The Application of Close Range Photogrammetry for English Heritage Conservation Projects 
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• non-image based, such as hand and theodolite measurement but which now includes the developing area of direct 3D laser 
scanning 
• image based, such as rectified photography, panoramic imaging and photogrammetry. 
At this point it should be recognised that each technique has its own characteristics and merits that will influence its successful 
application within a project. For instance the type of data that is required, the time available to carry out the survey, the prevailing 
site conditions, the required accuracy of the data and, of course, the cost are all influential factors. Even though this last factor, cost, 
is often the over-riding factor in applying some of the more expensive techniques - such as photogrammetry - it should not be 
forgotten that an inappropriate application can result in a survey product that is devalued in the eyes of those who have to use it. 
Appropriateness of technique is therefore a key issue within English Heritage, not only to minimise data duplication and of course 
reduce project costs, but also to maximise value for money, long-term usability and production of an effective archive from the data 
source. Therefore we in English Heritage feel this should always be considered within any project undertaken and certainly before 
the use of one specific technique, such as close range photogrammetry is embarked upon. 
4. CLOSE RANGE PHOTOGRAMMETRY 
Metric Survey now includes the use of many survey techniques, each with their own characteristics and merits. Photogrammetry is 
but one of these, but one that in English Heritage has demonstrated for many years that for mass data capture, it is probably the most 
reliable technique currently available. Previously this has concentrated on two dimensional data capture, typified by the traditional 
outline drawing of building facades. However with ever more CAD and GIS platforms being used by those involved in the 
conservation process, and more 3D models being required for visualisation purposes, the accurate extraction of the third dimension 
has now become a critical element of the process. This has recently been recognised by inclusion of several paragraphs dedicated to 
the accurate extraction of 3D photogrammetric data within the Metric Survey Specifications for English Heritage. 
All photogrammetric applications typically used by English Heritage, from aerial down to close range, have previously relied upon the 
acquisition of stereophotography to form the base three-dimensional image of the object to be surveyed. As the technique is an indirect 
method of analysing the surface and shape of an object by directly measuring images of it, it was and still is this unique 3D view that has to 
provide the fundamental image from which all further measurements were taken. Within close range photogrammetry Metric Cameras, 
such as the Wild P31 still used by English Heritage, and photographic film have traditionally been used to provide as accurate an image, in 
terms of exposure and geometry, as was technically and economically feasible. However this close range market has never been 
sufficiently large enough for the manufacturers to justify mass production of such cameras. Therefore they have always remained large, 
cumbersome devices, relatively devoid of the additional features typically seen on the average SLR camera and worst of all, very 
expensive - a new metric camera can cost anything from £15,000 ($24,000) upwards. Hence it is encouraging to see that within the general 
transition over to digital imaging a change to more commercially available cameras and camera backs is developing with the emphasis not 
just on physical size but resolution of image. Cameras with mega-pixel resolution are 
now becoming commonplace in the sub £500 ($800) price range whilst the higher 
resolution professional market is now down to the £5000 ($8000) level due principally to 
recent competition between Kodak and Nikon. In terms of close range photogrammetry, 
the development now appears to be towards the medium rather than the traditional large 
format market. Therefore it is here that English Heritage have recently committed 
themselves to direct digital image capture in the field by obtaining one of the new Kodak 
DCS Pro Digital Backs, for initial use with a Mamiya RZ67 medium format camera. 
Even though the equipment has just been acquired, and no projects have actually been 
carried out to date, it is hoped the 16 mega pixel (4080x4080) sensor will now satisfy our 
requirements for image resolution, whilst providing a valuable insight into other 
technicalities such as accurate colour management and digital image archiving. It is also 
hoped this digital revolution may lead to a reduction in survey costs within the 
specialised close range fields of architecture and conservation, where cost is often the 
deciding factor in applying photogrammetry or whether to ‘make do’ with a lesser but 
cheaper product. However in order to survive, photogrammetry may simply have to 
merge with the up and coming technology of 3D laser scanning, which is quickly finding 
its way into the close range market with its ability to rapidly record detailed data clouds 
of objects in near real time. 
5. DIGITAL IMAGE PROCESSING 
When in 1994 English Heritage first investigated the application of digital 
photogrammetry within one of its own conservation projects, the standing stones of 
Stonehenge, there were very few digital photogrammetric workstations commercially 
available. Those that were, were very expensive at around £250,000 ($400,000) but 
since then increased competition and a move towards using standard PC-based 
computer hardware has lead to costs falling significantly so that similar equipment can 
now be purchased for around l/5 th of the price. Equipment, such as the Helava Digital 
Photogrammetric Workstation used by English Heritage, is now based around a 
standard computer platform albeit high end in terms of 3D image display and storage 
capacity. Yet it still combines a lot of processing capability and functionality that 
provides useful features for close range projects such as: Photoerammetric Workstation