Full text: New perspectives to save cultural heritage

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

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