International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B5. Istanbul 2004
via an image. The image would 'allow the automatic
identification of individual components within a defined 2D
area (x and y, using a click-and-drag box). Alternatively, the
image would allow the automatic identification of individual
components that were related in the z dimension (those
including a specific x,y coordinate identified with a single
mouse click). Individual components could be identified by the
conservator on one image (say, that of the X-ray or reverse) and
that component’s location could be viewed (suitably
transformed) on another image (say, that of the front).
The hierarchy and the image both allow access to the database,
which consists of a series of records. The “identity” record
holds administrative details of the object (title of the work of
art, the name of the painter, etc). The “photography” record
holds details of all photographs taken (location of area
photographed, stage of treatment documented, etc). In addition
to these global records, each individual component has a
number of records associated with it, which can be updated by
the conservator. The “structure” record holds data about the
original composition of a component (from the length, breadth
and thickness of an oak plank, to the colour and cut a of gem,
etc). The “condition” record holds data about the current
condition of a component (from ‘intact exemplar’ to
‘deliberately removed’, etc). The “examination” record holds
the results of scientific examination of a component (from the
dendrochronological details of an oak plank to the chemical
composition of a gem, etc). The “treatment” record holds data
about the sequence of a conservator’s interventions (from the
dates of treatments to the chemicals used, etc).
Er
Figure 11: Position of a hidden iron dowel with respect to the
painted image of Christ
All records can be searched by using the attributes with which
the hierarchy was constructed or by selecting keywords that
occur in the free text entered by conservators in their records.
The results of a search are presented as a list of the relevant
components, opening of the hierarchical structure in appropriate
places and highlighting the component’s outlined boundaries in
the digital image. This allows all the conservators (there are half
a dozen or so people with different expertise working on
different areas at different times) to know who did what where
and when.
In addition to this invaluable project management function, the
spatially referenced digital image also allows accurate
measurements to be made without direct physical contact with
the Retable itself. Accurate measurements are to be made for art
historical purposes to throw light upon the construction of this
400
thirteenth century product of international collaboration. Units
of measurement were not standardised, so was the Retable the
product of an English foot or a French foot, or possibly even a
Spanish or Italian unit of measurement? Also, irrational ratios
were commonly used in architectural constructions, so was the
design of the Retable based upon a proportion such as the
square root of two? Remote measurement with the 3D model
will allow us to answer such questions without risking further
damage to this historically important object.
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Figure 12: Position of the iron dowel (plus nineteenth century
screws) as seen in X-ray mosaic
5. CONCLUSIONS
The use of photogrammetric monitoring and surface measuring
tools within a purpose designed art conservation database has
significantly contributed to the treatment of the Westminster
Retable. The tools have also enhanced the conservator's
understanding and documentation of this unique object and will
assist in disseminating that understanding to a wider audience.
6. REFERENCES
Fraser, C.S. 2001 Automated Vision Metrology: À Mature
Technology for Industrial Inspection And Engineering Surveys.
The Australian Surveyor, 46(1): 5-11
Robson. S., Brewer. A., Cooper. M.A.R., Clarke. T.A., Chen. J.,
Setan. H.B., & Short. T. 1995. Seeing the wood from the trees -
an example of optimised digital photogrammetric deformation
detection. The International Archives of Photogrammetry and
Remote Sensing. Zurich 30(5W1): pp379-384
Papadaki, H., Robson, S., Chapman D. P. and Woodhouse N.
G., 2001. Obtaining accurate dense engineering data sets using
an integrated close range photogrammetry and machine vision
solution. Optical 3D Measurement Techniques V, Vienna,
October 2001. pp 319-326
Papadaki, H. 2002, Accuracy of Dense Surface Measurements
in an integrated photogrammetry and machine vision
framework. IAPRS, Corfu, Greece. Vol 34 Part 5 pp 68-73
Forstner W., Gulch E., 1987 *A Fast Operator for Detection and
Precise Location of Distinct Points, Corners, and Centres of
circular Features". ISPRS Proceedings "Fast Processing of
Photogrammetric Data", Interlaken, June, pp. 281-305
Gruen, A. Baltsavias M, 1988 “Geometrically constrained
multiphoto matching”. Photogrammetric Engineering and
Remote Sensing, Vol. 54 (5), pp. 633-641
7. ACKNOWLEDGEMENTS
This conservation project is funded by the Heritage Lottery
Fund and the J. Paul Getty Trust.
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