Methodological contest between high-end hardware and low-cost equipment for archaeological documentation

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Undine Lieberwirth, Bernhard Fritsch, Markus Neteler, Markus Metz

Methodological contest

between high-end hardware and low-cost

equipment for archaeological documentation

keywords

structure from motion, image-based modeling approach, 3D geo-spatial field

technology, archaeological data acquisition, 3D laser scan, FOSS, GRASS GIS, high resolution digital documentation technique

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 Introduction -> Research question, State-of-the-art of digital documentation methods

 Aim -> Comparison of two methods

 Case study -> Ostia Antica

 Results -> And the winner is …!

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Undine Lieberwirth, Bernhard Fritsch, Markus Neteler, Markus Metz  Introduction  Aim  Case study  Results  Outlook

Research question

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 Introduction  Aim  Case study  Results  Outlook

State-of-the-art

of digital documentation methods in Prehistoric Archaeology

First application of terrestrial laserscanners in Prehistoric Archaeology by VIAS Wien

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State-of-the-art

of digital documentation methods in Prehistoric Archaeology

First application of terrestrial laserscanners in Prehistoric Archaeology by VIAS Wien

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 Introduction

 Aim

 Case study

 Results

 Outlook

Advantages & Disadvantages

- High quality and precise documentation - immediate control

- Hardware: quick and easy to use

- Software: can be operated intuitively after an introduction

- Fast and easy referencing and geo-referencing possible

- Fast data processing = data preparation

- Time consuming because of

mostly more than one scanworld is needed

- Every scanworld needs a new registration by scanning all targets = time consuming - Hardware: havy equipment - Difficult custum regulations in

certain countries

- Very expensive equipment - Software: Very expensive

proprietary for documentation and first data preparation

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State-of-the-art

of digital documentation methods in archaeology

Computer Vision / Structure-from-motion

- originally developed for Tourism / Social networking purposes

- Online-Services like Photosynth or Photofly for all all kinds of use: private, construction, forensics, design…

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Computer Vision / Structure-from-motion

- Adaption for archaeology as a low-cost alternative to laser scanning - different packages available:

- Proprietrary: Photoplan, Arctron aspect3D

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Advantages & Disadvantages

Advantages:

- little gear

- low-cost

- time-saving (on-field)

- more weather resistent

- flexible

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Disadvantages

- spatial cover

- post-processing (Workflow)

- no immediate control

- required compute power (but no cloud-computing necessary)!

- georeferencing

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Undine Lieberwirth, Bernhard Fritsch, Markus Neteler, Markus Metz  Introduction  Aim  Case study  Results  Outlook Comparison of two methods

Laserscanning

Structure-from-Motion

Hardware

Price High Low

Transport Heavy and difficult Just one photo camera ist needed Additional Equipment + Tripod, + Notebook, + certain

targets

No

Power supply Needed Needed

Acquisition time 6x as long as SfM

Workflow steps

distance, spatial cover The longer the distance, the lower the resolution . field of application Architectur, Prehistoric

Excavation.

Weather sensibility Not applicable by rain and temperature higher 40°C and

lower – 40°C. Handling management Difficult to handle

Software

Price high

Usability _{can be operated}

intuitively after an introduction Maintenance

Processing time Post-processing

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Office

Freyenstein

Ostia Antica

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Ostia Antica

1. 489.381, 702.880, 2.747

2. 490.217, 701.778, 2.813

3. 488.992, 702.380, 2.844

4. 490.498, 702.327, 2.781

1. 489.376, 702.918, 2.725

2. 490.206, 701.811, 2.813

3. 488.969, 702.372, 2.857

4. 490.475, 702.319, 2.767

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164 743 vertices

Laserscan

(resolution 1 mm, 1 Scanworld)

Structure-from-motion

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Ostia Antica

• Taking pictures: easy

• Taking usable pictures, some things to think of:

• Good camera objective helps

• large memory cards necessary

• Don´t forget targets for measurements and

color balance

• more cameras would even speed up

• assure the overlap!

• Laptop on site for instant check of photos and

running of small models

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Ostia Antica

Open-source: bundle of software needed:

• Image viewer/Graphics software

-> sort / rename images

• Linux: BundlerTools

-> create pointcloud

• Meshlab, CloudCompare

-> clean pointcloud, pick points

NEW: GRASS GIS:

.ply-Import/Export module + georeferncing (rectify)

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3D Georeferencing application flow:

1)

Import of the point cloud in different file formats: e.g. PLY, LAS

PLY Vertex-attributes included

v.ply.in

2)

Georeferencing of vectors in GRASS GIS

v.transform

3)

Export of the point clould in different file formats: e.g. PLY, VTK

v.ply.out

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3D Georeferencing

Affine and higher polynomial transformation based

on control points

The accuracy of the transformation is depended on

the accuracy of the control points

Affine transformation:

For each dimension separately: move, scale, rotate

Helmert-Transformation (coming soon!):

For each dimension separately: move, rotate

For all dimensions equally: scale

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 Introduction

 Aim

 Case study

 Results

 Outlook

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Future perspectives

Computer Vision / SfM (Open-source)

• Toolchain from digital images

to georeferenced 3D-model

available

Things to improve:

• Usability of software packages

- automatic target detection

• Database connection

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Co-operation between the

Excellence Cluster 264 - TOPOI Berlin/Germany

and

Fondazione Edmund Mach – Research and Innovation Centre Trento/Italiy