282
image and the refined second-order RFM orthorectified image
are compared in Table 1:
CKP
Traditional RFM (RMS)
Refined RFM (RMS)
X
Y
Total
X
Y
Total
1
11.392
15.828
19.502
4.246
6.032
7.377
2
13.849
9.316
16.690
4.813
3.280
5.824
3
3.718
8.088
8.902
0.324
2.107
2.132
4
21.844
15.692
26.896
7.588
4.275
8.709
5
28.153
47.507
55.222
14.792
16.377
22.068
6
19.101
35.256
40.098
14.011
12.266
18.622
7
8.078
11.556
14.100
0.972
4.136
4.249
8
31.796
14.616
34.995
9.228
2.250
9.498
9
15.372
11.467
19.178
6.281
1.374
6.429
10
4.612
36.583
36.873
0.876
12.227
12.258
mean
15.791
20.591
27.245
6.313
6.433
9.717
max
31.796
47.507
55.222
14.792
16.377
22.068
Table 1: Residual errors table of CKPs (meter)
Figure 8. RMS plot of CKPs based on refined RFM
Figure 9 and Figure 10 illustrates the comparison of errors
vector of CKPs using in different orthorectified methods. Figure
9 illustrates errors vector map of CKPs based on traditional
RFM; Figure 10 illustrates the errors vector map of CKPs based
on refined RFM. Obviously, the geometric positioning accuracy
of orthorectified image by using refined RFM has been greatly
increased no matter in the direction or in the size.
The residual errors of the traditional first-order RFM
orthorectified image: in X direction, the mean of residual errors
is 15.791m, and the maximum is 31.796m; in Y direction, the
mean is 20.591m, and the maximum is 47.507m. The mean of
total residual errors is 27.245m, and the maximum is 55.222m.
The maximum residual error occurs at CKP 5, whose height is
also maximum shown by DEM, while the chosen CKP 10, 20,
23, 26 around the CKP 5 just lie out of the high area. With such
GCPs involved in fitting, RFM does not consider the height
change of the CKP 5 properly. The distribution of residual
errors at each CKP is shown in Figure 7:
According to the table analysis shows: compared to traditional
RFM, the refined RFM has improved the accuracy considerably.
Due to the increase of the number of GCPs from 6 to 15, the
fitting of RFM becomes more reasonable, with the error limited
in a certain range. Using the refined RFM to rectify the image
can eliminate radiation distortion, tangential distortion, affine
distortion, and the correlation such as translation and distortion,
which results in a good improvement. Meanwhile, experimental
data shows that: in X direction, the mean of residual errors is
6.313m, and the maximum is 14.792m; in Y direction, the mean
is 6.433m, and the maximum is 16.377m. The mean of total
residual errors is 9.717m, and the maximum is 22.068m. The
distribution of residual errors at each CKP is shown in Figure 8:
Figure 9. Errors vector map of CKPs based on traditional RFM
Figure 10. Errors vector map of CKPs based on refined RFM
