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type of survey addressed in the current metric survey
specification. Discussion and examples of TLS are therefore
limited to this class of system.
1.2 Project design
The project described in this paper has been funded through
the English Heritage Archaeology Commission’s budget. It
aims to produce an addendum to the existing metric survey
specification, thus allowing laser scanning to be considered
alongside existing techniques within the survey of the 400
monuments directly under the care of English Heritage and
many of England’s 450,000 listed buildings. It is, however,
important to understand that the inclusion of TLS in the
specification does not instantly deem it suitable for the
replacement of other survey techniques. It is normal that
before any survey work is undertaken a project brief is
defined. This should describe the variable elements of a
particular survey and hence it is the responsibility of this
document to define the appropriate technique/s. The
specification document produced from this project is simply
intended to define the level to which TLS, if appropriate for
use, should be applied. The document is also intended as a
guide for users. It is not intended to stifle the development of
TLS by imposing unrealistic or unnecessary constraints on
the application of laser scanning systems. In fact the project
explicitly aims to steer the development of laser scanning so
that it meets the needs of cultural heritage users,
archaeologists, architects and building historians.
An iterative process of specification, survey, consultation
and revision was used to define the specification. Based on
previous experience an outline project brief was agreed to
allow an initial data collection phase to take place. After
analysis of this data, a steering committee comprising nine
individuals (including the authors), was consulted. The
members of this committee were selected to represent both
the client and contractor. Contractors were selected from the
survey community, including those already offering
commercial photogrammetric or TLS services. End users
were represented by members of English Heritage, including
some from their Centre for Archaeology. After this review a
second survey was performed before the initial document
was again revised. This draft specification (English
Heritage, 2003) was then released for comment to the wider
UK survey community before a final survey to confirm the
suitability of the document (at the time of writing these two
stages are yet to be completed). This extensive process of
consultation will ensure the practicality, impartiality,
relevance and ultimate value of the final document.
2. OVERVIEW
From the outset it was clear that the specification could be
divided into three interrelated segments. These three
segments represent the clear logical progression of laser
scanning (or indeed any other survey technique): data
capture, data use and data storage (or archiving). Although
each segment depends on another, for example the methods
employed for data collection will implicitly depend upon the
intended use of data, using these three broad categories
allowed a structured approach to the project.
2.1 Data capture
The capture of data clearly depends on the scanning system
in use as this will dictate the workflow and techniques
applied. This includes issues such as methods for
registration, available/required field of views, the density of
data capture and the requirements for any additional
information.
2.2 Data use
Although scanning has been used for architectural survey for
over three years, standard products have yet to be defined.
The use of TLS data was therefore not specifically addressed
by the document with the main emphasis placed on the
collection and storage of point cloud data. However, in order
to make the specification sensitive to the needs of possible
end products the following were defined as potential outputs
although no specification of how they should be presented, or
to what level they should attain, was provided.
■ CAD models (by primitive modelling)
■ Meshed models
■ Profiles and cross sections
■ Animations
Work is still required to educate clients who commission
TLS that the production of traditional products (such as line
drawings) from scan data may not be the most appropriate
way of applying laser scanning.
2.3 Data storage
All survey data generated for English Heritage is ultimately
deposited in the National Monuments Record, Swindon, UK.
The storage of data is therefore a vital part of the
specification process. Access to the data must be possible
despite the possibility of a number of years passing between
data collection and processing. The biggest obstacle to this
is the current lack of a standard data format. A standard
format for TLS would allow for the efficient transfer of data,
improving software development and ensuring the continued
use of TLS as a technique to supply archive data. Any
standard data format also requires appropriate metadata to
allow for long term data storage and management.
3. FIELDWORK
Two separate surveys were performed at Tynemouth Priory,
Newcastle upon Tyne in February and May 2003. A further
survey is planned for Clifford’s Tower, York although at the
time of writing the details have yet to be confirmed.
Tynemouth Priory has been used on several previous
research projects looking at the application of metric survey
techniques (Mills et ah, 2000, Barber et al., 2002), in
addition to being the subject of several phases of survey by
English Heritage. As it provides a clear, open and local site
it was an ideal location for the first two surveys of the
project. Both surveys concentrated on the remains of the
priory church (Figure 1), a ruin approximately 92 m x 21 m
in size with the tallest structure reaching 22 m in height.
During the first visit a substantial survey was performed
