Efficient preprocessing of generating DEM from digitized contour map
Koji Kajiwara, Ryutaro Tateishi
Remote Sensing and Image Research center,
Chiba university
1-33, yayoi-cho,
Chiba City, Chiba, Japan
Abstract
In order to reduce the processing time and human power in reprocessing of generating DEM from digitized contour map (raster image), an efficient method is proposed as follows:
- High speed and simple algorithm for automatic processing in some parts of editing digitized contour image. Interactive editing procedure utilizing information obtained by automatic editing processing in the other parts.
- A automatic recognition of numerals on principal contour lines for efficient assignment of altitude to contour lines.
Introduction
For the generation of Digital Elevation Model (DEM) from digital raster image which digitized from topographic maps, it is necessary to identify the contour lines and assign altitude to them. At present, this preprocessing requires much time and enormous accumulated topographic maps to be digitized, it is important to develop efficient method. However, it is difficult to develop the full automatic system including editing process. If such a system developed, it will be high cost system which needs powerful computer for the complex algorithm. So we propose to combine the automatic processing with interactive processing effectively. This approach enables the automatic processing algorithm can be realized by utilizing the information which obtained in automatic processing.
Methodology
Fig. 1 shows the outline of processing. First, multi level contour image is produced by digitizing a topographic map using the drum scanner. Binary contour image which is the object of editing process is built by binrizing multi level contour image. Multi level contour image and binary contours image are source of preprocessing.
After first step of editing process, all contour liens on both multi level image and binary level image are traced., In this process, various information is obtained. We call this information contour attribute (described in detail in the section 4). The contour attributes stored in attribute file. This file and edited binary contour image will be final output of preprocessing after modification of editing, recognizing principal lines, recognizing numerals represented altitude and assignment of altitude to contour lines. As shown in
Fig. 1, basic processing form is analysis of the information read from attribute file and modification of the attributes by results of processing.
In this study, we propose the method of altitude assignment which is composed of two steps. In the first step, altitude is assigned to principal contour lines using recognitions of numerals which represent height value.
The intermediate contour lines are assigned in the second step utilizing the height value of principal contour lines. To realize this method, identification of principal contour lines and recognition of numerals are required.
