Full text: Proceedings of the Symposium on Global and Environmental Monitoring (Part 1)

Combined Application of Pattern Recognition Methods 
in Automatic Digitization of Contour Line Maps 
Jun Yang 
The Digital Elevation Model (DEM) has been applicated more and more in spatial 
analysis, regional planning, project designing, topographical displaying etc. Many 
governmental and private institutions are engaged to gather digital elevation 
information from different sources. The digitization of existing maps is a highly 
efficient and economic way-, if the qualities of the maps are sufficient. But the 
most used manual method of digitization cannot cover the increasing require 
ments. Therefore a system has been developed to automatic structuring of con 
tour line maps from scanned data. The system has been tested in the Institute 
of Cartography, University of Hannover. 
A contour line map usually contains three kinds of information: 
1. the contour lines, many of which are drawn in regularly dashed lines, 
2. the numbers showing the heights of the contour lines and 
3. the special symbols describing the sudden change of the terrain, 
such as cliffs and outcrops. 
This system is composed of the following procedures: 
Scanning and vectorization. A map is transformed into image by a scanner. The 
raster data have to be converted into vector data in order to reduce the data 
and accelerate the processing. 
Segmentation of contour lines from texts and symbols. At first all kinds of data 
are in one level. The recognitions can be carried out only succesively and me 
thods used for every kind of object are different. Therefore it is neccesary to 
separate the data into different object subset before classification. To distingu 
ish the different objects the features which contain the characteristic informa 
tions, e.g. line length, line width, line curvature and number of lines on nodes, 
are extracted. Upon this feature space a training process should be effected to 
get the parameters that will be used in classification. At first step the contour 
lines are selected from another data set by means of Quader Classification me 
thod . 
Recognition of contour lines. The contour lines for example in Germany Basic 
Map Series 1:5000 were drawn in dashed lines excepting the contour lines at 
the 10 meters vertival interval. The different line width, line length and gap 
length have been used to construct the line signatures for representing different 
vertival interval. The line signatures have the defined structures.

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