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The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B5. Beijing 2008
INSTUMENT
/SOFTWARE
PROCESS
Main RESULTS
RTK-
GPS
ASHTECHZ-
12/Trimble40
OOsse
Selected the main
inflexion and change-
point of the MGWand
surveyed 58 GPS points
by the RTK-GPS
It is difficult to select
GPS point to describe the
MGW and to reach some
points such as the watch
towers and to set the
tripod.RTK-GPS is not
suitable for measuring
the MGW
Photo
gram
metry
VirtuoZo
1:8000 aerial photos, 22
stereo pairs, 1:10k control
points
under the stereo model, it
is easy to select the
points to measure the
MGWand the operation
is reproduced with the
support of the theory
1:50k
DRG
and
DEM
Arcgis
Digitizing the MGW
elements based on DRG ,
getting X,Y from the
DRG and Z from the
DEM
The MGW elements of
the DRG is being
synthesized during the
map compilation. The
precision of the 1:50k
DRG and DEM can not
meet the need of the
MGW resource
investigation. Using
1:50k DRG and DEM is
not suitable for
measuring the wall
Table 1. The Comparison of the Main Measuring Ways
PROJRCTION LENGTH
SURFUCE
LENGTH
RTK-GPS (LI)
2309.93
2445.25
PHOTOGRAMMTRY(L2)
2359.09
2481.64
L1-L2
-49.16
-36.39
(L1-L2)/L1
-2.13%
-1.49%
Table 2. The Length Comparison Between RTK-GPS and
Photogrammetry
The chart shows the difference by comparing RTK-GPS and
photogrammetry, the result proves the use of RTK-GPS to
survey the length of the MGW is not feasible.
Figure 5. The Comparison Between RTK-GPS and
Photogrammetry
The test result shows that the Photogrammetry is the best way to
measure the slope length of the MGW.
5.2 1:10k Specification Precision
In order to compare the impact on the length using different
scale aerial images to measure the same section of the MGW,
the pilot uses respectively 1:8000 and 1:35000 scale aerial
photos to measure two categories of the MGW (plain and
mountain type) according to the Specifications for aero
photogrammetric office operation 1:10k topographic maps, the
test results in table 3.
1:8000( LI )
1:35000 (L2 )
LI- L2
(LI- L2) /LI
Mountain
3,300.19
3,302.02
-1.83
1 /1803
Plain
2,495.37
2,493.56
1.81
1 / 1379
Table 3. The Surface Length Comparison Between 1:8000 and
1:35000 Scale
Table 3 shows the differences between the two kinds of aerial
scale (1:8000 and 1:35000) measuring the surface length of the
MGW based on the different terrain conditions
By analyzing the results of the trial, the measuring length’s
difference of the two scales relative to the length can basically
ignored, the MGW length measurement accuracy mainly
depends on the specification’s accuracy indicators rather than
the scale of the Aerial photos, but large-scale aerial photos of
the MGW can improve the identification and measurement
capability.
Figure 6. Exiting Air-photos Statistics Covering The MGW
The figure6 shows the scale series of aerial photos covering the
district of the MGW mainly focused on the scope of 1:25000 to
1:35000.
To make full use of existing aerial photos, the Specifications for
aero photogrammetric 1:10k topographic maps eventually has
been determined to measure the length of the MGW on basis of
trial.
5.3 Length Measurement Precision Test
The test had been done in the Beijing Badaling section of MGW
(mountain type, about 2.5 kilometers), densification points
(mountain type) plane mean square error is 5.0 meter, elevation
mean square error is 2.0 meter, the calculating surface length
accuracy of the MGW is ± 19.37 meter according to the
accuracy evaluation formula(2).
Provided that the total length of the MGW were 5,000 km, the
total measuring times were 2000 and the each section’s
measuring accuracy were the same as the above test’s accuracy,
the expected length measurement accuracy of the MGW can be
achieved ± 0.866km.
6. CONCLUSIONS
This paper discussed the measurement method of the MGW
based on image, which is to Interpret and identify the
elementary distribution of the MGW based on ortho-image
