The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B5. Beijing 2008 
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center line of road are automatically abstracted. The point data 
of the cross section abstracted like that are linked with the 
lowest square line by the principle of the lowest square and 
Figure 17 shows the figures which automatically abstracted the 
cross section of concerned tunnel at intervals of 1.0m 
The cross sections abstracted like that are converted into DXF 
format to be stored like Figure 18 and the final cross section is 
determined after passing through the correction step under the 
CAD environment. Figure 19. shows the random cross section 
of the tunnel passing through the final correction step. 
Figure 17. View of extracting cross section at intervals of lm 
by profile/cross section tool 
Figure 18. View of DXF format at CAD interface 
3.3 Analysis of results 
Prior to determining the internal corss section as using the scan 
data treated over the whole cross sections, the accuracy of 
dimensions by the number of measuring points for determining 
the section was analyzed. The laser scanning scheme used in 
this study can observe over minimal 500 measuring points at 
the random cross sections. Accordingly, the sectional 
dimensions determined by 15-25 and 50 measuring points 
which are generally applied for the sectional measurement of 
tunnel and the sectional dimensions by the laser scanning 
scheme were compared. The Table 5 is to compare the sectional 
dimensions of each cross section and the average sectional 
dimensions by the number of measuring point at the sectional 
intervals of 1.0m at STA.17+800~STA.17+810. 
points 
STA. 
Area of a cross section (m 2 ) 
>500 
50 
25 
15 
17+800 
88.96 
88.76 
86.15 
85.75 
17+801 
87.05 
86.67 
85.68 
85.24 
17+802 
88.25 
87.74 
86.87 
86.05 
17+803 
88.54 
88.15 
87.56 
87.01 
17+804 
88.78 
87.87 
87.12 
86.88 
17+805 
89.87 
89.35 
88.89 
87.89 
17+806 
89.25 
88.74 
88.51 
87.78 
17+807 
89.58 
88.94 
88.48 
87.89 
17+808 
89.28 
88.87 
87.92 
87.18 
17+809 
88.85 
88.25 
87.70 
87.08 
17+810 
89.35 
88.77 
88.05 
87.43 
Average 
88.89 
88.37 
87.54 
86.93 
Table 5. Area of a cross section classified the number of points 
Comparing these results with the standard sectional dimensions 
of 91.58m 2 is like Figure 20. In the case by the laser scanning 
scheme, there was the smallest difference of about 2.9% from 
the standard sectional dimensions. In case that 15 measuring 
points were applied, there was the biggest difference of about 
5.1%. Like the above, in case of determining the random 
section as using the laser scanning scheme, the accuracy of 
dimensions was appeared to be improved by 0.6%, 1.1% and 
2.2%, respectively as compared with the section determined by 
the number of measuring points of 50, 25 and 15. This, 
although there is the smallest difference in a section, means that 
there is very big difference in considering the whole length. 
Excavation 
93.5% L ■' 
>500 50 25 15 
No. point(EA) 
Figure 20. Distribution chart of each excavation classified the 
number of points 
The results comparing outbreak quantity and underbreak 
quantity by the interval of random cross section showed the 
distribution like Figure 21. In the excavation of tunnel, the 
underbreaks have many effects on the constructing period as