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8/13/2019 Heritage3D-Visits1

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Developing professional guidance:

laser scanning in archaeology and architecture

Visits March 2005

April 20th 2005


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Project overview

The Heritage3D project directly addresses four sections of the 1998 English Heritage Exploring our PastImplementation plan. The two principal aims of the project are to:

develop and support best practice in laser scanning for archaeology and architecture

disseminate this best practice to users along with the education of likely beneficiaries

In order to achieve these aims the project works towards five objectives:

Objective 1 production of a guidance note that demonstrates the products that can be generated fromlaser scanning

Objective 2 to update the current Addendum to the Metric Survey Specification to take into account thecontinuing advances in the technology

Objective 3 to increase the knowledge base of English Heritage by forming partnerships with externalsurvey practitioners/equipment manufacturers within the UK

Objective 4 to promote synthesis between disciplines within English Heritage by publishing andmaintaining a project website

Objective 5 to provide workshops on the use of laser scanning to educate archaeologists, architectsand engineers from within English Heritage.


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1. TABLE OF CONTENTS

1. Table of Contents............................................................................................................................. 32. Introduction ...................................................................................................................................... 43. Summary.......................................................................................................................................... 5


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2. INTRODUCTION

In March 2005 Dr David Barber, on behalf of the Heritage3D project, made visits to three UK basedorganisations involved in archaeology and laser scanning. This document summarises these discussionsinto four major themes. Over two days visits were made to:

A commercial archaeology practice- Wessex Archaeology (WA), Salisbury (Tom Goskar)

Wessex Archaeology is one of the largest archaeological practices in the country. The Trust for WessexArchaeology was set up in 1979 as a small unit in Salisbury. It now employs over 150 archaeologists, butretains its charitable status and its remit to encourage interest in archaeology and extend knowledge about itto a wider public.

English Heritage - Centre for Archaeology, Portsmouth (Tom Cromwell and Paul Cripps)10

English Heritage's Centre for Archaeology at Fort Cumberland, near Portsmouth, was established in 1999 bybringing together the Central Archaeology Service, already based in Portsmouth, and the AncientMonuments Laboratory, relocated from London. CfA was set up with the aim of becoming a national centreof excellence in archaeological practice, integrating work in the field, stratigraphic analysis, finds studies and

work in the laboratory; it provides a resource for English archaeology, working in partnership with units,universities and amateur groups, and a source of help and advice on policy and casework for colleagueswithin English Heritage.

Academic teaching and research institution - Southampton University, Department of Archaeology(GraemeEarl)

The Department of Archaeology at Southampton was founded in 1966. Dr Graeme Earl (Research Fellow)20researches computer techniques for the analysis and presentation of archaeological data. He is particularlyconcerned with the development and implementation of multimedia resources for archaeology, including theuses of virtual reality and other techniques for the interpretation of archaeological sites and for providingaccess to online archives.


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3. SUMMARY

The visits have been combined into general headings, rather than summarised by discussion. (Thequestions are intended to outline the general discussions rather than the actual questions used in the visits).

Users and perceptions Who are/likely to be the main users of laser scanning datasets? What are their

needs? What are their perceptions and opinions?

1. Users, and the benefits they experience, tend to be specific to datasets. Different levels of detail are30generally required to provide appropriate products. Many recording needs in archaeology are quitemundane and may not require the use of laser scanning.

2. Users include the curators and inspectors responsible for managing and maintaining buildings, sitesand monuments. They can/do inform the decision making process by using survey and laserscanning products to undertake proximity/visibility analysis and condition surveys (includingmonitoring). This information is provided to structural engineers, architects, and archaeologists fromcommercial organisations, academic institutions, the media, education, English Heritage and thegovernment.

3. Examples subjects to which laser scanning has been applied include:

scanning of small artefacts such as flint arrowheads and skull/bone fragments40

building facades, where the scanning itself might be subcontracted to a data provider but withvector extraction and archaeological interpretation is undertaken by the client

topographic survey where a high level of topographic detail is required quickly and the product isto be used for cross sectioning and light shading (previous topographic assessment has usedDGPS and total station survey)

large sites, such as Stonehenge, where airborne scanning gas been used, although survey isgenerally reliant on LiDAR data collected for non archaeological applications.

4. The general response to scanning is very positive, but some people are entrenched in traditionaltechniques, although there are fewer of these people as time goes on. Commercial hesitation hasbeen encountered with use of laser scanning prohibited in some cases. There is generally an50excellent response amongst colleagues within organisations, although sometimes only superficially.Some colleagues are, however, starting to enquire about using scanning within projects, althoughbudget constraints are always a worry. Some people see scanning as a black box to be usedwithout too much consideration.

5. There is a general perception (especially amongst non-expert users) that scan data must be right asit is done on a computer. It is seen as reasonable to use scanning for virtual reality (VR) applications,especially in the context of educational engagement, but there is some resistance against virtualreconstructions (which are often subjective).

6. There is a need to provide access to laser scanning data at a corporate level (especially LiDAR)through internal GIS systems. However, this requires appropriate desktop tools and data60management policies (see sections below).

ToolsWhat specific software packages do you use? What devices do you employ to analyse and interpretdata generated from laser scanning?

1. Tools used or seen as vital in all discussions include 3D Studio Max, ArcGIS and AutoCAD. Demon(http://www.archaeoptics.co.uk/) was also used to inspect data and Pointools(http://www.pointools.com/) has been trailed. Generally the point cloud itself is not used, andalignment/registration of data is undertaken by the data provider. None of the visited organisationsoperate a laser scanner themselves. A meshed model was the typical dataset used by thearchaeologist user.


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2. For data analysis, lighting techniques were the most commonly used tool for assessing changes in70geometry. Often this interpretation is undertaken using 3D Studio to render scenes with lightsources that change location.

3. It was noted that there is a need to provide tools that allow annotation of data and three-dimensionalmanagement/analysis of data. Future tools will make use of collaborative environments (based on

the concept of the GRID internet level data distribution/processing) to share, process and interpretdata.

DeliverablesHow do you receive or deliver products derived from scan data? Do you have/use standarddeliverables?

1. Deliverables/processing were provided on a case by case basis without automatically replicatingprevious work, thus delivery and presentation methods are not strictly defined. There is a need to80define the need of the survey before work is carried out.

2. Although 2D line drawings are being generated from scan data, there was a general feeling that the3D nature of the data must be maintained in the deliverable. 3D isometric drawings are sometimesused. For meshed models Alias Wavefront files are the main deliverable, but often these have to be

delivered as decimated files. Online delivery has been considered using Active-X plug-ins such asOctopus (http://www.archaeoptics.co.uk) based on/inspired by QSplat(http://graphics.stanford.edu/software/qsplat/) at Stanford University.

3. Single images and movies are used, but these require pre-thought as to what the client actuallywants to look at. Movies, however, retain user interaction, for example by being able to select theframe with a particular lighting angle, while allowing use on a computer without specialist software.90There was seen as no reason why scans couldnt be used as scaled images, for example in re-pointing brickwork (although the meaning of reflectance values needs to be given).

4. There was some discussion on the use of scanning to replace the drawing of artefacts. However,this is a process in which the expert recorder takes a lot of pride, and although there is potential forreplacing it might be difficult to convince people. However, it was highlighted that drawing is

subjective and any output is an interpretation, even though it is often perceived as a faithfulrepresentation.

Pros and cons What do you see as the main advantages of using laser scanning? What are its strengthsand weaknesses?

1. If airborne LiDAR is used in archaeological applications the user normally has to resort to using100previously captured data. However, available commercial data (such as from the Environment

Agency) often has vegetation removed using semi-automated algorithms, which make them of lessuse for archaeology as the resulting surface may have processing artefacts that can be confusedwith archaeological features.

2. Typical to find that a primary user of laser scanning data requires additional computer power overexisting machines before being able to use point cloud/un-decimated meshes produced by laserscanning.

3. Photography was seen as allowing up-font interpretation through the choice of sun angle or aspectand as a technique that reduces the up-front fieldwork cost, as geometric data collection can becommissioned later on if necessary. Laser scanning is seen as allowing less up-front interpretation110with larger up-front costs but allowing objective recording (although interpretation might still besubjective).

4. Photography users are restricted to an east-west illumination, where as artificial lighting can beprovided from any direction using a rendered geometric model. There was some discussion as tohow many features have been missed on photography (airborne and terrestrial) due to

choice/unavailable lighting conditions. However, it is was considered unlikely laser scanning willprevent incorrect interpretation, or features being missed.


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5. Reported difficulties in using large amounts of geometric data often resulting from laser scanningwithin 3D Studio.

6. Some users reported variable data quality form project to project when dealing with contractors.120

7. Laser scanning isnt seen as a useful trench tool, but is of obvious use in environments like caves

and in providing a framework to which other data/interpretation can be attached.

Archive issuesSpecifically, how do you deal withthe archivingof laser scanning data?

1. No formal archive strategy especially for laser scanning was evident. Existing data managementprocedures seemed to be normal. Notably, ASCII data files were exported to provide an additionalformat. Optical backup made offsite, normally at close down of a project. Data archives in the orderof around 10 12 GB reported.

2. Some problems experienced with CDs which, over time have started to degrade. The same worryexists for DVDs but at present they are too new to notice any changes.

Other130

1. An increase in scanning was generally seen as likely. One visit suggested that scanning fortopographic surveys would see an increase, close range scanning is anticipated to be quite a smallpart of this work and scanning for building measurement/analysis will see little or no change.

2. The economic cost of any technique is a major issue in archaeology. Commercial archaeology inparticular is driven by cost, and the use of paper and pencils is often preferred to potentiallyexpensive technology.

3. Although virtual reconstructions were seen as feasible it was recognised that it is also aboutexperiencing the landscape and the emotional response that creates. By providing greater fidelity ofthe landscape/subjects involvement might be increased. However, there is a need for an audit trailin visualisation that might otherwise lead to subjective interpretations, although it is unclear how can140this be done.

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