A Topographic contour lines reading system
Lin Zongjian, Lu Jian & Yan Li
Wuhan Technician University of
Surveying and mapping
China
Abstract
A semi automatic system for reading contour lines from topographic maps is proposed. Based on the map sheet image taking with CCD camera, a sequence of processing, such a line following, geometric rectification, mosaicking and DEM interpolation, are realized on this system.
Introduction
Topographic contour digitizing is heavy task in generating GIS data base. There are three ways to digitize map contours. The first is manual observing point height by overlapping transparent grid on the map sheet (Fig.1). The second is by using digitizing table, which is common on the market. Though the above mentioned two methods are popularly accepted, the efficiency is not very satisfying, and the accuracy depends on the operation. In the case of long time work, the accuracy are frequently going down due to the fatique of operator's eyes. The third way is automatically digitizing with scanner. However, fully automatic system is not functional well due to the complex drawing on the map and the limit capability of artificial intelligence at present.
A semi automatic system is proposed in this paper, attempting to make an optimal combination of automation and manual operation.
System components
The system components are shown in Fig. 2. Treasons of using CCD camera are: a) Geometric stability (can be calibrated) [1], b) high sensitivity with light, c) less volume, d) easy to change the image scale.
Fig.1 Contour lines reading
Fig.2 system components
