276 
Figure 3: RADARSAT scenes 
SPOT image Radarsat image 
Figure 4: SPOT and RADARSAT scenes 
Figure 5: Zoom out of SPOT and RADARSAT scenes 
Figure 6: Stereo IKONOS scenes 
Figure 7: Zoom out of IKONOS scenes 
For these five pairs of images, the vertical parallaxes of the 
conjugate epipolar lines are not more than 1 pixel by the means 
of manual visual interpretation. As is shown from Fig(l) to 
Fig(5),these images are across-track stereo pairs on which the 
conjugate epipolar lines are approximately horizontal, and as is 
shown from Fig(6) to Fig(7),IKONOS images are along-track 
stereo pairs on which the conjugate epipolar lines are 
subvertical. Therefore, it is necessary to emphasize that the 
IKONOS imagery should be resampled in accordance with 
“sample” when generating epipolar images, and the images’ 
width and height are interchanged compared with the original 
images. Finally, the paper generates the conjugate epipolar 
imagery by the means of experiment II. 
3,4 Accuracy assessment 
This section is performed to evaluate the accuracy of the 
generated epipolar imagery. 
The first step is to extract a pair of conjugate epipolar lines 
generated by experiment II, and choose 10 points which are 
uniform distribution on the left epipolar line. The second step is 
to project the 10 points to the right image using the RPC Model. 
If the line-pairs generated are rigorous conjugate lines, the 
points on these two lines should be one-to-one correspondences. 
That is to say, a point is on the left epipolar line and its 
conjugate point should be on the right epipolar line. According 
to this theory, the authors compute the distance from the right 
image points obtained by projection to the corresponding right 
epipolar line. The distance is presented as the accuracy 
standard. Results of the five group images are presented and 
compared in Table (2). 
Image 
Maximum 
Error 
Minimum 
Error 
RMSE 
SPOT-HGR 
0.468 
0.037 
0.253 
RADARSAT 
10.008 
0.009 
4.028 
SPOT— 
RADARSAT 
4.235 
0.297 
2.715 
IKONOS 
0.042 
0.0001 
0.022 
Table2 Accuracy of epipolar images (pixels) 
Image 
X 
Y 
SPOT-HGR 
-0.0005 
0.031 
RADARSAT 
0.104 
0.027 
SPOT—RADARSAT 
0.0155 
0.037 
IKONOS 
-0.014 
-0.190 
Table 3 Orientation accuracy of stereo-images (pixels)