Monitoring Method of Landslide Using Laser Scanner-Accurate Geometric Transformation by Multi Surfaces MeasurementKazu KINOSHITA* Tomonori MIYAZAKI** Masataka TAKAGI***Infrastructure Systems Engineering, Kochi University of Technology
ABSTRACT: A landslide gives the big loss to various structures. However, a detailed mechanism of alandslide is not understood completely. Ground based laser scanner is expected as useful measurement
equipment for monitoring landslide. However, there are some problems in accurate measurement using theground based laser scanner. Laser scanner data must be transformed into the ground coordinates using
Ground Control Points (GCP). The prism is usually used for GCP. The ground coordinate of the prism isprecisely measured by using GPS and Total station. However the acquisition of accurate coordinate of theprism in laser scanner data is very difficult. The error of the transformation showed maximum 10cm.
This study focused on solving the problem in the geometric transformation. The accurate measurement ofcontrol points can be improved by measuring some flat surfaces. When three flat surfaces are measured,
coordinates of the intersection in three planes can be calculated. This intersection can be used as a control
point of the laser scanner data. This method should make accurate geometric transformation. Geometrictransformation by using multi surface measurement was higher accuracy than geometric transformation
using a prism. And, accuracy of geometric transformation showed less than 1cm.

1. BACKGROUND
1.1 The current landslide observationequipment for monitoring landslide. Laser scanner

A landslide is a phenomenon of mass movement onwide

the ground, which moves 0.01mm 10mm/day in thedisplacement by using laser scanner, less than 1cm

wide area. There are various inducements of aaccuracy is required.

can acquire three-dimensional data in a short time, inarea.

Fortheextraction

oflandslide

landslide such as geology, topography, soil andhydrology.

Current

landslidearemonitoring

using

boreholesystems

ofainclinometer,

1.3 Problem in Accurate measurement
using A Laser Scannerextensometer or GPS. Borehole inclinometer can

1.3.1

Accurate Measurement

measure the angle of the guide pipe by using strain

Figure1-1 showed Digital Surface Model(DSM) ofmeter. Extensometer can measure the amount ofsmooth flat board which was measured by laser

expansion and contraction between two points. GPS

scanner in 20m measurement distances. The DSM

is used for point measurement. Those monitoring

was represented contour line with Triangulated

systems for detection landslide displacement canIrregular Network, which was given shading for easymeasure at some points or along lines. It is difficult

understanding. In the DSM, measured points seemedto measure whole landslide area by current systems.

rough surface including random error. Therefore, thenoise reduction system should be developed for

1.2 Laser Scanner Measurement
Laser scanner is expected as useful measurement

accurate measurement.

Total station. The location of the prism in laser
scannerdataareextracted

automaticallyby

reflection strength of the prism by with bundle
software of laser scanner. However, coordinates of
the control points in laser scanner data cannot beaccurately extracted. When control points have someerrors,

precisionofgeometrictransformation

becomes low accuracy. Therefore, acquisition of thecontrol point coordinates becomes important.

1.4 Experiment in landslide field
In Shikoku, Japan, there are four big active faults.
Many landslides are occurred along the active faults.
Now, landslide prevention areas exist over 1,500
places in Shikoku, Japan. In this study, test area wasselected Chouja landslide in kochi pref. In Chouja,
width of landslide is about 200m, length is about
900m and average slope is about 15 degrees. It is
Figure1-1 Sample of Laser Scanner data incase 20m distanceone of the biggest landslides in Japan. Figure1-2
showed Arial photograph of Choja landslide.

1.3.2 Accurate setting
When displacement of a landslide is measured byusing portable laser scanner, time series data areneeded. Then the laser scanner must be set
repeatedly at same point. It is difficult to set
accurately at same point in each observation. The
position of laser scanner in horizontal plane can be
adjusted by centering equipment. However, it isdifficult to set in vertical axis by using tripod. In
addition, starting point for scanning is not always
same point. Because, telescope for collimation is notmounted on the laser scanner.

1.3.3 Accurate control points in laser scanner
dataLaser scanner data must be converted into theFigure 1-2 Choja landslide

ground coordinate using Ground Control Points. Aprism is usually used as GCP. The ground coordinate

1.4.1 Specification of Used Laser Scannerof prism can be precisely measured by using GPS or

In this study, LMS-Z210 produced by Riegl wasused as laser scanner. Maximum measurement range

Table 1-2.Specification of laser scannerby the laser scanner is 350m. Accuracy is about 2.5
centimeter in standard deviation. Table 1-1 shows
Performances of measurement distance. Table 1-2
shows specification of Laser scanner.

Frame scanLine scan

Pixel(max)1106 pixels

4621 pixels

Angle Range±40°

0°～333°

Pixel(max)

1106

Angle

0.036°

0.018°

resolution(actual 0.072°)(actual 0.072°)

pixels4621

pixels

1.4.2 Measurement Result Using Prism
In the observation, 5 prisms were set up and scanned
8 times. Table 1-3 shows acquisition precision of acontrol point which extracted automatically bybundle software. Standard deviation of control point
coordinates

werecalculated

from8times

measurement. The coordinates of the same control
point have 10 cm error in maximum. It was very bigerror comparing with laser range accuracy (2.5cm).
Table 1-4 shows Root
Figure 1-3 Laser scanner

Mean

SquareError ofgeometric transformations by using prism. GCP wasmeasured by Total Station (3mm accuracy). The
geometric transformation is low accuracy that it isTable 1-1.Performances of measurement

difficult to detect the landslide displacement incurrent condition.

Range

≦350m
(reflectance≧80% of objects)

Range

≦150m

Table 1-3 Standard deviation of a coordinateof a prism(reflectance≧10% of objects)

Shortest

2m

Distance
Measurement±2.5cm

Accuracy(Standard Deviation)

Laser

0.9μm

Wavelength(Infrared)

xc(m)
yc(m)
zc(m)
prism1 1.25E-01 3.52E-02 1.75E-02
prism2 5.94E-02 8.53E-02 9.82E-03
prism3 4.57E-03 7.90E-02 5.99E-03
prism4 8.51E-03 3.28E-02 3.16E-03
prism5 1.00E-01 5.43E-02 1.98E-02

Table 1-4 R.M.S.error (m) of geometrictransformation

scan number
scan1
scan2
scan3
scan4
scan5
scan6
scan7
scan8

Prism
5.52E-02
2.02E-02
5.54E-02
5.87E-02
7.10E-02
2.54E-02
5.07E-02
3.33E-02

Following equations show estimated error of
coordinates in standard deviation by low of error
propagation. The error of an angle was assigned 1/10of angle resolution in laser scanner.

2. OBJECTIVESThis study is focusing on solving the problem in theacquisition of the accurate control points. Point
measurement is very difficult by laser scanner
because of no collimation telescope. The accurate
measurement can be carried out by surface
measurement. When three surfaces are measured,

3.1 Measurement Objectcoordinates of the intersection with three surfaces

The measurement object must be a flat surface. So

can be calculated. This intersection can be used as

the two kind of flat boards were prepared as flat

control points of the laser coordinates. Objectives ofsurface. The board’s size was 1.37*1.525m, andthis study are acquisition of accurate control points

1.20*1.65m. The 3 boards were set up for one

in laser scanner data by multi surface measurement

control point (Figure 3-1). Figure 3-2 shows location

andlandslideof measurement board. Test area was divided into 4

monitoring is required less than 1cm in standard

blocks. There were 3 boards in each block. Laser

deviation.

scanner measurements were repeated 8 times intheevaluation.
Therefore,Accuracy
accuracy

forofgeometrictransformation should be also less than 1cm.

same condition.

3. Method for Measurement ofAccurate Ground Control Points
The coordinates of the target by laser scanner iscalculated by following equations.

Figure 3-1 Picture of measurement board

Table 4-1 shows estimated error and result ofexperiment. Result of experiment shows higher
accuracy than estimated error.
Figure 3-2 Location in test area

Table 4-1 Error in plane equation

board1
board2
board3

estimated error
error of experimentabcabc
2.77E-03 5.26E-03 2.79E-03 8.30E-05 1.55E-05 9.06E-05
8.24E-03 2.14E-03 2.64E-03 1.22E-04 3.69E-05 9.96E-05
6.90E-03 6.19E-03 5.69E-02 1.17E-04 4.59E-05 2.14E-04

4. METHOD FOR ACCURATECONTROL POINT
4.1 Establishing Equation of Planes inLaser Coordinates

4.2 Intersection Point by Three Planes asVirtual GCPs

The derived equation of plane will be accurate

Coordinate of intersection can be calculated using

position of the surface. Following equation isthree equations of planes by following equation.

equation of plane in three dimensions.

The equation of plane can be derived using manymeasurement points by least square method. Numberof measurement point will influence to accuracy ofthe derived equation. The unknown coefficient canbe calculated by following equation.
Estimated error of coordinate of intersection can becalculated following equation.

Estimated error can be also calculated by low ofTable 4-2 shows estimated error and result oferror propagation as follows;

experiment in coordinates of intersection. The error

of coordinates of in the experiment has maximum 2

intersection of three planes, precision showed higher

cm in Z-axis. Because value of Z-coordinate inaccuracy that error showed less than 1.0 cm.

control point was almost same in each block. Then
accuracy in Z-axis might be lower.

5. CONCLUSIONS
Table 4-2 Acquisition precision of aGeometricreference point by three planesmeasurement was higher accuracy than geometric

Block1
Block2Block3Block4

estimated error
xc(m)
yc(m)
zc(m)
5.20E-02 5.09E-02 2.86E-02
9.47E-03 5.64E-03 5.26E-03
9.91E-03 3.15E-03 5.39E-03
5.02E-02 4.24E-02 2.49E-02

error of experiment
xc(m)
yc(m)
zc(m)
4.40E-03 6.08E-03 1.15E-02
4.08E-03 1.97E-03 5.73E-03
4.04E-03 1.43E-03 2.67E-03
3.93E-03 7.97E-03 1.80E-02

3 dimensional affine transformation was applied
for geometric transformation as follows;transformation

bymultisurfaces

transformation by a prism. And, the accuracy ofR.M.S.Error showed less than 1cm. However theresult of estimated error showed lower thanexperiment. The estimation by low of error
propagation is checking now. Movement of alandslide should be detected by surface measurement.
This method is difficult to set up twelve boards on
the landslide area. Portable multi surface boards
should be made in near future.

6. REFERENCES
Tomoya SAKAI, Jong Hyeok JEONG andGCP was measured by Total Station (standardMasataka TAKAGI, Laser Scanner Measurement fordeviation 3mm). The reflector sheets which put at

Monitoring Landslide Dispacement, Proceedings ofthe corner on the board was measured by Total

the 26th Asian Conference on Remote Sensing,Station. Equation of plane and the intersection was

Hanoi VIETNAM, pp.LID2-2, 2005

calculated as well as laser scanner data. Table 4-3
shows R.M.S.error of geometric transformations by

Jaan-Rong Tsay・Shu-yi Lee, Corner Features forusing prism, and by using the intersection of three

Unifying Coordinate Systems of Multiple LIDAR

planes.

Stations, Proceedings of the 26th Asian Conferenceon Remote Sensing, Hanoi VIETNAM, pp.LID1-5,

Table 4-3 R.M.S.error (m) of geometric2005

transformation

scan number
scan1
scan2
scan3
scan4
scan5
scan6
scan7
scan8

Prism
2.64E-02
1.36E-01
5.61E-02
9.75E-02
5.61E-02
1.01E-01
8.42E-02
1.31E-01

Intersection
7.48E-03
8.85E-03
8.39E-03
7.70E-03
1.11E-02
7.96E-03
7.28E-03
9.17E-03

As for the geometric transformation by the

Jaan-Rong Tsay, A Concept and Algorithm For 3D
City Surface Modeling, ISPRS Commission III,Symposium 2002
RIEGL Japan. Ltd., ”LMS-Z210 owner’s manual”