Morphology based an automated approach for editing raster digitized contour maps
Chen Xiaoyong, Shunji Murai
Institute of Industrial Science, university of Tokyo, Japan
Michio Kawahara, Yoshinori Yajima, Kentaro Narigasawa, Doihara Takeshi
Atsugi Technical Centre, Asia Air Survey Co., LID., Japan
Abstract:
The substantive preprocessing invariably required by current method to convert scan digitized contour maps into a digital elevation data base severely limits the use of raster scanned for many practical applications. This paper presents and efficient "morphology based" approach to edit contour lines digitized from topographic maps. In contrast to the predominantly manual and semi-automatic techniques currently in use to scan and capture topographic data from hard-copy contour maps, the proposed method mathematical morphology theory to reconstruct the topological connections of contour liens in rasterized contour maps. The approach has been successfully tested on a 1:50000 scale digitizing Japanese topographic map by suing C language and X window system on SUN IV workstations.
Introduction
Extraction of DTM data from existing topographic contour maps is of great importance to many applications such as landscape analysis, land form classification, civil engineering planning and design, geographic information systems, etc. For this reason, this kind of research has been widely interested in recent years [Baker, et.al. 1981; Callaham, 1983; Greenlee, 1987; Sukit and Murai, 1988, 1990; Chen and Li, 1990; Yang, 1990; Lin, et.al. 1990]. But up to now automated raster-vector conversion and elevation labeling of raster contour lines also need many manual interruptions and editings, more efficient methods and software are needed to speed up this procedure[Lichtner, 1988; Chen, 1990].
Based on mathematical morphology, this paper presented several kinds of relation based full-automated raster contour segmentation and linking methods. The key to these methods is the use morphological parallel image processing operators to automated get the topological relations between broken contour line points. By using these topological relations, together with the criteria of direction and distance, we can easily realize automated editing of raster contours. For improving the reliability of editing long distance
broken contour lines, we proposed a post-editing method based on the morphological boundary of local broken contour areas. This method will be very useful to automated processing contour maps in complicated areas, such as urban areas. The approach has been successfully tested on a 1:50000 scale digitizing Japanese topographic map by using C language and X window system on SUN IV workstations.
Basic Procedures of system
For automated generation DMT from scanned topographical contour maps, we need many processing, such as scanning, thinning, contour image segmentation, raster contour editing and linking, generation of structure lines and geomorphologic points, raster-vector convertion, and DTM generation. These procedures can be simply described by the following flow chart(Fig.1).
Fig.1. Program Flow Chart of the System
Fig.3. Sgmentation of Contour Image
This paper doesn't with elevation labelling and DTM interpolation, which can be found in (Sukit and Murai, 1988, 1990; Chen and Li, 1990; Sircar, 1991).
Thinning and Segmentation
Color and gray-value contour image can be obtained from topographical maps by canning and A/D conversion. The methods of color image segmentation and gray-value image theresholding can be found in (Sukit and Murai, 1990; Nagao, 1980), and we do'nt want discuss these problems in this paper. After these processing, we can get binary contour
image. usually, the binary contour image is not one pixel thickness, and includes many kinds of noise, such as grid line, letters and symbols for identifying contour lines. Therefore, we should do the processing of thinning and image segmentation firstly.
