International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B4. Istanbul 2004 
  
  
  
  
  
  
  
  
  
2 m diameter GCP 
  
  
  
  
  
  
  
  
  
bh 
.5 m diameter GCP 
Figure 2, Views of ground control points in satellite image. 
control points became more visible. The 2.5 m diameter 
ground control points were clearly seen and easily measured 
(Figure 2). 
Table 2 shows the mean errors that were obtained from the 
differences between ground coordinates and measured 
coordinates of the selected points on the satellite image. 
  
  
  
Ground RMS Average Errors 
control point (m) 
size m, m, mp 
(m) 
1,0 0,89: 0,51 1,03 
1,5 0,68 0,68 0,96 
2,0 0,71 0,48 0,86 
2,5 0,59 055. 0,81 
Table 2, Average errors in ground control points 
5. CONCLUSION 
Rectification process could be done without ground control 
points. But, accuracy of rectification with ground control 
points is higher. Certainly, using ground control points of 
bigger size than satellite image resolution may increase 
visibility of these points. Therefore, size of the control points 
is an important factor during analysis of images. Time of 
measurement, cost and accuracy are also important factors in 
map productions. Selection of an optimal size of ground 
740 
control points may decrease both cost and consuming time of 
application. Moreover, some application errors may take 
place as results of using big size ground control points as it in 
small ones. The contrast of ground's color and differences 
between points color are also important factors in visibility of 
points. Image interpreting and coordinate readings are related 
to operator's ability, eye sensitivity, image's quality and 
resolution directly. The present study showed that the most 
suitable size of ground control point was 2.5 m diameter 
points. But, in order to get a standard of required ground 
control point sizes, ground control points should be 
investigated in stereo, gray-scale and different resolutions 
images. 
6. REFERENCES 
Behdinian, B., 2002,"Generating Orthoimage From Ikonos 
Data", Proceedings of the 23rd Asian Conference on 
Remote Sensing, Kathmoandu, No. 173, 2002, Nepal. 
Cook, M. K., Peterson, B. A., Dial, G., Gerlach, F., Hutchins, 
K., Kudola, R. and Bowen, H. S., 2001, "IKONOS 
Technical Performance Assessment", Proceedings of 
SPIE Vol. 4381-10, 16-20 April 2001, Orlando, 
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