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