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
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All
Aid
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AH
A 1.1
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— 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.