The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B4. Beijing 2008 
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A 2 
A3 
A4 
A 5 
A ( j 
AT 
A8 
A9 
A 10 
All 
Aid 
A 13 
AH 
A 1.1 
A16 
— 1 0m Errors were magnified by 1 00 times 
Figure 3. GCPs distribution on ground in QuickBird imagery. 
3.3 Results with updated RPCs using GCPs 
Conclusion can be drawn that there are some systematic errors 
with the RPC provided by DigitalGlobe from the results above. 
The horizontal error is about 23 meters; the height error is about 
16 meters. To get a better 3D coordinates, GCP must be added 
to the RFM. To study the importance of different configurations 
Figure 4. Vector graphics of discrepancies between the RPC 
generated and GCP coordinates in horizontal direction. The 
errors were exaggerated 100 times. 
of GCPs, a typical 16 distributed GCP configuration are 
employed as Figure 5. Different combinations of the number 
and distribution of GCPs are tested to find the patterns and 
effectiveness of the configurations. 
3.3.1 Accuracy improvement in object space 
Plane 
—z 
1 2 4 6 8 10 12 14 16 
GCP Number 
M. 
8 10 12 14 16 
GCP Number 
(b) 
-m—x 
Y 
•"iK""—" Plane 
-* Z 
(C) 
Figure 5. Figures of Accuracy with different GCP Number in object space: 
(a) .translation model; (b) scale and translation model; (c) affine model; (d) second-order affine model. 
• Translation Model: At least 1 GCP is needed for this 
model, and there is no adjustment during calculation. The plane 
accuracy is about 3 m for 2 m as the best, height accuracy 
ranges from 3 m to 5 m with 3 m for the best. Translation model 
in object space is not sensitive to GCP number, and addition of 
GCP cannot improve accuracy significantly. When the GCP 
number reaches 6, the accuracy is sensitive to the GCPs distri 
bution and addition.