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ul 2004 
PERIODIC PHOTOGRAMMETRIC MONITORING AND SURFACE 
RECONSTRUCTION OF A HISTORICAL WOOD PANEL PAINTING FOR 
RESTORATION PURPOSES 
Stuart Robson", Spike Bucklow”, Neil Woodhouse“ & Helen Papadaki* 
* Department of Geomatic Engineering, University College London, Gower Street, London WCIE 6BT - 
srobson(@ge.ucl.ac.uk, hpapadak@ge.ucl.ac.uk 
" Hamilton Kerr Institute, University of Cambridge, Whittlesford, Cambs UK - sb10029@cam.ac.uk 
¢ Leica Geosystems GIS & Mapping, LLC 10840 Thornmint Road, Suite 100, San Diego, CA 92127, USA, - 
Neil. Woodhouse@gis.leica-geosystems.com 
Commission V, WG 4 
KEY WORDS: Monitoring, Archiving, Recording, Cultural Heritage, Databases 
ABSTRACT 
The Westminster Retable is a work of art occupying a central position in late thirteenth century painting in Europe. It is 3.4m long, 
Im high and about 0.1m thick and consists of an oak support which carries numerous decorative and structural features and materials 
including: wood carvings, paintings, glass, dowels, metal, stone and vellum. During the restoration process it is necessary to conduct 
environmental response monitoring and mechanical deformation checking to ensure the integrity of the Retable. A multi-image 
digital photogrammetric system has been chosen for this purpose since it offers a periodic method of non-contact recording. However 
the image record and its associated spatial data can be used for other purposes including providing the basis of a visual database used 
to manage the conservation process and to automatically generate a 3D surface model which allows the art conservator to make 
measurements and comparisons between different parts of the structure. 
This paper describes the use of a photogrammetric system for high precision monitoring during the conservation process using multi- 
photo network adjustments, camera calibration and stochastic deformation analysis techniques. The technique has been able to 
monitor discrete points on the surface of the Retable to precisions of 20 micrometers. Techniques are then described which have 
allowed the automatic generation of an accurate surface model from the multi-photo image record. This latter work draws upon an 
integration of point interest algorithms, multi-photo image matching, epipolar geometry, extracted lines and edges to automatically 
generate a dense point cloud and triangulated surface model. These methods are integrated within an error propagation model to 
ensure the precision and reliability of the extracted data. The model is currently being integrated into the art conservation database 
system with the aim of allowing conservators to make dimensional and shape comparisons between some 3000 different structural 
elements on the Retable. 
1. INTRODUCTION 
The Westminster Retable is the oldest surviving easel painting 
in Britain. It originally furnished the High Altar of the Abbey 
and was executed in Westminster during the second half of the 
thirteenth century. It was the product of pan-European 
collaboration — Henry Ill's accounts show payments to British 
painters as well as to painters from France and Spain, some of 
the techniques employed in the painting are Italian, and 
materials for it were imported from as far as Afghanistan. 
The core of the work was formed by six oak planks, which were 
joined by thirty-one iron dowels. Some of the front surface was 
carved to a depth of a few centimetres and the rest of the front 
was embellished with over one hundred smaller carved pieces 
of wood, attached with nails and wooden dowels. Joints in the 
wooden superstructure were sealed with parchment, and the 
entire surface was decorated. The reverse and all the edges were 
painted to look like porphyry, even though the Retable was 
embedded in a stone screen so the reverse and edges were never 
seen. The front was covered with gold leaf, painted scenes, 
stained glass, gems, enamels and cameos. The surviving painted 
scenes include three identifiable miracles from the life of Christ, 
together with figures of St Peter, St John the Evangelist, Mary 
and Christ. 
The Retable is in a very fragmentary condition and more than 
half the gold leaf, painted scenes, stained glass, gems, enamels 
and cameos are broken or completely missing. Some of the 
losses are due to the efforts of souvenir-hunters but other 
damages and losses are due to the inherent properties of 
  
  
Figure |: Detail from the front surface of the Retable — prior 
to conservation