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,
Florida.
Interna
Dare,
[
]
Dial, €
]
Dial, G
N
Fraser,
I
I
?
Grodeck
I
I
/
Hanley,