1. Department of Civil, Environmental & Geomatic Engineering, University College London, Chadwick Building, Gower Street, London WC1E 6BT, UK
2. UCL Institute for Sustainable Heritage, Central House, 14 Upper Woburn Place, London WC1H 0NN, UK
3. Department of Conservation and Scientific Research, British Museum, Great Russell Street, London WC1B 3DG, UK
4. Philips Research Eindhoven, High Tech Campus 34, Eindhoven 5656 AE, The Netherlands