The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part BI. Beijing 2008
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X n ,Y n ,Z n : the normalized coordinate value of object points in
ground space.
p 1, p 2, p 3 and p 4 : the polynomial coefficients
pl(X n ,Y n ,Z a ) = a 0 +a \X + a 2 Y + a 3 Z + a 4 X 2 + a s XY + a 6 X Z + a ? Y 2 +
aJZ + a 9 Z 2 + a w X } +a u X 2 Y + a n X 2 Z + a n X Y 2 +
a u XYZ + a ]S XZ +a^ 6 Y +a l jY^Z-ba lf( YZ~+a l gZ'
KOMPSAT-2 RFM is forward method which can be calculated
from ground coordinate (Latitude, Longitude, Height) to image
coordinate (Column, Row). Auxiliary file(***.rpc) gives RPC
parameters for “ground to image” location model.
A least-squares approach is utilized to determine the RPC
a n ,b n and d n f rom a three-dimensional ground coordinates
generated using the KOMPSAT-2 MSC camera model. The
basic relationship of the KOMPSAT-2 MSC camera model that
describes the ground coordinates in term of sensor coordinates
is realized by the co-linearity condition in which the
KOMPSAT-2 MSC perspective center, an image point and the
corresponding ground point are assumed to be on one straight
line. The 3D ground coordinates of object points in RFM are
generated by intersecting the rays emanating from a 2-D grid of
image with a number of constant elevation planes.
3. EXPERIMENTS AND RESULTS
3.1 Test Data
The experiments were conducted on a Level 1G panchromatic
KOMPSAT-2 image of worldwide area. (See, Figure 3) The
KOMPSAT-2 Level 1G imagery acquired on February 17, 2007
to February 9, 2008. The total number of test images data set is
121.
In this study geometric accuracy of KOMPSAT-2 images have
been thoroughly examined based on KOMPSAT-2 direct sensor
model results from KOMPSAT-2 IRPE system. For ground
coordinate calculation from satellite data, we need the
ephemeris data every scan line but KOMPSAT-2 meta
data contains the ephemeris data every 1 second with
respect to the WGS 84. According to, “KOMPSAT-2
Users Manual”, Lagrange interpolation of the ephemeris
and attitude data are used to calculate data set for every
scan line.
Figure 4. The location map of KOMPSAT-2 geometric
accuracy test area.
The GCPs were extracted from IKONOS ortho-rectified image
data by Google Earth. GCPs were features in imagery such as
cross road and the comers of buildings. In each test image, used
GCP number is about 16 GCPs.
3.2 Geometric Accuracy without GCPs
The ground coordinates of KOMPSAT-2 PAN using ephemeris
data which are calculate from satellite GPS, star tracker and
Gyro sensor were calculated by direct sensor model. The Figure
5 shows the results of implemented KOMPSAT-2 direct sensor
models.
Figure 5. Summary of geometric accuracy
Figure 5 shows the 90% Circular Error measurements for the
KOMPSAT-2 Level 1 product from IRPE for the February
2007 and the February 2008 data sets. Figure 5 shows the
geometric accuracy in KOMPSAT-2 from just using provided
ephemeris, attitude and time data. The average of geometric
accuracy is 51.65 m(CE90). This accuracy met the KOMPSAT-
2 system specification of 80m CE90 for both panchromatic and
multispectral imagery.
3.3 RPC characteristic
KOMPSAT-2 data is provided RPC with NITF format also. The
main purpose of provided RPC has been used to replace the
KOMPSAT-2 direct sensor model results with ephemeris,
attitude and time data and also users can make the ortho-
