Honam Lee 
  
GROUND CONTROL POINTS ACQUISITION USING SPOT IMAGE - THE OPERATIONAL 
COMPARISON 
Kim Kam-Lae', Chun Ho-Woun", Lee, Ho-Nam"" 
"Professor, Myongji University, KOREA 
"Senior Researcher, Seoul National University Technology, KOREA 
“Senior Researcher, Chung-Ang Aerosurvey Co., Ltd., KOREA 
yhnhan C chollian.net 
Working Group III/5 
KEY WORDS: Ground Control Point, SPOT Image, Analytical Plotter, Digital Photogrammetric Workstation 
ABSTRACT 
This paper presents an investigation into the operational comparison of SPOT triangulation to build GCP library by 
analytical plotter and DPW (digital photogrammetric workstation). GCP database derived from SPOT image can be used 
to other image sensors of satellite, if any reasons, such as lack of topographic maps or GCPs. But, general formulation 
of a photogrammetric process for GCP measurement has to take care of the scene interpretation problem. There are two 
classical methods depending on whether an analytical plotter or DPW is being used. Regardless of the method used, the 
measurement of GCPs is the weakest point in the automation of photogrammetric orientation procedures. 
To make an operational comparison, five models of SPOT panchromatic images(level 1A) and negative films(level 
1AP) were used. Ten images and film products were used for the five test sites.. Photogrammetric measurements were 
carried out in a manual mode on P2 analytical plotter and LH Systems DPW770. 
We presented an approach for exterior orientation of SPOT images, which was based on the use of approximately 
eighty national geodetic control points as GCPs which located on the summit of the mountain. Using sixteen well- 
spaced geodetic control points per model, all segments consistently showed RMS error just below the pixel at the check 
points in analytical instrument. In the case of DPW, half of the ground controls could not found or distinguished exactly 
when we displayed the image on the computer monitor. Experiment results showed that the RMS errors with DPW test 
was fluctuated case by case. And the magnitudes of the errors were reached more than three pixels due to the lack of 
image interpretation capability. It showed that the geodetic control points is not suitable as the ground control points in 
DPW for modeling the SPOT image. 
1 INTRODUCTION 
The utilization of satellite imagery, especially SPOT, has been increasing rapidly in recent years. SPOT imagery meet 
all specification for 1:100,000 and has been shown to have 80% of the information requirements for 
1:50,000mapping(Gugan and Dowman, 1988). One of major capabilities of the SPOT system is suitable for 
cartographic work at scales of 1:50,000 to 1:100,000. The satellite is designed to be placed in a sun-synchronous orbit at 
about 832kilometers, with a 10:30 a.m. equatorial crossing time. Due to its ability to view areas at the oblique, 
successive imagery can be acquired at an interval of approximately two and a half days. 
A major focus in research activity is to increase the accuracy of rectified images by achieving subpixel accuracy when 
the image coordinates of the GCPs are calculated. Therefore, the strategy will not work if there is no (or not enough) 
GCPs that can be found on the images to be rectified. This is particularly true in many developing countries where large 
scale maps are less prepared and good quality of GCPs may be difficult to be found in an image to be rectified. On the 
other hand, the accuracy requirement for mapping in these less developed areas probably is relatively low and the 
manual method still can be used to locate the GCPs in the image(Zhou, 1990) 
Digital image processing has been made available to photogrammetry a number of techniques for automatic 
measurements of fiducial marks in inner orientation process and tie points. In recent years the potential of automating 
important photogrammetric processes has been demonstrated(Bjake, 1996). As of now, none of these approaches to 
automate the exterior/absolute orientation solve both the detection and the pointing problem without restricting 
constraints. Some hybrid solutions may well be possible, but are still not available. 
  
528 International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B3. Amsterdam 2000. 
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