The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part BI. Beijing 2008 
The direct sensor model calculates the orbital parameters 
directly by using the position vector. Based on the collinearity 
condition, an image point corresponds to ground point using the 
employment of the orientation parameters, which are expressed 
as o function of the sampling time. 
This ephemeris information through the KOMPSAT-2 POD 
system and the produced POD(Precision Orbit Data). 
The calculation of ground coordinates on an arbitrary image 
coordinate (u,v) is 
The RFM is a generalized sensor model that uses a pair of 
rations of two polynomials to approximate the condition 
equation. 
2.1 DIRECT SENSOR MODEL 
The direct sensor model of KOMPSAT-2 MSC is realized on 
the co-linearity condition. The spacecraft perspective center, 
image point and the corresponding ground point are assumed to 
be on one straight line using six basic coordinate systems. The 
origin of sensor coordinate system is considering coincided 
with the origin of the spacecraft which is located at the 
spacecraft center of mass. 
The Figure 1 gives a description of basic sensor model of 
KOMPSAT-2. 
v Nj 
Interior 
Exterior orientât! 
Figure 1. Direct sensor modelling for KOMPSAT-2 geometric 
calibration and validation 
In from image coordinate system to sensor coordinate system, 
the main cal/val parameters consist of focal length, distortion 
which one is the LOD distortion the other is LOS distortion. 
After those distortion corrected using by GCP(Ground Control 
Point)/ICP(lmage Control Point) with under 0.3 pixel accuracy 
and bundle adjustment, KOMPSAT-2 image data are provided 
to users. The cal/val items of from sensor coordinate system to 
body coordinate system compute to correct occurring 
misalignment come from between star tracker sensor and MSC. 
The Orbit Coordinate System as translation body coordinate 
System, the produced rotation angle of roll, pitch and yaw 
rotate and transfer the coordinate system from star tracker and 
gyro sensor of KOMPSAT-2. The measured attitude data are 
recorrected by the KPADS (KOMPAST-2 Precision Attitude 
Determination Subsystem). Earth-Centered Earth-Fixed 
Coordinate System(ECEF) is transfer from orbit coordinate 
system to ECEF as coordinate system, using satellite position 
and velocity vectors of the satellite measured from GPS sensors 
of KOMPSAT-2. The measured from GPS of the KOMPSAT-2 
satellite system, the satellite of position, velocity and time 
information are transferred to the OBC, after this, that 
information is transferred to ground station through the S-band. 
x-x s ~ 
X 
Y-Y s 
= V. m ecef • M° rbit • M Body • 
K m Orbit iV1 Body m Sensor 
y 
Z-Z s 
z 
where, 
MSf • fr° m or b't coordinate system to ECEF 
Meody : from body coordinate system to orbit coordinate 
system 
M Tl, ■ ft™ sensor coordinate system to body coordinate 
system 
[x, y, z] T : Scan line coordinate 
[X s , Y S ,Z S ] T : Satellite position from ephemeris data 
[X, Y, Z] T : Ground coordinate 
k : scale factor 
2.2 RFM 
The RPC for the KOMPSAT-2 MSC sensor is generated from 
the resulted KOMPSAT-2 direct sensor model using the RFM. 
The RPC generation in KOMPSAT-2 IRPE system consists of 4 
main parts as shown in Figure 2. 
Figure 2. KOMPSAT-2 RPC generation workflow 
The model uses a pair of rations of two polynomials, as shown 
in equation 2. 
PKX n J n ,Z n ) p3(X n ,Y n ,Z n ) 
p2(X n ,Y n ,Z n ) " p4(X n ,Y n ,Z n ) 
where, 
r n , c n : the normalized row and column index of pixels in image. 
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