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.
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