es 
s) 
ty À THEMATIC MAP READING SYSTEM 
Di Kaichang, Li Zongjian, Lu Jian 
st ( Wuhan technical University of Surveying and Mapping, P.R. China ) 
nd 
m ABSTRACT 
This paper presents a computer vision based thematic map reading system . It gets images 
from CCD camera with whole range of grey levels. À new methed for line extraction, called multi- 
criteria line following, is proposed. The procedure of data processing are described, such as 
st arc vectorization, topological structure generation, vector data compression, geometrical 
ie rectification, mosaicing and so on, In this system, areas and lengthes are mearured 
automatically and spatial statistical information are generated for GIS data base. The results 
of experiments and a test production show that this system has get to a practical stage in the 
  
  
  
St field of land source investigation, 
pe KEY WORDS : Computer vision, Thematic map reading, Line following, Topological structure 
> | 
>) 1 INTRODUCTION be taken when automatic processing meets 
Thematic map digitizing is a important way for e p gu to 
GIS data collection. At present, there 
mainly exist two means for map digitizing, 
one is manual operation by tablet, the 
other is scanning. The former has been 
widely used in productional units because 
of its simple operation, but it operates 
automatic processing and manual opertion. 
This paper describes the thematic map 
reading system in CV2. 
3. SYSTEM COMPONENTS AND PROCESSING DIAGRAM 
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
(49) | slowly and the accuracy and speed will 
"emi decrease when the worker is tired. Most 
(4) existing systems using the latter method 
are based on binary image processing 
(5) | techniques  ( Suzuki 1990, Musavi 1988 ) , IBM monitor 
such as binarization, thinning and so on. CCD camera — A/D D/A card 
They avoid a lot of manual operation and , PC otter 
work fast. But high quality map is requied a tabi ptor 
in these systems and the binarization i 
ay | threshold is difficult to chose. Different [| printer 
+ results are obtained with different Wis. 1  Sisten vemponents 
(3): thresholds. Unsuitable threshold will lead 
S Y to a lot of graphic editing tasks. 
m : | h The system cmponents is shown in Fig. l. 
"2er Drawing Masque fion | other ayetems, JA CCD camera is adopted because of its high 
(5) | computer vision Dates : raphe 208218 geometrical stability, high sensitivity and 
(2) | peu nA s Is Lea ene ; taken its being easy to change scanning pn Te 
S nn : : Ai camera is mounted on a mechanica 
ce function is de read topographical s map, scanning carríage and driven by electric 
(3) | Mamie, i ma W diu - mine motors in X, Y drictions. Map sheet B 
——— n 4 1 
n ; ; scanned patch by patch. The monitor is use 
e imitates ‚the human eyes to recognize : and to display grey level image. The produced 
(4) | follow lines based on : computer. — vision lines are overlaped on the image by a color. 
"€ techniques, This realizes the automation of This makes manual interaction easy. The 
€ line extraction, Data management and tablet is mainly used for interactive 
o transformation, such b post isa en operations, e. g selecting menu, editing 
Rosaicing and — topologica situciure graphics and inputing attribute codes. 
generation, are automatically performed 
based on photogrammetry and computer 
graphics, Efficient manual operations might 
Therefore a small size tablet ( say A3) 
is satisfying. The processing diagram is 
shown in Fig. 2. 
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