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The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B4. Beijing 2008 
cos S = sin or, sin a 2 + cos a, cos a 2 cos(0 2 - Of (7) 
where & is the convergent angle, a ‘ and ( 1 = ^ ) are the 
nominal azimuth and elevation angles, respectively. The 
location of QuickBird imagery when taking images was 
illustrated in Figure 1. Some information regarding the images 
are shown in table 1, including data, time, view angle, off nadir 
angle, pixel resolution. DigitalGlobe has provided both the 
panchromatic and multispectral imagery with resolution of 0.7 
meter and 2.8 meters respectively. The two panchromatic ones 
with resolution of 0.682 m and 0.717 m were chosen as the test 
images due to their high resolution and convenience for 
measuring the GCPs of GPS survey. 
Left Image 
Right Image 
Acquisition Date 
15 Feb 2004 
5 May 2004 
Acquisition Time 
02:30:28 
02:26:18 
Scan Direction 
Forward 
Forward 
Image Size (pixels*pixels) 
27552 x 25776 
27552 x 25952 
Along-Track View Angle (°) 
19.8 
14.6 
Cross-Track View Angle (°) 
-5.5 
19.6 
Off Nadir View Angle (°) 
20.6 
24.4 
Pixel Resolution (m) 
0.682 
0.717 
Satellite Azimuth Angle (°) 
353.9 
60.4 
Satellite Elevation Angle (°) 
68.2 
64.0 
Convergent Angle (°) 
25.9 
Figure 1. Location of QuickBird Imagery when taking images 
3.2 GCPs Collection 
The high accuracy GCPs were obtained by GPS field survey in 
Shanghai urban area. The imagery obtained by DigitalGlobe 
was raw data without any geometric correction, thus distortion 
existed compared with topographic map and hard for GCP 
selection. The initial geometric correction was performed 
remote sensing software ERDAS and GIS software Emap- 
information developed by Emap Corporation. The field survey 
was issued with the aid of Shanghai Virtual Reference Station 
(VRS) provided by Shanghai Surveying and Mapping Institute. 
There were two types of GPS survey points considering the low 
Table 1. Some Information of QuickBird Across-track Stereo 
Imagery 
relief in Shanghai urban area, the ground GPS survey and the 
building roof GPS survey. In general, the whole area was 
divided into 7*7=49 small survey districts. Each survey district 
was selected at least one GCP for the ground GPS survey 
according to concrete conditions, and totally 179 points were 
obtained in this type. 20 building roof GPS survey points were 
collected from different buildings whose height ranges from 30 
to 420 m. The RMSE for the GPS survey points was 0.05 m. 
The initial geometric correction pair and distribution of GPS 
survey points and districts are illustrated in Figure 2 
(a) 
(b) 
Figure 2. The QuickBird across-track stereo imagery and the distribution of GPS survey points, (a) left (Feb) image of the stereo 
pair, (b) right (May) image of the stereo pair. The red triangles represent the ground GPS survey points, the yellows ones the 
building roof survey points. The green rectangles are the 49 districts designed for selection of GPS survey points. 
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