International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B7. Istanbul 2004
2.3 Modeling of Points Clouds
An explicit useful spatial dataset is achieved by jointing all
point clouds of multiple scans of a targeting object The vectors
can be projected onto a plan surface or transformed into a map,
or even to make a 3D perspective views.
2.4 Coordinate Transformation of Points Clouds
After joining all datasets into a single point cloud model with a
common coordinate system, a further step is to transform the
local coordinate systems into a geodetic system by using
ground control points measured by ground surveying, in this
study using GPS and Total Stations.
|
X x-X,
Y > Rens : = V
(X, Y. Z:) s = t
V X
A Scanner Coordinate System *
Objed Coordinate System — X
Figure 2.2. A sketch showing the coordinate transformations
of multi-scanning point clouds
3. RESULTS OF THE CHANGE DETECTION
In this study, ground-based 3D laser scanning is applied to two
cases. One is a river-side landslide in Chudong of Hsin-chu
County which is a typical and common one in Taiwan (Hsiao et
al., 2003a & 2003b). The other is the toe area of the large-scaled
dip-slope landslide of Jiu-fen-er mountain in central Taiwan.
3.1 The River-side Landslide Case
The Chudong landslide is located in a small valley with a very
limited open space for taking a good view of the whole area
(Figure 3.1). Six scanning stations with scanner-to-target
distances less than 100 m were applied.
Figure 3.1. The area covered by ground-based lidar with 6
stations.
The extent of a scanning station and the point spacing as well as
the duration required for a scan are displayed on the PDA
controlled panel of the scanner ILRIS-3D. Six datasets
generated by six scanning stations are subsequently merged into
one single dataset. And, then, a coordinate transformation was
conducted by using six control points distributed in the area and
measured by GPS (Figure 3.1). Thus, a useful topographic
model is established. Figure 3.2 shows the application of a 2D
plane map and a 3D perspective map.
For understanding the topographic change of the landslide area,
an existing topographic map in a scale of 1:5000 was digitized
to obtain the topography before the sliding event. Though no
other more detailed topographic information could be accessed
for the study area, the most common topographic information of
the 5K photomaps are useful for a quick understanding of the
618
landform evolution of the study area. As shown in Figure 3.3,
the topographic information from 5K topographic maps and that
from laser scan are compared to obtain the altitude variation. A
volume change with obvious spatial variations indicates a
significant result can be achieved by this approach. The
estimated change of earth volume is 11,691 m? with a landfill of
4,899 m? and a cut of 6,792 m°.
Additional information, a merit in contrast to the traditional
topographic survey, is the portrait of detailed profiles of the
landslide using the densely distributed data points, as shown in
Figure 3.4.
(a) 2D plane map (b) 3D perspective map
Figure 3.2. 2D plane and 3D perspective maps after
modeling of points cloud data
(a) 5 profile map
(b) A profile altitude |(c) B profile altitude
N
VEI ; L4 mms er ;
ru HE S SO ; iS.
(d) C profile altitude. | (e) D profile altitude | (f) E profile altitude
Figure 3.4. Profiles of the Chudong landslide
32 The Jiu-fen-er Slide Area
The most common digital terrain information in Taiwan is the
DTM with a 40 m grid. Another most common topographic
information is the 5K photomaps. Another datasets for this area
is the point clouds taken by airborne lidar (Shih et al, 2002).
Stereo-pairs of aerial photographs of the area are used to
generate | m contour interval topography. Figures 3.5 and 3.6
are the study area and its DEM modeling. Figure 3.7 is a 3D
perspective view generated by from SPOT image and 40m
DTM. Figure 3.8 shows the topography before and after the
Ji-Ji Earthquake. A dramatic change of topography can be
perceived.
Airborne lidars of Optech ALTM 2030 and LH ALS40 were
introduced to Taiwan by Agriculture Council for taking test
Inter
datas
2002
were
lidar
In su
been
of th
show
post-
taken
Figut
airbo