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International Archives of the Photog
scanning would have required investment in hardware
and software, which may have required the adoption of
proprietary formats and products. This was beyond the
scope of the project. Therefore, the addendum aimed to
facilitate the capture and delivery of data that would be
easily transferable between different software systems in
the future. Collected data includes the scan data itself, in
un-registered and registered form, images showing the
data collected, photographic images of the subject and
control information providing the ID, X, Y and Z
coordinates of each control point.
In addition to the collected data the addendum also
outlined the health and safety issues relating to the use of
lasers. For this purpose the addendum refers users
directly to the current European standard (IEC, 2001).
However, to facilitate an understanding of this
complicated document the user guide provides a brief
summary of the pertinent issues.
In order to provide a case study demonstrating the use of
the addendum on an actual site, a survey was undertaken
at Clifford’s Tower, York. How this survey fulfils the
metric survey specification and its addendum will be
described along with the benefits and issues experienced
during the survey. Prior to describing this survey,
however, the role of the specification in the project
flowline needs to be defined.
2. THE PROJECT FLOWLINE
Survey required - prepare
project brief
Tender period
Contractors prepare and
submit method statement
(including costs)
Survey commissioned
Survey undertaken
Y
|
|
|
I
| Survey delivery |
|
|
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y
| Quality assurance
Archive Use FE
Figure 1. The project flowline (dashed lines indicate
reference 10 the specification).
Figure | describes a typical project flowline. After
identifying the need for a survey to be undertaken, a
project brief is established by the client (in this case
English Heritage). The project brief includes information
that helps the contractor understand the site-specific
needs and requirements of the survey. It is written with
967
rammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B7. Istanbul 2004
direct reference to the survey specification which
prompts the client for the relevant information.
Once the project brief is prepared it is put out to tender
and survey contractors provide a method statement
detailing how they intend to undertake the survey. This
Will include the standard topics required for any survey
and outlined in the current metric survey specification.
This includes items such as a risk assessment and
delivery timetable/milestones. The specification will be
referred to in order to help the contractor understand how
the survey should be performed. The survey will then be
commissioned and undertaken. During this work the
contractor will generally be guided by the method
statement but will also refer to the specification for
guidance where necessary. Upon completion the client
will use the project brief and standard specification to
undertake a quality assurance process before accepting
the survey and passing it into the archive and/or on for
use.
3. SURVEY OF CLIFFORD'S TOWER, YORK
Figure 2. Clifford's Tower, York.
Clifford's Tower (Figure 2) is the surviving keep of
York's main medieval castle (Butler, 1997). It stands on
a 14 metre high defensive motte (mound of earth) at the
confluence of the River's Ouse and Foss. Although the
site dates from 1069, the present day stone tower was
built in 1245 under the orders of Henry III using a *four
leaf” design. The tower itself is 15 metres tall with a
diameter of 20 metres. Despite a period of neglect by the
Tudors, including an enterprising, but un-official, scheme
by the tower's gaoler to sell the structure stone by stone
in 1596, the tower remained in use until 1684 when it
was destroyed by fire. The extreme heat of this fire
turned some of the magnesium limestone masonry pink.
Since this time the Tower has remained a key piece of
York's cultural heritage and become an important tourist
attraction.
As a key tourist attraction for the city there is a need to
balance the conservation of the tower with providing the
facilities and services required by visitors. The risk of
further damage also requires an archive of survey data.
For example, although the motte is out of bounds to the
public its un-fenced grassy slopes are attractive to visitors
and gradual damage to the motte is inevitable. The tower
has also developed a noticeable lean due to gradual
subsidence, first noted in 1315.
photogrammetric data is available for the tower itself, no
Finally, although
