1.
direction. The general accuracy of this model is about 0.8 meter
in plain direction with slightly more than 0.7 meter for the best,
0.9 to 1.6 meters in height direction with 0.9 meters for the best.
• The second order affine model is the most complex
model with 6 GCPs for the solution at least. The solution with
only 6 GCPs available are instable, affected much by the distri
bution of the GCP, thus not suitable for the accuracy improve
ment. When 8 GCPs are used, the solution is much better with
about 2 meters in plane direction and 4 meters in height. With
more than 4 redundant GCPs, this model provides better accu
racy than the models above, but at the same time this model is
also less stable than others. With 16 GCPs distributed evenly in
the test region, the highest accuracy can be obtained for this
model with 0.56 meter in plain direction and 0.75 meter in
height direction.
4. CONCLUSIONS
This paper presents experimental results of a study on accuracy
assessment based on QuickBird across-track stereo imagery
using GCPs and different transformation models applied on
RFM in both object space and image space. Two QuickBird
images acquired in the Shanghai area at different time and
highly accurate GPS survey points as GCPs are used in the
experiment. Different methods and GCPs distribution patterns
are tested. From the analysis above we can conclude that
although the QuickBird across-track stereo imagery was
collected at different time, they can still meet the DigitalGlobe’s
23CE90 standard. The addition of GCP distributed on both
ground and the top of buildings greatly improved the
positioning accuracy. Analysis of the results obtained by both
object and image space models using different numbers and
distributions of GCP shows that, with the same redundancy of
conditions, the second-order models achieved better accuracy.
If some modifications are conducted to the second-order models
by removing some quadratic terms from plane and height for
reducing their correlation, the number of GCP required by the
geometric model could be less while maintaining comparable
accuracy. The positioning accuracy has been achieved with the
plane direction 0.7 meter and height direction 0.6 meter in the
sample spots of the whole test region.
ACKNOWLEDGEMENT
The paper is substantially supported by National 863 High-tech
Project “Complicated Features’ Extraction and Analysis from
Central Districts in Metropolis”, ChangJiang Scholars Program,
Ministry of Education, PRC and Tongji University “985”
Project Sub-system “Integrated Monitoring for City Spatial
Information”. The author would like to thank ChangJiang
Scholars Dr. Ron., Li and Dr. Hongxing Sun for their
invaluable help.
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