T he attention of the scientific community Abstract The 3D - - PDF document

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Abstract—The 3D scanning laser systems available at ENEA, different for technical characteristics, allow to fullfil a wide range of diagnostic and monitoring requirements in the artistic and cultural heritage field. Since each scanning device is provided with proper file formats and software package for the data management and the reconstruction of the 3D

• bjects

acquired, the main problem in constructing complex graphical scenes is to integrate the 3D models preserving all the information detected. Accordingly, the development of Virtual Reality applications requires the analysis of the model file formats and the format conversion tools in order to define a methodology allowing to integrate the different systems and to build 3D scenes navigable by means of VR environments. As example, this paper refers to the development of a virtual museum exhibiting the different 3D models, acquired during various scanning campaigns, navigable by means of VR environments, available through the ENEA Grid. Index Terms— ENEA, CRESCO Project, GRID Computing, Virtual Reality, Cultural Heritage, Laser Scanner Technology, 3D Models. I. INTRODUCTION

he attention of the scientific community towards 3D digitizing techniques applied to cultural heritage is related to the specific needs of conservation: in terms of time and reliability, digital archives of high quality three- dimensional models would constitute a great improvement in respect of the past traditional methods of documentation. Digital archives are durable and unalterable, and thus can be used as reference for degradation monitoring and restoration activities. The scanning laser systems available at ENEA, acquiring 3D

• bjects and detecting information like position,

color and reflectance of each point, allow to meet a wide range of diagnostic and monitoring requirements in the artistic and cultural heritage

• field. Each laser scanning system is provided

with a specific software for the data management and analysis, capable to produce 3D models of the scanned objects in specific

• utput file formats. A test case was adopted, in
• rder to define a methodology allowing to

include such 3D models in the same graphical

• scene. The objective was to develop a “Virtual

Museum” in which to set up exhibitions, inserting/removing 3D models produced by

Laser Scanner Technologies and 3D Models Integration: Analysis and Methodological Approach

• D. Abate1, M.C. Baracca2, R. Ciavarella3, G. Furini4, S. Migliori5, S. Pierattini6

1ENEA, Bologna, Italy, dante.abate@enea.it 2ENEA, Roma, Italy, cristina.baracca@enea.it 3ENEA, Portici(NA), Italy, roberto.ciavarella@enea.it 4ENEA, Bologna, Italy, graziano.furini@enea.it 5ENEA, Roma, Italy, migliori@enea.it 6ENEA, Bologna, Italy, samuele.pierattini@enea.it

T

FINAL WORKSHOP OF GRID PROJECTS “PON RICERCA 2000-2006, AVVISO 1575” 1

different laser scanner system and to navigate the 3D graphical scene by means of the VegaPrime [1] environment

• r

the OpenSceneGraph [2] toolkit available by means of the ENEA-Grid [3]. The integration

• f the different laser scanning systems consists

in the definition of the conversion procedures

• f the 3D models, from the specific output file

formats to the OpenFlight format (.flt) [4], supported by both the chosen virtual reality environments.

• A. Laser Scanner Systems in ENEA

Laser scanning technology allows the digital acquisition of three-dimensional objects as point clouds. The digital geometric description

• f the object is discrete, the resolution selected

for the acquisition defines the density of the point cloud and so the details of the

• representation. Every point is described by a

spatial position in x y z coordinates respect to the origin represented by the position of the

• scanner. Due to different characteristics of the

laser scanner systems in ENEA, it is possible to choose, case by case, the more suitable to be applied and to produce 3D models of objects with size ranging from tens of centimeters to tens of meters. ! ITR (Imaging Topological Radar) developed by ArtVisLab-ENEA [5] Output file format: PLY (Polygon File Format) with VCG extension library; SW package: ISIS ply viewer; ! HDS3000 by Leica-Geosystem [6] Output file format: DXF, DWG, MDL and PTS; SW package: Cyclone and Cloudworks module for Autocad; ! VIVID 900 by MINOLTA [7] Output file format: STL, DXF, OBJ,ASCII and VRML; SW package: Advantage Polygon Editing Software; ! Desktop 3D Scanner by NextEngine [8] Output file format: STL, OBJ, VRML and 3DS; SW package: ScanStudio CORETM. Since each scanning device is provided with proper output file formats and software packages for the data management and the reconstruction of the 3D objects acquired, the main goal in realizing complex graphical scenes is to integrate the 3D models in a VR application, through format conversion preserving all the detected information.

• B. 3D Models

The availability of 3D digital models not only does support the promotion and diffusion of the heritage by means of multimedia applications, but also permits to improve many processes like cataloguing, study, preservation, restoration planning and simulation, fragile artefacts monitoring, virtual reconstruction, replica production. 3D laser scanner devices allow to analyze real-world

• bjects
• r

environments, to collect data (point clouds) on its shape and possibly its appearance (i.e. color/reflectance). The collected data can then be used to construct digital, three dimensional models useful for a wide variety

• f

applications, including the exposition in a “virtual museum”. Here below, some 3D models produced by means of:

! VIVID 900

Old soldier and young soldier (Museum Certosa, Bologna)

FINAL WORKSHOP OF GRID PROJECTS “PON RICERCA 2000-2006, AVVISO 1575” 1

! ITR ! Desktop 3D Scanner ! HDS3000

• C. Conversion to OpenFlight format

The Open Flight format (.flt) is supported by both VegaPrime and OpenSceneGraph; from the analysis of the 3D models proprietary file formats and the format conversion tools, it was possible to define the 3D models conversion methods to OpenFlight format without loss of

• information. After analyzing and testing input

and output formats of the most common software for 3D model conversion, the following conversion schemes were defined: for PLY format:

• r

Polichrome pot 1 Emperor Costantino marble head (Museum, Frascati) Polichrome pot 2 Small artefact Basilica - Juvanum archaeological site

FINAL WORKSHOP OF GRID PROJECTS “PON RICERCA 2000-2006, AVVISO 1575” 1

and for STL or OBJ

• D. Positioning and scaling models in a 3D

scene Since every scanned object is represented in a 3D space, accordingly to the space configuration of the used scanner system, it is useful to refer all the models to the same space: by means of Accutrans 3D [9] it is possible to redefine the origin for each model and so refer it to the same space. Moreover, due to the different characteristics of the laser scanner systems, two further aspects must be taken in to account: ! Different scaling factor are applied to models originated by different systems; ! The number of points defining the mesh of a model usually is much higher than the one required for a VR application. LynX Prime, the editing tool of VegaPrime, allows to define the “scale” parameters to be applied along each axis to an .flt model. In this way it is possible to re-establish right proportions to the models. The number of points in a mesh can be decreased through the application

• f

decimation algorithms. For example, MESHLAB [10] allows to choose among some filter and statistical decimation algorithms.

• E. Virtual Museum

In the framework of the ENEA CRESCO project [11], it was decided to develop an application, running on the ENEA Grid, simulating a museum exhibition; that is, starting from the 3D geometrical modeling of a museum architecture equipped with textures, materials, lights, etc., to insert in the graphical scene some of the 3D models produced by means of different laser scanner systems. Once converted in the OpenFlight format, each model was correctly scaled and placed in the navigable museum environment, as shown in the pictures below; the Juvanum archaeological site model can be accessed navigating through a picture of the Juvanum archaeological park [12] placed on an internal wall. Museum exterior Museum interior

FINAL WORKSHOP OF GRID PROJECTS “PON RICERCA 2000-2006, AVVISO 1575” 1

• II. CONCLUSION

Adopted as a test case, the “virtual museum” results in a flexible and dynamic application, allowing to change/insert 3Dmodels produced by ENEA in different activities involving the use of laser scanner systems. It is a powerful tool for documenting project and collaboration results in the field of Cultural Heritage. Moreover it could be the basis for the development of a 3D multimedia application. REFERENCES

[1] Presagis Inc., “Vega Prime ,” http://www.presagis.com/products/visualization/detai ls/vegaprime/ [2] Bob Kuehne, Paul Martz, “OpenSceneGraph Reference Manual v2.2,” Bob Kuehne, Paul Martz, 2007. [3] S. Migliori, G. Bracco, P. D’Angelo, “L'architettura di ENEA-GRID,” Conferenza GARR 2005. [4] Presagis Inc., “OpenFlight format,” http://www.presagis.com/products/standards/details/o penflight/ [5] ENEA FIM Dpt, “Laboratorio di Visione Artificiale,” http://fim.enea.it/laboratori-e-impianti/laboratorio-di- visione-artificiale [6] Leica-Geosystem A G, “Leica HDS3000 3DLaser Scanner,”http://www.leicageosystems.com/hds/en/lgs _5574.htm. [7] Konica Minolta, “3D Measurement Instruments,” http://www.konicaminolta.com/sensingusa/products/ 3d [8] NextEngine Inc., “Desktop 3D Scanner,” http://www.nextengine.com [9] MicroMouse Productions, “AccuTrans 3D,” http://www.micromouse.ca [10] CNR ISTI Dpt., “MeshLab: an Open-Source Mesh Processing Tool,” http://meshlab.sourceforge.net/ [11] ENEA FIM Dpt., “CRESCO: Centro computazionale di RicErca sui Sistemi COmplessi,” http://www.cresco.enea.it [12] P.Staffilani, “La basilica, Le tabernae, Gli spazi funerari, Il ceto degli equites, in Juvanum. L’area archeologica,” Sinapsi Edizioni, Sulmona 2006, 73- 80, 109-111, 125-128.