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Thus, as in the quantitative evaluation, the stereo models of the 
previous and following strips are judged to be the best 
combination for the RPM from the viewpoint of processing cost. 
3.2.2.2 Comparison of the restricted application of the 
RPM in the coarse-to-fine approach 
For the RPM using stereo models of the previous and following 
strips, changes in the accuracy of the DEM are examined based 
on the restricted application of the RPM in the coarse-to-fine 
approach. The qualitative evaluation of the DEM accuracy is 
performed by checking the distribution of mismatched points on 
the color-shaded maps. 
Figure 7 shows the changes in the color-shaded maps for arcas 
A and B, with variations in the restricted use of the RPM in the 
coarse-to-fine approach. 
Figures 7(a) and 7(b) show color-shaded maps for mountainous 
arcas and rice fields, respectively. Mismatched points are 
generated in the squared areas without the use of the RPM. 
Additionally, it was confirmed that these mismatched points are 
removed for both areas when (1) the RPM is used with all 
resolution stages, (3) the RPM is used with a high-resolution 
stage, and (4) the RPM is used with DTM as a reference. 
Ortho W/O 
Photo RPM (1) @) (3) (4) 
  
(a) Mountain (area A). 
Aero photo by GSI Japan (2008) 
    
  
  
    
0 200m (b) Rice fields (areaB) 
Figure 7 Comparison of elevation with the 
RPM Changing Resolution Stage in coarse-to-fine approach 
Here, as in the quantitative evaluation, from the qualitative 
evaluation of the restricted application of the RPM, it was 
confirmed that these same cases improve the accuracy of the 
DEM. Based on the processing time for cach case shown in 
Table 6, from a qualitative examination, it was judged that (4) 
the RPM with DTM as a reference using only high-resolution 
stages in the coarse-to-fine approach is the most applicable 
method. 
3.3 Examination 
In this section, changes in the accuracy of the DEM are 
examined, with variations in the stereo model combinations for 
the RPM, and with variations in the application of the RPM in 
the coarse-to-fine approach. 
3.3.1 Changing the stereo model combinations for the RPM 
From the quantitative and qualitative evaluations in section 3.2, 
the accuracy of the DEM was confirmed to be better when the 
RPM is used with all stereo models, or with only stereo models 
of the previous and following strips, as compared with stereo 
models of only the current strip. 
This result is speculated to have been caused from changes in 
the usable area of the projection based on variations in the 
stereo model combinations for the RPM, as the RPM, from its 
mechanization, cannot evaluate the reliability of the matched 
points when there is no stereo model to project, and because the 
reliability of the matched points depends on the amount of 
usable area for the projection. 
Table 7 shows the amount of usable area for the RPM and the 
reduction in the number of mismatched points for area D, where 
aerial photos are taken under the normal condition of a 60% 
overlap and 30% sidelap. It was confirmed that the amount of 
usable area for the RPM is proportionally related with the 
reduction in the number of mismatched points. 
  
  
  
  
  
  
# of Mismatched #of Rates of 
Usable 
area pts. in usable area reduced reduced 
(96) W/O With mismatch | mismatch 
2 RPM | RPM ed pts. ed pts 
All Stereo 0 
Model 78.0 121 90 31 25.6% 
CUR Strip 43.0 38 34 4 11.8% 
PREV and o 
FF Strips 58.2 105 78 27 25.7% 
  
  
  
  
  
  
Table7 Amount of usable area for the RPM and 
the reduction in the number of mismatched points ( Area D ) 
From this result, the reduction in the number of mismatched 
points is the highest when the RPM is used with all stereo 
models. However, a few gaps exist in the rate of reduction of 
mismatched points when comparing the use of the RPM with all 
stereo models and with stereo models of only the previous and 
following strips. In addition, based on the processing cost with 
an increasing number of stereo models for the RPM, it was 
determined that the use of the RPM with the stereo models of 
the previous and following strips is the most effective method. 
3.3.7 Restriction of the RPM in the coarse-to-fine approach 
From the evaluation described in section 3.2, it was confirmed 
that the RPM with a restriction in the high-resolution stages in 
the coarse-to-fine approach, and the RPM using the DTM as a 
reference, both improved the accuracy. Figure 8 shows the 
changes in the color-shaded maps under the coarse-to-fine 
approach for each use of the RPM. From this figure, it can be 
confirmed that the mismatched points generated in the square 
areas are not filtered during the resolution stage when the RPM 
is not used. 
Furthermore, when the RPM is used with DTM as a reference 
during the lowest-resolution stage, large mismatched points are 
removed during stage 4 prior to the matching process during the 
higher resolution stage. Therefore, it is speculated that 
unnecessary searches are prevented and that the processing time 
is drastically reduced. 
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