151 
accuracy of different resolution images, a sampling experiment 
of different resolution images is performed. In this experiment, 
other than continues sampling, only the integer sampling is 
considered. The MS image pixel size is 16 times of PAN image 
pixel size. Figure 1 from case 1 to case 10, 10 figures show 
different sampling error of comer. The equal probability of 
sampling error is supposed. The statistical result is showed in 
table 1. 
• Center in PAN image 
• C enter in MS image 
i-i MS image 
□ PAN image 
® Ground object 
É$ Object extension 
Case 4 
Figure 1, Sampling error of corner, case 3 and case 4. 
■ C enter in PAN image 
• C enter mMS image 
!_J MS image 
□ PAN image 
Ground object 
Obj e et e xtension 
Case 9 Case 10 
Figure 1, Sampling error of comer, case 9 and case 10. 
Table 1 shows that the average sampling error of comer is 2.82 
pixels (PAN). 
No 
Deviation 
Probability 
1 
3.53 
1/3 
2 
3.53 
1/3 
3 
6.78 
1/3 
4 
0.71 
1 
5 
1.58 
1/2 
6 
3.81 
1/2 
7 
2.91 
1 
8 
1.58 
1 
9 
2.55 
1 
10 
3.53 
1 
11 
3.53 
1/3 
12 
3.53 
1/3 
13 
4.95 
1/3 
Weighted mean deviation=2.82 (pixels) 
Table 1. Sampling error of comer and its probability 
Figure 2 shows the different sampling error of gravity center in 
different situation. The statistical result of sampling error of 
gravity center is showed in table 2. 
■ Center in PAN image 
• Center in MS image 
l-i MS image 
□ PAN image 
S Ground object 
Figure 2, Sampling error of gravity center, case 1 and case 2. 
Table 2 shows that the average sampling error of gravity center 
is 1.12 pixels (PAN). This figure is much smaller than that of 
comer by 60 percent. That means the gravity center is more 
suitable than comers to be used as tie points, because the 
gravity center has higher geometric accuracy than comer.