Terrestrial Laser scanners

3D MODELLING OF “BANDUNG LAUTAN API”
MONUMENT BANDUNG (INDONESIA) USING
TERRESTRIAL LASER SCANNER
Irwan Gumilara, Hasanuddin Z. Abidina, Rezza Riawana, Nabila Sofia Eryan
Putria
a Geodesy
Research Group ITB
Jln. Ganesha 10 Bandung, Telp. +062-22-2534286,
Email: [email protected]
OUTLINE
1
INTRODUCTION
2
METHODOLOGY
3
4
ANALYSIS AND DISCUSSION
CONCLUSION
INTRODUCTION
The city of Bandung is a city with
many historical monuments or
heritage sites. One of the historical
buildings in this city is the
Monument of “Bandung Lautan
Api”. This monument is shaped like
a large fire torch. The monument
was built on 1981 and designed by
Drs. Sunaryo.
One way to preserve, conserve,
and archive is by creating a 3
dimensional (3D) model. One
method to create a 3D model is
by using the Terrestrial Laser
Scanner (TLS)
Survey Technology Development
(Courtesy by Leica Geosystem)
METHODOLOGY
Laser Scanning describes a method where a
surface is sampled or scanned using laser
technology. It analyzes a real-world or object
environment to collect data on its shape and
possibly its appearance (e.g. colour). The
collected data can then be used to construct
digital, two-dimensional drawings or threedimensional models useful for a wide variety
of applications.
The advantage of laser scanning is the fact
that it can record huge numbers of points
with high accuracy in a relatively short
period of time. It is like taking a
photograph with depth information.
Terrestrial Laser scanners are line-ofsight instruments, so to ensure complete
coverage of a structure multiple scan
positions are required (Quintero et al,
2008).
(Quintero dkk. 2008).
Block diagram of a pulsed laser rangefinder
Time
discrimination +
time interval
measurement
Stop
pulse
Start pulse
Amplifier
with AGC
Transmiter
Preamplifier
Detector
Range result
optics
𝑅=(𝑐 𝑥 𝑡)/2
𝑅: the distance between the TLS and the object;
𝑐: the speed of light on air (≈ 3∙108 m/s);
𝑡: the time travel of the laser when it is emitted
and received
(Reshetyuk, 2009).
Target
Principle of Terrestrial Laser Scanner (Reshetyuk, 2009)
Research Methodology Scheme
• TLS data acquisition
• Registration process
• Filtering
• Georeferencing process
output
• 3D modeling
Data Acquisition
Leica C-10 Performance
Spot size
4.5 mm @ 0-50 m
position
6 mm @ 50 m
Distance
4 mm @ 50 m
Angle (H/V)
(12”/12”)
Modeled surface 2 mm
precision
Target
acquisition
2 mm
The scheme of placements of device and
targets (a), documentation of TLS data
acquisition (b), and GPS data acquisition (c)
Gumilar et al. 2014
Registration and Filtering
The registration technique used in
this research is target based
registration. This technique uses a
minimum of 3 target points.
Before filtering
The error values of the registration
are obtained from the target scanning
process which is used as reference
points. In this research, the average
value of the registration error is
0.004 m. The largest registration
error value is 0.006 m.
During the TLS data acquisition, all
objects were scanned, both the
necessary and unnecessary ones.
After filtering
Georeference
This process requires two reference
points with known coordinates. One
reference point with the known
coordinates is the location of the
device (ST01), while the other one
is the location of the target, which is
used as backsight (BS). Based on the
two points as obtained by GPS data
processing, the georeferencing
process can be done using the
known azimuth technique.
Coordinates of BS point and azimuth of BS-ST01
(αBS-ST01)
Easting (m) Northing (m)
Heigh (m)
BS
787906.995 9232783.105
713,715
αBS-ST01=297°18'47.73"
3D Modelling
After all the point clouds have global
coordinates, the next step is 3D
modelling. This step starts with the
process of meshing. Meshing is
converting the point clouds data into
polygons with TIN (Triangulated
Irregular Network) format.
The process of meshing can be done
using Cyclone or Geomagic Studio 2013
software.
ANALYSIS AND DISCUSSION
Analysis of Registration Process
The registration error of the same
target at different stations can be of
different values for each station. The
difference of registration error is due
to the effects of levelling of the TLS
and targets. This is because the
positions of the niveau are different
for each station. The difference can
also be due to rotating the position
of the targets which can displace the
position of the niveau of the target
itself.
Analysis of Filterization Process
The difference in the results before and
after filterization process shows the
presence or absence of the noise in the
model space after filterization. The
presence of the noise in model space is
caused by accidental scanning the
unwanted objects. The objects which
are considered as noise include trees,
fences, statives, targets, humans, and
garbage around the object.
before (point coulds)
176,168,218
After (point coulds)
147,243,70
Filtering (%)
16.42
Analysis of the Mesh Process and Hole Filling
The surface as formed during the fill hole
process consists of 2 shapes, namely the
flat shape or curved shape. The flat shape
was formed by connecting the points
around the holes. The curved shape was
formed based on the points and the
surface shape around the area of the
holes. There were 96 holes in the model
because during the meshing process
Analysis of the Measurements
The measurement results are useful
for reconstruction and rehabilitation
in case of damage of the monuments.
The validation using distometer was
done to ensure the size of the model
fits the actual measurements
(in meter)
Validation
By comparing the
size as measured by
the TLS with the ones
measured
by
distometer
and
measuring tapes, the
average difference of
distance of 5-10 cm
was obatined. This is
due to the levelling in
every station and the
registration results
that were explained
in the analysis of
registration results.
Textures Analysis
The textures as obtained from 3D
modelling resemble the actual
condition, because during the
meshing process, the detailed
textures of the monument were
formed.
Model
Real condition
CONCLUSION
1. 3D model of heritage monuments can be done by processing the point clouds data as
obtained by the Terrestrial Laser Scanner measurements. In the resulting 3D model
of “Bandung Lautan Api” Monument, the height of the monument from its base is
20.325 m and the height of the monument from the surface of the ground is 22.501
m.
2. During the 3D modelling process, the average error value is 0.002 m. The error value
resulted from the registration process is due to the difference of the niveau positions
during the levelling of the laser scanner at two different stations.
Thank You