International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B3. Istanbul 2004 
  
2.2 Image data 
Evaluated images are ‘QuickBird panchromatic basic imagery” 
with a radiometric correction and a sensor characteristic 
correction. The observation date of images is April 22, 2003 
and their ground resolution is 0.78m. The area of each image is 
450km? (21.2km*21.2km). The off-nadir angle of the forward 
view is 28.7 degree and that of the backward view is 27.2 
degree. The overlap is about 9096. 
2.3 3D model 
The evaluated 3D model is an RPC model by using parameters 
distributed with images. 
2.4 Image measurement 
The 60 check points were selected from obvious objects in 
images (e.g.. an intersection of lines at parking lot, Fig. 3). 
Then 3 dimensional coordinates are measured on the 3D model 
by stereoscoping at a digital photogrammetry software. Each 
point is measured twice and calculated the average as the 
coordinates A. The standard deviation of the differences 
between the two measurements is 0.19m in easting, 0.15m in 
northing and 0.23m in vertical. 
3 
   
Fig. 3 An example of check points 
(Left: forward-view, Right: backward-view) 
2.5 GPS survey 
The check points were also surveyed by fast-static GPS (Fig. 4) 
and coordinates B were obtained. The reference station is one 
of permanent GPS stations of the GEONET (GPS Earth 
Observation Network of the GSI, Hatanaka et al, 2003). The 
observation time of each point is 30 minutes and PDOP of each 
observation is less than 6. 
  
    
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©2004DigitalGlobe. 
2.6 Evaluation of horizontal spatial accuracy 
The horizontal component of error vectors (coordinates A — 
coordinates B) are indicated in Fig. 5. 
An apparent westbound shift is observed at all points. The 
average of the easting component of the shifts is 13.13 m and 
that of the northing component is 2.78m. The standard 
deviation of the easting component is 0.73 m and that of the 
northing component is 0.93 m. 
  
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10m 
  
  
  
  
Fig.5 Horizontal component of error vectors 
Since all vectors have the same tendency, we tried to correct 
the shifts by fixing one point as a ground control point 
(GCP). Fig. 6 shows a correction result in which the center 
point of images is used as a GCP. The average of the easting 
component of shifts decreased to 0.74m and that of the 
northing component decreased to 0.79m. 
  
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Fig.6 Horizontal component of error vectors 
(after correction) 
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