332 
PS 9684 
    
  
pd 8680 
Figure 3-1 Contour lines drawn from SPOT data 
methods to extract accurate GCPs out of 
SPOT images were proposed. 
4.1 Line matching method 
In order to ‘extract a CCP in the area 
where no clearly  pointable- object as 
intersoction--of roads is exist, we tried 
to develop method to utilize linear object 
instead of point object as a GCP, because 
linear features can be found much easier 
than point object. 
In visual image interpretation, we can 
identify each linear features as roads. 
railways or streams by looking their 
unique patterns as number of curves, curve 
shapes. etc.. Those patterns tell us line 
to line correspondence between SPOT image 
and real ground. However, they can not 
tell point to point correspondence which 
is essential for the use as a GCP. 
The method proposed here is to get point 
to point correspondence from line to line 
  
Figure 4-1 Line feature on SPOT image 
338 
  
  
Figure 3-2 1:50,000 topographic map 
correspondence using line matching 
analysis. Ihe process and algori thm of 
the line matching method is as follows. 
(1) Measurement of a line feature 
Characteristic part of a line is to be 
measured at a set of points both on an 
image and on the ground as shown in figure 
4-1 and 4-2. 
(2) Line matching 
Two lines are to be matched by introducing 
two parameters for adjustment of x and y 
shift. 
(3) Adoption as a GCP 
The center of the "measured points is 
adopted as a GCP on the ground. And the 
corresponding image point is to be 
calculated with the x and y shift obtained 
by the line matching. 
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Figure 4-2 Line feature on a map 
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