Final Paper 3D Techniques

8/3/2019 Final Paper 3D Techniques

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Dimitrios Tzanakis

Yannis Psaromiligkos

Daune West

3D Techniques andTools for Preservation

and Visualization ofCultural Heritage


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Contents

Introduction

Research Problem

Presentation of the state of the art

Case study

Conclusions


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Introduction

Cultural heritage is priceless

Cultural heritage preservation and

documentation is essential


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Problems

Cultural heritage objects are spreadaround the world

Cultural heritage sites and monuments arealways in jeopardy (pollution, rain, sun,wind, fire, earthquakes, war actions)


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3D digitization and visualisation

of cultural heritage benefits

Restoration study

Model study

Digital 3D models creation

Model data base development of similar

objects

Virtual museums


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Research Problem

What are the main techniques and tools inorder to:

model and visualize cultural heritage objectsdigitally with the use of InformationTechnology according to the context ofcultural heritage documentation andvisualisation


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Presentation of the state of the art

3D laser scanning techniques

Photogrammetry techniques

Visual description of 3D objects


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Main 3D laser scanning

techniques

Time of flight of a laser pulse

This methodology is also known as LightDetection And Ranging (LIDAR).

Laser Triangulation


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A laser pulse is emitted tothe object

The distance between the signalsending device and the surface ofthe object is calculated from therequired time between transmission

and reception of the laser pulse.

Time of flight of a laser pulseor Light Detection And Ranging (LIDAR)


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A CCD sensor using the high optical definition of a laser beam,that is projected on the under study object, and via triangulation

equations, calculates the position of each point that isilluminated by the laser beam in the 3D space.

Laser Triangulation


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laser scanning techniques

(+) More reliable and more usable by nonexperts in many projects

(-) Require many man hours

(-) Expensive

Suitable for large scale cultural heritage

surveying projects => high accuracyproducts with significant efficiency.


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Main photogrammetric

techniques

Stereophotogrammetry

Convergent or non-stereoscopicphotogrammetry

Structure from motion


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Stereophotogrammetry

Axes of camera should be parallel in twoconsequent shooting positions and vertical tothe surface of the under study object

Photogrammetric triangulation


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Convergent photogrammetry

The camera axes converge toward thegravity centre of the object

Marked Feature Points (a, b, c)


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Structure from motion

Automatic calculation of the orientationfrom marker-less photos.

Un-ordered photo sequences can be used

for input


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Photogrammetry techniques

(+) Ideal for cultural heritage objectswithout complex shapes

(+) Ideal when money, location andtime constraints exist

(+) Much more flexible in the case ofmulti dimensions projects than laserscanning techniques

(-) Experienced operators


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Point Cloud

Each pointcorresponds to afeature point andembeds 3Dcoordinates


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Triangular mesh is used in most 3Dimaging applications

Provides much more visual information

than the point cloud

Teapot wireframe rendered teapot



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Case study

Photogrammetric techniques selection

evaluation:

More appropriate for the case studyaccording to time, money and other

constraints

Essentially fulfil this case studysscope for visualisation and virtual

reality as well as its requirements


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Software tools

Arc3D Webservice

MeshLab

PixMaker Pro

Equipments A tripod

Two consumer photo cameras


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The Cultural Heritage object

Saint Tryfonas Orthodox Church,

Eleonas, Peloponnese


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ARC 3D Webservice

The 3D models were created by the ARC3D Webservice, developed by the VISICS

research group of the KatholiekeUniversiteit Leuven in Belgium

The uploading procedure required manyattempts and time to achieve usable

results Open source


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MeshLab

Developed by Visual Computing Lab of theInstitute of Information Science andTechnologies of the Italian National

Research Council CNR-ISTI in Italy 3D triangular mesh processing tool

Provides functions for cleaning, editing,

simplifying, remeshing, measuring,merging, visualising, converting, etc.

Open source


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MeshLab

(+) Can import meshes (models) in manyformats and export the results in almost allknown formats

(-) Not so stable, has no undo function andneeds great computer processing power

(-) Significant training time

(-) No complete manual (-) A lot of man hours to process the sub

scenes meshes and align and merge them

into the final model


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Case study

The procedure


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In order to create a 360o model, one mustdivide the 360o scene into individual sub

scenes

ARC 3D is not able to provide 3D data for

model creation that encircles an object


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The upload tool enables the user to beconnected to the Webservice and after

authentication to upload a selected sequence ofphotos to Arc3D server.

Users

can uploadunordered

and marker-less photos.


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ARC 3D Webservice

Automatic procedure in the server side

Parallel processes running on a cluster of

Linux personal computers


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The results:

camera parameters,

range-dense depthmaps (i.e. pointclouds), texture andquality maps forevery photo

Arc 3D Webservicecalculates the 3D data

and camera parame-

ters for each photo


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The 3D models were post processed byMeshLabs Arc3D import interface.

Main post processing functions: subsampling,

cleaning,

noise filtering, hole filling and merging.

MeshLab


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The four 3D partial models were importedand cleaned in MeshLab

They are all loaded into the same newMeshLab project and while they hadoriginally positioned in different reference

spaces

MeshLab


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they were rototranslated in

order to be placed into the same

single reference space and finallyto be aligned and merged.


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Snapshots of the VRML model


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ResolutionSize

(uncompressed)

Size(compressed

with gzip)

Full resolution 100% 137,594 Kb 31,735

High resolution 64% 87,431 Kb 20,628

Medium resolution 25% 34,463 kb 8,298

Low resolution 13% 17,977 kb 4,405

Three different model versions of reduced

resolutions (decimated and compressed) Fast download time for users with slowconnections rates


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3D model high resolution (64%)


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Case study - Vitrual tour section

PixMaker Pro

Virtual tour Use of Java

www.stvtour.comule.com


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Case study conclusions

Photogrammetry techniques: low cost

medium training requirements

medium post processing time

sufficient accuracy models with hightexture quality

no need for laboratory conditions

fast data acquisition and multi dimensionobjects compatibility


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Case study conclusions

Structure from motion technique suitable for:

virtual reality applications andvisualisation purposes (although not

highly accurate nor stable enough)

provision of 3D models from un-orderedand marker-less photos


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Final Conclusions In many methodologies their evolution is

proportional to IT evolution

In 3D digitization techniques the storage,

processing, archiving, management andvisualisation of the acquired digital data canonly be realized by IT utilization

Modern IT technologies (e.g. Web, VirtualReality) offer easy access to cultural heritage

=> The contribution of IT in cultural heritagedocumentation is crucial:


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Final Conclusions

Nowadays there is no all-in-one culturalheritage objects documentation solution

The combination of different techniques inorder to achieve the matching of theiradvantages, a hybrid technique, may leadto a complete solution


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Final Conclusions

The most crucial limitation of photo-grammetric techniques is the software

If the development of IT and softwarecontinues its current pace, it will be

possible in the near future forphotogrammetry to overcome its basic

limitations providing the panacea incultural heritage documentation


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The future of cultural heritagepreservation and

documentation belongs to

Photogrammetry !


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Questions

Documents

Final Paper 3D Techniques