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3. RESULTS AND EXAMINATION 
In this chapter, to confirm the effectiveness of the RPM 
proposed in this research, a DEM is extracted from aerial photo 
images using a matching process, and then qualitatively and 
quantitatively evaluated. 
3.1 Various Factors 
The aerial photo images used for the examination in this 
research were taken over five different areas. Each of these 
areas contains mountains, which are easily mismatched. The 
aerial photo images were also taken under the conditions shown 
in Table 1. When analog cameras were used, digital image files 
were created from the film using the pixel sizes shown in this 
table. 
Here, the theoretical values for the horizontal (oy) and vertical 
(079) directions are induced from parallax equation (2). where 
oxy is the theoretical value for horizontal accuracy; oy, the 
theoretical value for vertical accuracy; H, the height to ground; f, 
the focal length; B, the baseline length; and op, the Read Delta 
(1.0 pixel in this research). 
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
H HH 
Oxyo = 7 92 C= 656, (2) 
Focal Pixel 
Area Features Camera Length Size 
(mm) (um) 
A Mountains * Forests DMC 120.00 12 
B Mountains * Rice Fields RC30 153.32 20 
C Mountains * Rice Fields RC30 152.94 20 
D Mountains * Urban DMC 120.00 12 
E Mountains* Urban RC30 213.90 20 
Photo OL SL Theoretical Value 
Area Scal E a Horizontal Vertical 
cale (%) (%) 
(m) (m) 
A 1:16,000 60 50 0.194 0.953 
B 1:15,000 60 50 0.277 0.748 
C 1:12,000 70 50 0.273 1.090 
D 1:16,000 60 30 0.207 1.025 
E 1:12,500 60 30 0.253 0.864 
  
  
  
  
  
  
  
  
Table 1 Various factors of the Aerial Photos 
3.2 Accuracy Estimation 
In this section, for an examination of the improvement in 
accuracy of the DEM extracted from an aerial photograph when 
applying the RPM, quantitative and qualitative evaluations are 
first performed. 
Next, from a fear of expanding the processing cost of the RPM, 
as an increasing number of stereo models are used, the best 
combination of accuracy and processing cost was determined by 
adapting the stereo models for use with the RPM, as shown in 
Figure 4: (a) all stereo models of neighbors of the master image, 
(b) stereo models in the current strip, and (c) stereo models in 
the previous and following strips. 
Furthermore, under the best combination of stereo models, the 
restriction of the application of the RPM in coarse-to-fine 
approach is varied as shown in Figure 5. Here, the RPM is 
performed for (1) all resolution stages, (2) low-resolution stages 
only, (3) high-resolution stages only, and (4) with the DTM as a 
reference in the lowest-resolution stage and the RPM in the 
high-resolution stages only. In addition, the best method is 
investigated from by comparing the accuracy and processing 
time. 
  
(b) CUR strip (c) PREV and FF Strips 
Figure 4 Combination of the stereo models for use of the RPM 
    
Step6 StepS Step4 Step3 Step2 Step | 
  
  
  
(1) < RP 7 
(2) + » « » 
RPM W/O RPM 
dal A d. a 
GS W/ORPM = © RPM ch 
(4) 
DTM REF RPM 
Figure 5 Restriction of the application of RPM 
in coarse-to-fine approach. 
Aerial photo by GSI Japan (2008) 
3.2.1 Quantitative Evaluation 
A quantitative evaluation of the RPM is performed by 
calculating the elevation gap between the matched DEM and 
the airborne lidar data treated as the most probable value. The 
elevation gaps are calculated at the check points where the 
edges of the features on the digital ortho photographs can be 
clearly distinguished. 
Here, points with elevation gaps over the theoretical value for 
the vertical direction, as shown in Table l, are regarded as 
mismatched points.The airborne lidar data satisfies the accuracy 
of map level 2500, with a density of 2.8 points per square meter. 
3.2.1.1 Comparison of variations in the stereo model 
combinations for the RPM 
Based on the variations in the stereo model combinations for 
the RPM, the mean squares of the elevation gap change, as 
shown in Table 2, as do the number of mismatched points, as 
shown in Table 3. From Tables 2 and 3, for the RPM with all 
stereo models or with stereo models of the previous and 
following strips, it is confirmed that both the mean square of the 
elevation gap and the number of mismatched points are 
improved as compared to a case without the use of the RPM. 
Here, the gap in the value between the use of the RPM with all 
stereo models, and with the models of the previous and 
following strips, is slight. 
169