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THE NATIONAL TECHNICAL-SCIENTIFIC CONFERENCEModern technologies for the 3RD Millenium ORADEA, 2009

Application of scanning techniques in the creation of

three dimensional modelsSUBA tefan1,

UBA Norbert - Szabolcs2,

NISTOR Sorin3,

BUDA Aurelian - Stelian4,

ABSTRACTThis paper aims to present applications of the scanning process, using total stations

and spatial stations. Studies are made for the evidence of possible effectives of recording

characteristic points, which help us to obtain the three dimensional model, after makingthe proper calculations and modelling. There are two main directions for the applications:(1)the restoration of monuments and (2) the calculation of volumes.

Keywords : 3D modelling, spatial stations, scanning, restoration, volume calculation

INTRODUCTION

Nowadays theres an increased demand regarding three dimensional

models, partially because the lowered costs of the data collecting and

processing hardware and software, but also thanks to the ease of decision

making, both for the restoration of monuments and for volume calculations,

and also in the domain of infrastructure projecting. In this paper we will

present three different applications, for the use of scanning techniques in

creating three dimensional models.

1. Studied objectivesIn what follows, we will present three scanned and 3D modelled

objectives, and namely:

- Ullman palace, Oradea ceramic bas-relief, objective scanned for

preservation and restoration

- wooden military church, Oradea objective scanned for the

inventory of cultural folk patrimony, at the initiative of the "Accent"

Association for Culture, Education and Development from Oradea andthe Minister of Culture, Cults and National Patrimony

1 lecturer PhD. stud. eng., University of Oradea, Faculty of Arhitecture and Constructions,

e-mail: [email protected] univ. prep. PhD. stud. eng., University of Oradea, Faculty of Arhitecture and

Constructions, e-mail: [email protected] univ. prep. PhD. stud. eng., University of Oradea, Faculty of Arhitecture and

Constructions, e-mail: [email protected] lecturer PhD. eng., University of Oradea, Faculty of Arhitecture and Constructions, e-

mail: [email protected]

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SECTION: Architecture, Construction, Cadastral Survey, Sanitary Engineering AndEnvironmental Protection

- stone quarry, Urvi locality, Bihor county objective scanned

because of necessity, and because of the constraints by the Minister of

Economy and Commerce of a series of normatives regarding the

regular calculation and reporting of the stone quantity extracted at

every three months of time

2. Presentation of the used hardwareFor data acquisition we used two different, yet quite alike sets, both

having the possibility of 3D scanning. These two are the Trimble S6 Total

Station and the Trimble VX Spatial Station. In the following table we will

compare the characteristics of each of the sets (more precisely, the

characteristics of the models at our disposal) from the point of view of theinterest regarding the scanning process.

Tabelul 1. Comparision between the Trimble S6 and the Trimble VXTrimble S6 Trimble VX

selection of scanned

surface

polygonal, rectangle, specify

3 points, through the telescope

polygonal, irregular, n sides,defined on the touch-screen

angle accuracy 5 (1.5 mgon) 1 (0.3 mgon)

distance

accuracy

Standard (3 mm + 2 ppm) (3 mm + 2 ppm)

Tracking (10 mm + 2 ppm) (10 mm + 2 ppm)

scanning

speed

Standard 1 point / 1 - 5 sec. up to 15 points / 1 sec, average

5 points / 1 secTracking 1 point / 0.4 sec

built-in camera no yes, 3.2 megapixels

min. dist. between pts. 10 mm 10 mm

3. Presentation of the used softwareThe software used for processing the point clouds, respectively for

creating and viewing the three dimensional models were Trimble

RealWorks, respectively Cyclone from Leica Geosystems. Topographic and

positioning calculations were resolved using Trimble Total Control, Trimble

Business Center and TopoSys software. The software used for data

acquisition (installed on the field controllers of the total stations) was the

Trimble Survey Controller.

4. Case studies presentation of the scanning and processingtechnique4.1. Ullman palace, ceramic bas-relief Oradea

In this study case, we used the Trimble VX Spatial Station, with the

scanning area defined by a polygonal rectangle and with the horizontal and

vertical scanning intervals set to 1 centimetre. When using this total station,

we have the opportunity to define the area to be scanned by pointing the

edges of the polygon on the touch-screen, where we can see the image of the

object shown by the 3.2 megapixel camera. Beside the collectedpoints, the

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Trimble VX will take photos of the defined scan area, storing all these data

in a *.jxl extension file, which can be processed only using the software of

the same company, Trimble RealWorks.

After processing the field data we obtain the coordinates of each and

every scanned point, which make up the point cloud. The conversion

process used to create a usable 3D model from the point cloud is called

reconstruction or modelling. A point cloud is considered being an

unstructured grid of points, on which we can apply a coating, called a mesh.

A polygonal mesh is a collection of nodes (vertices), edges and faces which

form the shape of a polyhedral object in 3D computer graphics, with the

faces being compiled mainly from triangles or rectangles. This mesh,

applied to the processed field data, will result in a metrical threedimensional model, and respectively, in a negative of the scanned objective.

When creating the mesh, we used the TIN (Triangular Irregular Network)

method, with the triangles created from the point of view of the total station.

Fig.1. Point cloud bas-relief, Ullman palace, Oradea

Fig.2. Reconstructed object bas-relief, Ullman palace, Oradea

One advantage of this software is that it allows a wide range of

interrogations to be made, from the attributes of points to the distance in

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space between them, area and volume calculations, and so on. All this

because the software used is a workspace and not only a visualizer (as in the

case of many similar programs, which allow only viewing the 3D model).

Another interesting feature of this software is that it allows us to overlay the

created 3D model with the photos made on the field, thus creating a real 3D

view of the objective, an intelligent photo, on which we can make

calculations, and also preserve the real world aspect of the objective.

Fig.3. Reconstructed, textured object bas-relief, Ullman palace, Oradea

The built-in camera of this total station (Trimble VX) doesnt always

live up to our standards in terms of image quality. The lack of possibility to

control the point of focus of the camera, or settings regarding the contrast or

brightness when takingpictures, leaves us longing for more, especially inthe case of huge objectives, or objectives scanned from multiple stations,

when lighting conditions could change from one station to another. Because

of this, and also to achieve a better quality of the picture (and, obviously, of

our work), we replaced the photos taken with the Trimble VXs internal

camera with photos made with a digital SLR camera, using a Sony Alpha

A100. The advanced settings of the camera assures a uniform texture (as we

can see in Figure 3) and a highly superior quality of the picture, mainly for

those interested in the finest details of the scanned objects aspect.

4.2. Wooden military church Oradea, Universitii streetOn this occasion, we used once again the Trimble VX Spatial Station.

Because of the mixed configuration of this objective (large, strewn areas,

without considerable details (roof) and areas with zones of fine details

(pillars, carved areas)), we used different scanning intervals, spanning from

1 to 15 centimetres both horizontally and vertically, based upon the

scanned area. Also, the nature of this work and its complexity required

scanning to be made from several stations. The scan area was defined by a

multiple edge polygon. We should pay distinctive attention to the closure of

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the measurement network around the objective, as experience shows that an

orientation closure error may result in faulty positioning of points measured

from that station, and lead to the erroneous creation of the three dimensional

model (which will not reflect the real world situation).

Field data obtained from scanning was processed using Trimble

RealWorks software. The mesh creation method was the same as at the

earlier case TIN, with multiple triangle creation methods applied. Our

observations regarding this case were the following:

- because we were not able to do a scanning of the object

perpendicular on all of its elements (for example tower, roof), this led

to irregularities, where the software was practically forced (lacking

sufficient details) to guess the mesh to be created, regardless of thesettings made wed like mention that existing natural and artificial

obstacles prevented us from setting up stations further from the

objective in order to widen the scanned area, and thus to eliminate

some of the lack of details

- being given the huge number of details, respectively the lack of

speed the Trimble VX has compared to a dedicated field scanner, we

had different lightning (and even different meteorological) conditions

between the stations, which had a negative impact upon creating the

intelligent image of the object

Fig.4. Wooden church Point cloud and reconstruction

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4.3. Stone quarry Urvi locality, Bihor countyFor this study, we used the Trimble S6 Total Station. The objectives

in this case, listed below, were in concordance with the constraints of the

Minister of Economy and Commerce, and also defined by the necessities of

correct mining and stocktaking:

- fixing the correct height of the mining scarp

- width of the scarp

- possibility to extend the mining field

- evaluate the degree of risk

- possibility to arrange the access roads

- volume calculations

- possible elaboration of a plan for closing the quarryIf on the earlier occasions it was enough to determine locally the

position of the scanned points, in this case we had to make a correct and

rigorous positioning, in order to be able to repeat the measurements at any

time later, under the same conditions, to constantly track the specific details

of this job, a requirement which has to met by the processing software, too.

In order to obtain our coordinates in the national Stereographic 1970

projection system, we used GPS receivers (three single frequency receivers

Trimble R3 and one with double frequency Trimble R6) to determine

station points, outside the zone affected by the quarrys mining process.

Upon processing these observations, we used data from the permanent

stations of Oradea, Deva and Baia Mare. Point altitude values weredetermined using geometrical levelling closed on the starting point (using a

Leica Sprinter 200M digital level), with the starting point being in Urvi

locality, at the railroad station, with its altitude value determined in the

national reference system Black Sea 1975. Using these points, we

eventually determined another two points in the quarrys mining area, from

which we commenced the scanning process.

As we mentioned before, the scanning interval is chosen based upon

the jobs necessities, as well as the properties of the scanned area. In this

case, the scanning interval was set to 1 meter when scanning the quarry

walls, respectively 0.5 meters when scanning the scarps and areas with a

high degree of irregularities. Scanning areas were defined by rectangularplanes, and in high interest zones we further enhanced the precision by

adding manual observations (readings).

The data resulted from the scanning process was calculated in the

TopoSys software, whereas the three dimensional model was created using

Leica Cyclone software, with the mesh being created using the TIN method.

On this three dimensional model we can make operations defined by the

jobs objectives (fixing the correct height and width of the mining scarp),

we can make studies (possibility of extending the mining field/scarp), and

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we also have the possibility to make volume calculations (when overlaying

this 3D model with another model, created from a new set of

measurements), contributing to enhance the quarrys material and

economical efficiency.

Fig.5. Stone quarry, Urvi locality, Bihor county

Fig.6. Three dimensional model - stone quarry, Urvi locality, Bihorcounty

CONCLUSIONSThe scanning and the three dimensional modelling technique has a

large applicability but the development of the technological background,

data acquisition hardware and dedicated data processing hardware and

software, brings new possibilities of harnessing this technology. The

development of these technologies can bring an impressive drop of costs.

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Application domains for the three dimensional technology extends from the

heavy industry (machinery and tool planning) to the entertainment industry,

and far beyond. Understandably, both possibilities and demands for this

technology are continuously growing.

Three dimensional models, created as the result of the scanning

process, can be used for preservation and restoration of cultural objectives,

bas-reliefs, statues (mentioning some already existing projects, for example

the Michelangelo project), and with the use of the so-called 3D printing, we

can even create three dimensional, real world replications of these. We

would also like to mention that this scanning process will replace the

traditional plaster casting technique, which in many cases can be too

invasive for being performed on precious or delicate cultural heritageartefacts, and it was a hard job to do on entire facades.

Another applicability of this scanning would be the calculation of

volume for earthworks and mining, processes which were considerably

improved since the use of this technology, with the possibility of precise

estimations for further exploiting. The uses of intelligent photos or images

are also a great benefit for several industries, and also for art purposes.

Beside the large applicability of this technology, we can affirm that

the aspect of our works are greatly improved, and the investment made in

data acquisition hardware and processing software is justified by the

multitude of possibilities offered by this technology.

REFERENCES

*** (2009), Trimble Navigation Limited,www.trimble.com, 10.2009*** (2009),Leica Geosystems AG,www.leica.com, 10.2009*** (2009), Wikimedia Foundation,www.wikipedia.org , 10.2009

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http://www.trimble.com/http://www.trimble.com/http://www.leica.com/http://www.wikipedia.org/http://www.trimble.com/http://www.leica.com/http://www.wikipedia.org/

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