed method is applied to a map issued by the National Geographical Institute, and is verified as effective as a method of road extraction.