(edit) 
  
T 
= 
1/4" CMT 
(input &output) 
EWS (SPARCstation2) 
8mm tape drive 
(back up) 
   
GP.IB 
Image Scanner 
(scanning) 
Figure 1 : Typical hardware configuration of simple up-dating system 
-scanner used for aerial 
photographs, 
-1/4" cartridge disk drive used for loading 
and storing the digital map, 
-workstation used for overlaying, extracting 
changed parts and editing, 
-8 mm tape drive for back up 
digitizing 
Using these hardware, updating work is done 
in the following flow. 
a. digitization of aerial photograph 
b. overlaying aerial photograph on map 
c. visual extraction of changed parts 
d. edit 
Computer programs corresponding to these 
works a,b,c,d are required. Among these, the 
program for overlaying is essential in this 
system. 
3. FLOW OF UPDATING WORK 
3.1 Digitization of aerial photograph 
As quality of digitization of aerial photograph 
406 
influences visual interpretation very much, 
scanning should be properly conducted 
according to the quality of final result required. 
There are two types of scanner, transparent 
type and reflective type. Transparent type, 
which can attain high geometric accuracy but 
is expensive, is for film, and reflective type, 
which 1s common in small size scanner, is for 
print Therefore, reflective type scanner is 
better from the point of simple updating 
system in case high geometric accuracy is not 
required. 
In case geometric accuracy is important, aerial 
photograph should be digitized in finer than 
25 pm by transparent type scanner. However, 
if scanning pitch is too fine, data size of 
scanned photograph become too huge. 
3. 2 Overlaying aerial photograph on map 
There are three types of methods for 
overlaying used in this system. Those are as 
follows. 
a. method using orthophoto 
b. meth 
central p 
C me 
photogra 
Principle 
Figure 2. 
(1) Meth 
In this n 
using S 
Second, 
the dig 
correspoi