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T W E N T Y T H I R D E D I T I O N

T H E B U I L D I N G C O N S E R VAT I O N D I R E C T O R Y 2 0 1 6

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PROFESS IONAL SERV I CES

SPECIFICATION

Survey work should be properly planned

from the outset and the required outputs

clearly understood and defined. Specification

for archaeological survey should involve

the client body and/or the statutory body

requiring the survey, the archaeological

advisor and the survey specialist. The latter

should be competent to advise on the relative

suitability of a range of survey techniques and

methodologies based on the client’s needs

and the most appropriate approach to a given

structure.

Ideally the statutory body should be

able to advise on standards for the work, the

nature of the outputs, the conventions for the

presentation of the survey and recording data,

and procedures for suitable archiving.

ADVANTAGES AND LIMITATIONS

Technology plays an increasingly important

role in informing conservation work, providing

the tools with which data can be gathered to

support analysis and understanding.

Large amounts of visual information can

now be gathered in minutes. This can be of

particular significance where speed is a factor

(in advance of irreversible change through

planned alteration, controlled demolition

or, as in the case of recent events in Syria

and Iraq, wilful destruction). Digital survey

and recording can also be beneficial where

inaccessibility is a factor, for example where

the building is fire-damaged or otherwise

unsafe, where the building is physically

difficult to access, such as a cliff-top ruin, or

where the expense of scaffolding is prohibitive.

It can also be particularly advantageous where

scale is a factor, allowing imagery of large

areas of substantial structures to be captured

at high resolution very cost-effectively.

As outlined, high-resolution three-

dimensional survey imagery can be modelled

to great effect. For the archaeologist this

allows exciting new possibilities for the

analysis of historic buildings. In the case

of complex historic structures the nuances

and irregularities of a structure can often

be highly meaningful and digital imagery

can be manipulated in a number of ways to

enhance the understanding of such nuances.

Conversion from colour to a grey-scale image

can dramatically increase visual clarity; light

can be cast across the surface from any angle

that can tease out constructional subtleties,

tooling details, marks and so on. The digital

image itself can be distorted in any dimension

to bring out detail that is invisible to the naked

eye. Manipulation of the colour scale can

improve contrast and dramatically enhance

the level of visible detail.

THE END-PRODUCT

The process of initiating a building survey,

although dependent on many factors, should

be based on a workflow process that takes into

consideration a number of factors, and will

often contain a range of techniques that can

be used to achieve the final product.

With the increasing variety and

sophistication of techniques available to

the surveyor, the archaeological recording

of important historic buildings and sites

increasingly requires close co-operation

between the survey supplier and the

archaeologist to service the client’s

requirements and to most effectively (and

most cost-effectively) achieve the desired

results. Such survey techniques are the tools

by which complex, extensive or inaccessible

sites can be rapidly and inexpensively

surveyed. The quality of the end-product

is determined by a combination of the

quality of the input data and the ability to

manipulate that data in terms of presentation

and understanding of the subject. Advanced

survey techniques are not a substitute for

the understanding that comes from long

experience, rather they complement it.

As the demand for 3D data rapidly

increases, the surveyor must use existing and

emerging technologies to provide 3D data

cost-effectively. A colourised, comprehensive

point cloud is an essential component of the

dataset which records a site but it should only

rarely be the actual deliverable. Most clients

are not yet clear or comfortable in specifying

their 3D requirements – the surveyor and

archaeologist have a key contribution to make

in defining a product-based specification for

these data and this will need to be tailored

to the building, its complexity and details, as

well as the desired outputs.

CASE STUDY: LINDISFARNE CASTLE

Recent survey work for the National

Trust (NT) at Lindisfarne Castle, which

is located in an exposed position on the

rugged Northumberland coast, proved a

challenging subject that required many

of the techniques described above. The

survey methodology was developed by

archaeologists in liaison with the NT, the

project architects, with survey providers and

a specialist in digitally modelled imagery.

The survey and recording elements

that related to the proposed works were

developed in an integrated project design,

or ‘written scheme of investigation’,

developed to respond to a broad range of

perceived requirements for survey and

archaeological recording at the site in advance

of a major programme of repair works.

The survey and recording processes were

necessarily closely interlinked, combining

the recording and analysis that will inform

the proposed works and, once the works are

under way, the recording of any new areas

of fabric which are revealed. Thus survey

and recording was planned as an integrated

Figure 4 Lindisfarne Castle: a point cloud generated from terrestrial laser-scanned data

Figure 5 General modelled framework of the castle