The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. P art B5. Beijing 2008
Regarding to the laser scanning technology, the scope of the
utilization was further varied by the spread of the high-
precision 3-dimensional laser scanners for the middle and long
distance in the early 2000's and the study on this technology is
continuously performed in the areas of engineering works, the
road and the cultural properties, etc also.
By the way, seeing the trends of overseas studies related to this
study, the cliffs at south beach of San Francisco where the
geographical activities are comparatively active was monitored
as using the 3-dimensional laser scanner and the safety was
predicted, which was proved to be used as the data for
preparing the countermeasures against the later stormwind. And
as modeling the perforated slope with the 3-dimensional
scanning scheme, the possibility and the problem of the
utilization of ground laser scanner were presented.
And there was the study to interpretate the transform of the
cross section in the tunnel with ground laser scanning
technology, the utilization of ground laser scanning technology
in the analysis of geometric error in the tunnel structure was
used to be presented (Gosliga et al., 2006;Lam, 2006).
Accordingly, this study is purported to determine more exact
internal cross section of tunnel with the enormous quantities of
point data obtained by ground laser scanning scheme and to
develop the cross section management system in the tunnel
which can utilize it at the actual practices. And the flowchart of
study is like Figure 1.
Data processing
Registration
Georeferencing
Analysis of data
Analysis of point cloud data
.Analysis of point georeferencing data
Development of cross section management system
Application of point cloud data
Calculate overbreak and underbreak
difference between Laser scanning technology and
photogrammetry is each technology adopts active sensor and
passive sensor. Different sensors support different way of
getting and processing information as well as the form of
information. TLSs allows a large amount of three-dimensional
data including colors and intensity information and their rapid
process.
TLSs operate on one of three principles: time-of-flight, phase
shift, or triangulation. A proper scanner for general use of large
scale applications is time-of-flight or phase shift methods using
timed pulse (Mills and Barber 2004). Triangulation scanners are
mainly used to close scan for cultural property restoration,
inspection, and reverse engineering fields.
Since this study has selected longitudinally long range highway
as a target, time-of-flight type scanners with relatively long
observation length were used. The Transmitted and received
signals are shown in Figure 2.
Amplitude
0 —*
Tr
ïi h
HU
1
L
h p
M
Sr
At
Sr (a)Transimitted signal
.Ltlil
Sn (b)Received signal Sr
Figure 2. Principle of distance survey using transmitted and
received signals in the TOF method
As shown in Figure 3, registration is a process that calculates
point clouds from different positions, which is calculating
relative positions that makes the gap between configurationally
common parts close to zero theoretically.
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Sub-project 1
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Sub-project 2
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o
Registration
Figure 3. Principle of registrating point clouds data measured
from different locations
Figure 1. Flow chart of study process
2. TERRESTRIAL LASER SCANNING TECHNOLOGY
The advantages of laser scanning compared to existing
techniques systems from the high rate-of-capture and density of
three dimensional data (Boehler et al. 2001). The greatest
This is the procedure of point clouds’ coordinate conversion to
form the same coordinate system, and it is determined by
movement and rotation elements in three-dimensional space.
The point clouds that have formed the same coordinate system
through registration is converted to target’s absolute coordinate
merging with control point by georeferencing as shown in
Figure 4.
