THE PRACTICE RESEARCH Of IKONOS-2 POSITIONING AND ITS ACCURACY 
IN TIBET OF P. R. CHINA 
Chen Chujiang*® Li Deren“ Zhu Qin* 
? The School of Remote Sensing Information Engineering, Wuhan University, 129* Luoyu Road, Wuhan, P.R.China- 
cjchen@public.wh.hb.cn 
b : 3 ; . 5 ; : i . sis 
China Communication Second Highway Survey, Design and Research Institute, 498* Yinwu Ave. Wuhan, P.R.China 
KEY WORDS: Research, Ikonos-2 Satellite Imagery, High Resolution, Accuracy, Analysis, Spatial Information Sciences 
ABSTRACT: 
Tibet is located in the Qinghai-Tibet high plateau in the west of P. R China. In Tibet, the altitude is very high, the weather is 
extremely bad and few people live there. Especially in the Himalayas area, the terrain undulates frequently and sharply, and its 
relative height has reached to 3000m. The national foundation control network has not covered the region yet and there is no large 
scale relief map and high accuracy geospatial data to be used. It is very difficult to survey with the terrestrial method, because of the 
limitation of the work condition and the traffic condition. Ikonos-2 stereo satellite imagery has the advantages of high ground 
resolution and wide coverage. It can be used to collect the precise geospatial data and produce the large scale map. As it is different 
from the aerial photogrammety, the Ikonos-2 RPC, the transform of the datum, the mode of the control point distribution and the 
method of Ikonos stereo triangulation have been studied by the author. It shows that the precision is under £0.95m and +0.55m for 
plane and height respectively in high mountain area with several ground control points in 1000 square km. These results proof that 
not only can Ikonos-2 be used in high accuracy spatial position and large scale mapping, but also it need a little field control 
surveying. Ikonos is very valuable in the Tibet area where the conditions of terrain, traffic and weather are all extremely awful. 
1. INTRODUCTION 
Photogrammetry or airborne GPS phtogrammetry is a high 
precision method to obtain the geospatial data, and be used in 
practice widely. However, it needs a certain Ground Control 
Points(GCPs) on specifically position. This is a particular 
difficult thing in Tibet of P.R. China where there is no national 
foundation control frame and the terrain condition is very 
horrible. 
Ikonos is the commercial high resolution satellite launched in 
September, 1999. The Im panchromatic image and 4m color 
image are produced by Ikonos sensor. Unlike other sensor for 
mapping, instead of physical sensor model, the RPC model is 
provide to ultimate users(J. Grodecki, 2001). RPC not only can 
do the spatial transformation between image space and object 
space with very high accuracy(M. Kumar, O. T Castro, 2001, E. 
Baltsavias, M. Pateraki, etc, 2001, C. S. Fraser and H. B. 
Hanley, 2003), but simplify the physical sensor model and can 
be implement in various digital photogrammetric system(G.Dial, 
J. Grodecki, 2002, T., C. Vincent and Y. Hu , 2001). However, 
the practice researches of Ikonos imagery are limited in WGS- 
84 system, there is few such researches that transform from 
image space to national coordinate system, especially in the 
high altitude, the terrain undulates frequently and sharply area, 
such as the area of Qinghai-Tibet high plateau and Himalayas in: 
the west of P. R China. 
According to the Space imaging estimate, the Ikonos accuracy 
is the worst in Himalayas area. But the Ikonos image has the 
advantage of multi-spectrum, the wide coverage, high 
resolution and the image geometry stabilization, however, it is 
very high value-added in the area of high altitude and difficulty 
terrain condition compare to field survey and aerial 
phtogrammetry for the spatial data can be obtained rapidly and 
precisely without too much ground control points and the field 
work can be reduced greatly. 
The authors have developed the transform between the Ikonos-2 
image space and the national coordinate system based on the 
RPC, and examined and analysed the results of block 
adjustment with various control schemes in a practical project 
near Himalayas mountain, and the encouraging results of high 
positioning accuracy have been obtained. 
2. THE TRANSFORMATION BETWEEN IMAGE 
SPACE AND THE NATIONAL COORDINATE SYSTEM 
2.1 The transformation between the image space and the 
WGS-84 system 
The datum of Ikonos image is WGS-84. The transformation 
based on rational polynomial coefficient(RPC) is as follow: 
20 
> LINE _NUM _COEF; * p;(B,L,H) 
F === 
S'LINE_DEN _COEF; * p;(B,L,H) 
i=l 
20 (1) 
>" SAMP_NUM _COEF; + p;(B,L,H) 
i=l 
Fuse 
Y, SAMP DEN COEF, e p(B.L,H) 
i=l 
  
  
Where B.L,H=the normalized coordinate of the object space 
in WGS-84; 
X, Y-the normalized coordinate of the image space; 
For the Ikonos camera, the inner orientation elements are 
known and fixed up among the imaging, but the outer 
orientation elements consisted of the position and the attitude of 
the sensor changed from line to line. Because there are orbit 
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