The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part BI. Beijing 2008 
24 
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Figure 9. DMC50 collocation grid vs. PATB grid 
x 10 
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6.16 6.165 6.17 6.175 6.18 6.185 6.19 
x 10 S 
Figure 10. Mean DTM trend difference, max=0.04[m] 
ISAT vs. BLUH 
Photo-T : Collocation Grid 
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Figure 11. DMC50 collocation grid vs. BLUH grid 
Figure 12. Mean DTM trend difference, max=0.03[m] 
ISAT vs. BINGO (Typical Model) 
As one can see from Figures 8-12, the maximum DTM trends in 
Z between ISAT collocation and three self-calibration bundle 
adjustment programs differ by about only 4 cm, which is within 
the error range on check points; thus, they have the same 
accuracy within precision of the method. However, the 
systematic grid pattern in image space that has led to almost 
identical block shape in object space is quite different between 
the methods. In total, the maximal difference between two 
grids (collocation and self-calibration) is equal to 5[um], which 
means that self-calibration overcorrects (on the edges) almost a 
half pixel. Since collocation grid represents true residual trend 
in image space, the difference between any of self-calibration 
grids and collocation grid is the amount of true systematic 
distortion left in image space after self-calibration grid 
refinement. So, the price to pay for correcting the block 
geometry in object space using self-calibration grid is to have 
significant systematic error in image space, possibly even larger 
than the initial systematic error. Such overcorrection at the 
edges may pose significant problems for assembly of ortho 
mosaics, and definitely the VIR grid correction in DMC PPS 
derived from self-calibration does not provide “distortion-free” 
images. 
6. CONCLUSIONS AND FUTURE WORK 
Six DMC cameras have been calibrated for VIR correction grid 
using the collocation method. In this paper, the DMC50 block 
has been used to compare several self-calibration grids to the 
collocation grid. Test sub-blocks of different configurations 
(regular 60/30 layout of 38 photos, 60/60 layout of 89 photos, 
and the whole calibration block of 1105 photos with 60/80 
layout) have been used to measure the effect of DTM 
unbending by application of a VIR correction grid. The most 
reliable estimate of the unbending effect is the mean DTM trend 
difference between a GPS-constrained test block and 
unconstrained test block (sparse control at the edges of the 
block). This configuration produces the maximal block bending, 
and the mean DTM trend difference (and its maximum) serves 
as a robust estimate of the improvement in DTM shape. The 
robustly-computed mean trend is free from the effects of local 
deformation affecting sparsely distributed check points. The 
total attenuation of DTM bending on a sub-block selected from 
the calibration block ranges 2-4 times. The expected attenuation 
for any other block (flown at a different GSD) is about 2 times