International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B2. Istanbul 2004 
  
less computation time. In these two test cases, the tolerance of 
model error is selected as 0.05 pixels. Thus, the patch for both 
sensors should be 160m by 160m and the terrain variation 
should be smaller than 500m. 
  
Model error of test data 
  
  
  
  
  
0.13 —- 
—$— QuickBird 160m* 160m (266pixel*266pixel) 
e ip SPOTS 160m*160m (64pixel*64pixel) 
2 
= 
= 0.08 
5 
— 005 
© 
Me) 
o 
= 0.03 
0.00 i re i 
0 500 1000 1500 2000 
Variance of Terrain(meter) 
  
Figure 11. Model error of test data 
3.2 Accuracy Analysis 
The ray-tracing method is applied to evaluate the orbit accuracy. 
Given the satellite orientation and image point, we calculate the 
intersection point of DTM and ray direction. We provide Table 
3 for the summary of accuracy. Table 3 illustrates the accuracy 
performance of GCPs and CHKPs, when 9 GCPs were 
employed. The accuracy of SPOTS and QuickBird are better 
than two pixels. 
Table 3. Root-Mean-Square error of orbit modeling 
  
  
  
  
  
  
  
  
  
GCP CHKP 
Unit: meter |GSD |RMSE E |RMSEN |RMSEE |RMSEN 
SPOTS 2.5. |1.78 1.96 3.98 3.12 
QuickBird |0.6  |0.55 0.48 0.71 0.87 
  
  
  
  
  
  
  
In order to evaluate the quality of orthoimage, we checked it by 
enough number of check points. Table 4 shows the RMSE of 
orthoretification. It is observed that the RMSE behaves 
similarly to orbit modeling. The orthoimage and error vectors 
of SPOTS are illustrated in Figure 12 and Figure 13. The 
orthoimage and error vectors of QuickBird are illustrated in 
Figure 14 and Figure 15. Please note that the accuracy results 
of orthoimages are similar to those in orbit modeling. This 
indicates that the accuracy loss is insignificant. 
3 
  
  
  
x 10 
T T T T T T T | 
7 | 
279r ; 4 
| 
| 
2.785 j- — 1 
x x i| 
278 ; \ H 
i x | 
t | 
ty | x | 
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> X x. # | 
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= x | 
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; | | e cs 
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© ca: aly 
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= | 
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+ X -— | 
\ ; 
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27451 
/ | 
£F | 
274m = 
Sd L | t | 1 1 | | 
25 26 27 28 28 3 3.1 32 
x 10° 
Figure 12. Error Vector for Generated SPOTS Orthoimage 
590 
  
5 
x 10 
  
T 
e 
N 
MN 
5 
ci 
N 
T 
  
Interna 
  
orthore 
is appli 
calcula 
be less 
Figure 
terrain 
actual | 
elevatic 
terrain 
smaller 
160m* 
elevatic 
analyze 
varianc 
patch s: 
QuickB 
minute: 
Compu 
Patch S 
Patch S 
Orthoin 
  
  
1 
  
Figure 14. Error Vector for Generated QuickBird Orthoimage 
  
Figure 15. Generated QuickBird Orthoimage 
1 1 1 
282 284 295 28 
x 10° 
  
Orthoin 
We us 
Backpr 
variatio 
do the 
result i: 
Backpre 
and bot 
spent 5: 
than 10 
Te 
  
Comput: 
(min) 
Terrain 
(m) 
Patch siz 
  
Terrain 
in a patcl 
Number 
  
  
3.4 Su 
The ex 
scheme 
than 0.0 
2 pixel