The Application of Photogranimetric Survey ... the Great Ceiling at Peterborough Cathedral 
97 
successful procurement by the Dean and Chapter themselves, of the next phase of base photogrammetry through the commercial 
sector and the data is already being used by the conservators on site. 
5. THE USE OF ORTHOPHOTOGRAPHIC IMAGES 
As noted earlier, little of the painted detail was recorded as line work. Instead, a scaled photographic image was to be utilised and it 
is here that the application of digital photogrammetric techniques, and the introduction of the digital orthophotograph, was to become 
crucial to the documentation part of the project. 
The Photogrammetric Unit already had experience of digital photogrammetry through the survey of the standing stones at 
Stonehenge in Wiltshire. As with this survey, the original colour negatives were scanned at 22.5 micron resolution, using a Zeiss PS1 
photogrammetric scanner, yielding fdes of around 120MB each. These were imported into a Helava DPW770 digital workstation, 
running SOCET Set software, and processed to form a complete digital orthophotograph (Fig. 6) of the entire ceiling at 5mm 
resolution and a file size of 90MB. 
Figure 6. Unformatted version of the complete orthophotographic survey processed at 5mm resolution 
Considering the use of detail points only for the survey control, and the observation and photography over a 25m range, the errors 
achieved during the orientation of each of these models were deemed perfectly acceptable for the production of an orthophotograph - 
mean RMS errors of the X, Y and Z co-ordinates of the 87 control points were 3.4mm, 6.0mm and 11.6mm respectively. 
Extracts from this complete orthophotograph have since been provided, in digital form, to the conservators working directly on the 
ceiling (Fig.8). 
Using CorelDRAW these images have been imported into their own site based computers located on the scaffold platform above the 
nave, to provide a full colour backdrop to the outline line drawings, previously supplied and imported via DXF format. 
• Nail Holes 
■ Insect damage (stable) 
™ Insect damage (unstable) 
■ Split wood (unstable) 
™ Spirt wood (stable) 
™ Surface splintering 
W Shot Damage 
FIGURE No: 
Kmm PANEL No 37/II 
PETERBOROUGH CATHEDRAL - NAVE CEILING 
Conservation Programme Phase 1 (Jan ■ May 1998) 
: 1 
PRELIMINARY [otsawntON 
CONDITION survey j Ceiling Structure, Lower Side 
P*vo«Dgre«im**y СОиПИ» of I TT* р*«ту U*l0Oar PnlWI«« 
Enal«*i Hortteg* 5 Cta«* Ur», CWcptee «ОПОР 
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Figure 7: Extract from preliminary technical survey 
Figure 8: Conservator using base 
survey on site 
Additional details have then been measured on site and inserted into these base drawings prior to printing at an appropriate scale - in 
this instance 1:15 for immediate use on site (Fig.7). Together they have provided both this preliminary condition survey and the rest 
of the project with a completely new level of documentation.