ting up the first order polinomials by four anchor points
of each case, and the further statistics have been
performed. The following Table 1. is the result of statis-
tics (unit is pixel).
Table 1.
| Indirect Approach | Direct Approach
|
|
Average MSE | Mx=0.0150 My=0.0169 | Mx=0.0133 My-0. 0079
| |
Maximum Error | Ex=0.2486 Ey=0.6426 | Ex=0.1679 Ey=0. 4340
| |
Minimum Error | Ex=0.0011 Ey=0.0003 | Ex=0.0015 Ey=0.0002
23 |. decl =.
As there is one value of MSE of point for each
case. So we have the average MSE of point. From Table |,
we can find out that the error of point for direct
approach is less than that for indirect approach.
6.3 The precision of orthophotomap
The final results of two approaches in rectifi-
cation are two orthophotomaps, on which the check points
have been selected to fit up the first order polinomials
for examining the precision. Table 2 is the fitting error
of point on those check points (unit is meter).
Table 2.
Point No. | Indirect Approach | Direct Approach |
| line | pixel | line |. pixel |
1 | 74.4 | 2.3 | 1.3 ! Tus
| | m | |
2 | 1.0 | 2.3 L. 5.27. 15: 04.4 |
3 rs -10.8 | za. | 4.4 | 3.3 |
4 -6.8 | -10.6 | 6.5 | 4.3
5 | 1.9 | E | 5,5 | 74. 6
6 us 8.9 | 73.9 | 29.8 | =f) 1 |
1 | 26.5 | 6.1 = 3.8 |
8 3 4. 6 | 14.4 | —8 2.3 |
MSE 6.08 6.27 4.40 5.66
Table 2 shows us that the rectification results
have both the precision of subpixel.That is about one half
of a pixel. Furthermore the precision of direct approach
is higher than that of indirect approach. So taking into
account the imaging geometry of SPOT image and employing
the corresponding flexible algorithm for the rectifi-
cation are very important to assure the quality of geome-
tric processing. As the last results, Table 2 has
proved the correctness, reasonableness, and flexibility
of the principles and methods suggested above.
7 Conclusion
When performing digital geometric corrections for
SPOT images, it is not only necessary, but also flexible
to rectify the prejective distortion due to relief. The
suggested principles and methods based upon the imaging
geometry of SPOT have been successful in making first use
of collinearity equations for linear-array scanned images.
According to the characteristies of SPOT images, The
employment of direct approach in rectifications has shown
us for the first time that it has more advantages to this
kind of images.
34
References,
i.
Wang Zhizhou, 1990. Principles of Photogrammetry
€ With Remote Sensing ), Publishing House of Surveying
and Mapping, pp. 1-10.
Shu Ning, 1988. On the Digital Geometrical Recti-
fications for the Spacelab Images by Using Collinea-
rity Equations. Journal of Wuhan Technical University
of Surveying and Mapping, Vol.13, No.3.