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Title
Mapping without the sun
Author
Zhang, Jixian

275
3. EXPERIMENT
3.1 Data-Sets
There are 5 groups' data for experiment, including along-track
stereo image pairs and across-track stereo image pairs.
® SCENE01 n SCENE02 : Data are stereo SPOT-HRG
images, covering the area in France with 5m
resolution^ 12000 column * 12000 row).
(D SCENE03: The SPOT-HRG image covers the area in
France with 10m resolution^ 6000 column * 6000 row).
(3) Stereo Radarsat images cover the Erhai area in
China ,with the sizes (8949 column * 8598 row )and
(12865 column *12679 row).
© Stereo pairs of SPOT imagery and Radarsat imagery,
which cover the Hulu Island in China, with the sizes are
(6000 column * 6000 row) and (7971 column *8910 row).
(5) Stereo IKONOS images cover Beijing City in China, with
lm resolution, and the sizes are ( 7853column * 19043
row)and ( 7648 column * 19043 row).
3.2 Experiment I
The first experiment with the RPC model was performed on the
satellite images deriving from various sensors to confirm the
accuracy of forward and inverse transformation is up to
standard.
Select points which are uniform distribution on all over the left
image to project to the ground by the forward RPC Model, and
then project the ground points to the image back to obtain some
points as result. Table 1 compares the coordinate of image
points obtained by calculation with selected initially. The
variance is presented as an accuracy index. Table I shows that
no big differences exist in terms of points’ coordinates. This
outcome indicates that the accuracy of forward and inverse
RFCs are precision reached.
Image
Maximal
difference in
line
Minimal
difference in
line
RMSE in line
Maximal
difference in
sample
Minimal
difference in
sample
RMSE in
sample
SPOT-HRG
6.42E-02
8.79E-09
1.30E-02
1.25E-02
6.31 E-10
2.30E-03
RADARSAT-1
2.39E-03
-3.92E-10
1.30E-05
1.43E-03
1.84E-09
1.33E-05
IKONOS
2.22E-06
4.96E-11
1.39E-06
7.68E-06
1.82E-11
1.76E-06
QUICKBIRD
-5.03E-05
2.79E-10
9.91E-06
3.94E-05
5.98E-10
7.80E-06
SPOT
3.77E-04
1.22E-08
2.42E-03
5.02E-04
9.27E-09
9.88E-05
Table. 1 Accuracy of the forward and inverse transformation (pixels)
3.3 Experiment II
The experiment on the satellite images for epipolar resampling
is carried out.
Before the epipolar resampling process, a two-step pre
processing is applied for the original images. First, the
geometrical rectification is performed on the satellite stereo
images using The Satellite Imagery Block Adjustment system
software. Second, the correction coefficients of image
coordinates deriving from the first step are used for affine
transformation of image points.
Therefore, bias-corrected images can be used to test the
epipolar resampling algorithm.
Do the same experiment to the five pairs of stereo-images. First,
from the left image, a stochastic point is extracted to project to
the ground according to the given elevation level. Change the
height of the corresponding object point twice along the light
ray connecting the perspective centre and project the object
points onto the right image. There are three image points on the
right image deriving from the projection. Fit these three points
to be the right epipolar line.
And then, choose 11 points evenly on the right epipolar line to
project to the ground, the same as before, change the height of
the corresponding object point and project the object points
onto the left image. There are 11 image points on the left image
deriving from the projection. Fit these 11 points to be the left
epipolar line.
Figs (1) to (7) show the generated conjugate epipolar lines and
display them on the stereo-pairs. Fig (8) is a flow diagram
showing the performance of the method of epipolar resampling.
left image (SCENE01) right image (SCENE02)
Figure 1. SPOT-HRG scenes
left image (SCENE03) right image (SCENE01)