3D MODELLING OF “BANDUNG LAUTAN API” MONUMENT BANDUNG (INDONESIA) USING

TERRESTRIAL LASER SCANNER

Irwan Gumilara, Hasanuddin Z. Abidina, Rezza Riawana, Nabila Sofia EryanPutria

a Geodesy Research Group ITB Jln. Ganesha 10 Bandung, Telp. +062-22-2534286,

Email: igumilar@gd.itb.ac.id

OUTLINE

INTRODUCTION1

METHODOLOGY2

ANALYSIS AND DISCUSSION3

CONCLUSION4

The city of Bandung is a city withmany historical monuments orheritage sites. One of the historicalbuildings in this city is theMonument of “Bandung LautanApi”. This monument is shaped likea large fire torch. The monumentwas built on 1981 and designed byDrs. Sunaryo.

One way to preserve, conserve,and archive is by creating a 3dimensional (3D) model. Onemethod to create a 3D model isby using the Terrestrial LaserScanner (TLS)

INTRODUCTION

(Courtesy by Leica Geosystem)

Survey Technology Development

METHODOLOGYLaser Scanning describes a method where asurface is sampled or scanned using lasertechnology. It analyzes a real-world or objectenvironment to collect data on its shape andpossibly its appearance (e.g. colour). Thecollected data can then be used to constructdigital, two-dimensional drawings or three-dimensional models useful for a wide varietyof applications.

The advantage of laser scanning is the factthat it can record huge numbers of pointswith high accuracy in a relatively shortperiod of time. It is like taking aphotograph with depth information.

Terrestrial Laser scanners are line-of-sight instruments, so to ensure completecoverage of a structure multiple scanpositions are required (Quintero et al,2008).

(Quintero dkk. 2008).

Block diagram of a pulsed laser rangefinder

Transmiter

Pre-amplifier

DetectorAmplifier with AGC

Time discrimination +

time interval measurement

Range resultoptics Target

𝑅=(𝑐 𝑥 𝑡)/2 (Reshetyuk, 2009).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

Start pulse

Stoppulse

Principle of Terrestrial Laser Scanner (Reshetyuk, 2009)

• TLS data acquisition

• Registration process

• Filtering

• Georeferencing process

output • 3D modeling

Research Methodology Scheme

Data Acquisition

Gumilar et al. 2014

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 precision

2 mm

Targetacquisition

2 mm

The scheme of placements of device andtargets (a), documentation of TLS dataacquisition (b), and GPS data acquisition (c)

The registration technique used inthis research is target basedregistration. This technique uses aminimum of 3 target points.

The error values of the registrationare obtained from the target scanningprocess which is used as referencepoints. In this research, the averagevalue of the registration error is0.004 m. The largest registrationerror value is 0.006 m.

During the TLS data acquisition, allobjects were scanned, both thenecessary and unnecessary ones.

Registration and Filtering

Before filtering

After filtering

Georeference

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"

This process requires two referencepoints with known coordinates. Onereference point with the knowncoordinates is the location of thedevice (ST01), while the other oneis the location of the target, which isused as backsight (BS). Based on thetwo points as obtained by GPS dataprocessing, the georeferencingprocess can be done using theknown azimuth technique.

3D Modelling

After all the point clouds have globalcoordinates, the next step is 3Dmodelling. This step starts with theprocess of meshing. Meshing isconverting the point clouds data intopolygons with TIN (TriangulatedIrregular Network) format.

The process of meshing can be doneusing Cyclone or Geomagic Studio 2013software.

ANALYSIS AND DISCUSSION

The registration error of the sametarget at different stations can be ofdifferent values for each station. Thedifference of registration error is dueto the effects of levelling of the TLSand targets. This is because thepositions of the niveau are differentfor each station. The difference canalso be due to rotating the positionof the targets which can displace theposition of the niveau of the targetitself.

Analysis of Registration Process

The difference in the results before andafter filterization process shows thepresence or absence of the noise in themodel space after filterization. Thepresence of the noise in model space iscaused by accidental scanning theunwanted objects. The objects whichare considered as noise include trees,fences, statives, targets, humans, andgarbage around the object.

before (point coulds) After (point coulds) Filtering (%)

176,168,218 147,243,70 16.42

Analysis of Filterization Process

Analysis of the Mesh Process and Hole Filling

The surface as formed during the fill holeprocess consists of 2 shapes, namely theflat shape or curved shape. The flat shapewas formed by connecting the pointsaround the holes. The curved shape wasformed based on the points and thesurface shape around the area of theholes. There were 96 holes in the modelbecause during the meshing process

Analysis of the Measurements

Gambar 6. Ukuran beberapa objek pada Monumen ”Perjuangan Rakyat Jawa Barat”

The measurement results are usefulfor reconstruction and rehabilitationin case of damage of the monuments.The validation using distometer wasdone to ensure the size of the modelfits the actual measurements

(in meter)

Validation

By comparing thesize as measured bythe TLS with the onesmeasured bydistometer andmeasuring tapes, theaverage difference ofdistance of 5-10 cmwas obatined. This isdue to the levelling inevery station and theregistration resultsthat were explainedin the analysis ofregistration results.

The textures as obtained from 3Dmodelling resemble the actualcondition, because during themeshing process, the detailedtextures of the monument wereformed.

Model

Real condition

Textures Analysis

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