'anbul 2004 
T 
LL 
x 
++ 
eld. 
As was the case with IKONOS, the achievement of sub-pixel 
geopositioning with QuickBird stereo imagery required only the 
provision of the APs A, and Bj. However, the nature of the 
image coordinate residuals obtained in the bundle adjustment 
with shift parameters suggests that drift terms may also be 
warranted with QuickBird. The findings of Noguchi et al. 
(2004) support this view. The A, and B, biases reached 
magnitudes of 30m in the QuickBird stereo images. 
4. CONCLUDING REMARKS 
The impressive geopositioning accuracy attained with the RPC 
bundle adjustment with bias compensation supports the view 
that this sensor orientation model has the same metric potential 
as rigorous model formulations for HRSI. Implicit in this 
conclusion is that the RPCs produced by Space Imaging and 
DigitalGlobe are equivalent to the rigorous model, and thus 
there should be no concern regarding their applicability in 
stereo imagery covering any type of terrain. 
In comparing the accuracy results after bundle adjustment with 
ground control, we find not much difference between IKONOS 
and QuickBird. Both produce the highest accuracy in the cross- 
track direction. Also, in the test cases examined, QuickBird 
yielded slightly higher accuracy in height and IKONOS 
produced better along-track accuracy. The issue of residual 
systematic error in the along-track direction is of importance for 
users who wish to utilise sensor orientation models based on 
low-order empirical functions, such as the 3D affine model. 
Experience by the authors and others (e.g. Fraser & Yamakawa, 
2003; 2004; Noguchi et al., 2004; Hanley et al, 2002) has 
shown that success with models such as 3D affine 
transformation is highly dependent on the absence of higher- 
order error sources such as perturbations in scan velocity. While 
IKONOS Reverse scanned imagery appears largely free of such 
effects, the same is not always the case for IKONOS Forward 
scanned images and QuickBird imagery. Indeed the authors' 
recent experience with QuickBird Basic stereo imagery 
suggests that standard low-order empirical models do not yield 
very impressive accuracy results. On the other hand, where one 
has the opportunity of utilising bias-compensated RPCs, they 
should do so with every confidence of achieving optimal 
accuracy. 
5. ACKNOWLEDGEMENTS 
This work has been supported by Discovery and Linkage- 
Industry. Grants from the Australian Research Council. The 
authors also thank Space Imaging for the provision of IKONOS 
imagery, and DigitalGlobe and Sinclair Knight Merz for 
supplying the QuickBird imagery. 
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