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New perspectives to save cultural heritage
Altan, M. Orhan

D. P. Andrews*, N. J. Beckett, M. Clowes, S. M. Tovey
English Heritage, Metric Survey Team, 37 Tanner Row, York, YOl 6WP, UK
Corresponding author
KEY WORDS: Cultural Heritage, Archaeology, Conservation, Mosaic Floors, Rectified Photography, Orthorectification, CAD,
Historic floors which consist of mosaic or decorative tiles are often of high cultural or academic value, but by their very nature are
vulnerable to decay and damage. On the other hand floors and footings are often the only surviving parts of a ruined building,
especially in an archaeological context. They present particular conservation challenges and therefore often require a high quality
metric record. The English Heritage Metric Survey Team has approximately 20 years experience in the photographic recording of
mosaic and tiled floors. This paper will briefly review traditional analogue methods for producing a photographic montage and then
go on to describe the development of digital methods. Both single image digital rectification and orthophotography
(orthorectification using stereo-photography) will be examined. Methods for producing the required photography and control will be
outlined. This will include strategies for obtaining suitable photographic coverage as well as attempts to equalise exposure. Control
of different forms and levels of precision have been employed and their relative merits will be discussed. The advantages and
disadvantages of using montaged rectified photographs or multi-image orthophotography will be examined. As well as an image of
adequate metric precision there is also a need for correct colour and consistent colour balance. Maintaining a true representation of
colour throughout the chain of the various processes including delivery to the end user is a major challenge. The issues involved will
be examined but a total solution is yet to be found.
Recording historic floors has always been a challenge mainly
because they are characterised by large areas of repetitive
detail but also exhibit minor variations due to wear, damage,
repair or errors in the original creation. For these reasons an
image-based approach is usually employed. Before the
advent of digital image processing, producing a photographic
product which covered an entire floor was a difficult and
time-consuming job. More usually a compromise product
such as individual photographs and a key was accepted. The
development of digital rectification software and digital
photogrammetry has meant that it is now much easier to
produce a scaled photographic montage of an historic floor
that can be printed out or used in a digital environment.
Increased use of digital imagery has also brought its own
problems. In the past colour balance was only affected by
exposure and processing conditions, now every piece of
equipment and type of media used has an input.
Mosaic and tiled floors are an important part of our cultural
heritage and it is commonly agreed that it is desirable if not
essential to have records of such artefacts in order to aid
academic study, improve access and as a last resort should a
disaster occur. Any academic paper on the subject of mosaics
or tiles will be illustrated with photographs and drawings but
a scaled photographic product should give a better
understanding of the subject. A digital image of a floor can
be used on a web site, for example, to aid peoples’
understanding and enjoyment of it. In some cases this will be
the only way to experience the floor. This could be because
physical access is a problem for the disabled. Some floors in
working buildings may be covered with furniture and so not
normally entirely visible (Dallas in Fawcett 1998). In other
cases, mosaic floors have been only briefly revealed as the
result of an archaeological dig and must be recorded before
re-burial if they are to be studied in any detail. Floors are
inherently vulnerable to damage and wear. As well as the
obvious fact that they are walked on, and increasingly so in
the modem age of mass tourism, floors have also suffered
from among other things burials, the insensitive installation
of services and the theft of tiles and tesserae. Fawcett asserts
that the mass tourism of the past 50 years has caused more
damage to historic floors than that inflicted over the last 700
years of general use and abuse (Fawcett 1998). Many historic
floors are in working buildings such as Cathedrals so it is not
normally an option to completely prohibit foot traffic. For
this reason it is important to record floors to enable the
monitoring of wear. It is also one of the guiding principles of
conservation that all interventions, such as restoration work
are recorded. Even if wear is not a major problem and no
conservation work is planned, it will always be sensible to
have some sort of ante-disaster record in case of a
cataclysmic event. This record would in the worst case
become a substitute for the real floor if it were totally
destroyed, or become a guide to its restoration if salvageable
damage occurred.
The challenge in photographing a floor is achieving a
suitable vantage point. An ordinary photograph can be taken