Figure 1. A transportable test target on the field in summer 1995. 
  
  
  
  
  
  
  
  
  
C D 
size of target (m?) 1.0x8.0 3.0x3.75. 
4.5x6.25, 
6.0x7.5 
width of bars (cm) 3.0-12.0 75.0-150.0 
length of bars (m) 1.0 3.0-6.0 
range of spatial res. (l/mm) 25-100 40-80 
number of bars having the same 4 3 
width 
ratio of the width of bars $5 irregular 
between adjacent bar groups 
  
  
  
Table 2. The characteristics of permanent targets for 1:3 000 (C) 
and 1:60 000 (D). 
2.2 Aerial photography 
Test targets were photographed in summer 1995 using a Wild 
RC 20 camera. The experiment was carried out close to the 
permanent test field of the Finnish Geodetic Institute in 
Kirkkonummi, Finland. The characteristics of this test field is 
described in (Kuittinen et al., 1994). 
If two targets are properly placed compared with the flight lines 
it is possible to get satisfactory results for computing the 
average spatial resolution of the photographs. One of the targets 
is placed so that the bars are parallel and the other so that the 
bars are perpendicular to the flight direction. Figure 2 shows the 
approximate location of these targets in the image. Depending 
on the photo overlap measurements of spatial resolution in 
several places of the photographs can be made. Figure 3 shows 
the location of all possible measurements as a function of the 
image radius when 80% forward overlap is used. As can be seen 
the measurements are distributed quite evenly over the whole 
image area. The targets can be seen in altogether five images. 
100 
  
  
  
: : ; parallel bars 
flight direction a 
  
MAN 
image centre 
perpendicular bars 
  
  
  
  
  
  
Figure 2. The optimal location of two targets in the image when 
80% forward overlap is used. 
The altogether ten measurements allow the determination of 
AWAR-values for the photographs using the following 
equation. 
A 
AWAR = X——JR,T, (1) 
A 
where A; is the area of the circular zone between radius r; and 
rj, and, 
R; is the radial spatial resolution in the area A, 
T; is the tangential spatial resolution in the area A, 
A is the area of the whole image. 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B1. Vienna 1996 
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