Photogrammetry provides a means for accurate measurement of archaeological features and artefacts through 3D recording and visualisation. The technique is based on the principal of stereo-photography where two images of the same subject are taken from slightly different positions. The different perspective apparent in each pair of images (stereo-pair) allows a 3D representation of the object or site to be recorded. Processing this information through computer software enables a wide range of visual data to be created including line drawings, contour plots, and 3D surface models.
A low-cost, non-intrusive method, developed for the NADRAP project by English Heritage in partnership with Loughborough University, was tested and enhanced by the project volunteers. This method, which was primarily based on research work previously undertaken on Australian rock art, enabled the volunteers to capture their own stereo-photographs using 'off-the-shelf' 5 megapixel resolution digital cameras.
Volunteers were then able to process these images using 'lower-cost' photogrammetry software (Topcon PI-3000) to produce a range of 3D images and surface models, with an accuracy of up to 1-3 mm. These models can be manipulated on screen and presented in different ways, enabling specific aspects of the rock art to be enhanced and studied. These include stripping off the surface texture to expose the geological and carved features more clearly, presenting the image as a contour model to accentuate the topography of the rock, and taking profiles through any plane of the rock to produce cross-sections of the carvings and rock surface.
The benefit of a 3D image is that it provides a more accurate and realistic model of the artefact or monument than conventional 2D recording techniques. The surface texture and topography of the rock, the relative depth of the carvings and the relationship between the carvings and natural geological features are faithfully replicated. As photogrammetry is a non-contact method, issues concerning the subjectivity of the recorder, repeatability of the record, and potential harm to the rock surface are all minimised. In addition, the ability to view the object in different ways precludes a single view-point perspective. Because the digital models are measurable, they provide considerable potential for comparative, quantified analysis of the carvings. With technology improving rapidly, these early results indicate that this technique has huge potential for accurate recording and monitoring of monuments and artefacts. Photogrammetry is highly recommended for specialists and amateurs.
Some of the most successful examples created by NADRAP volunteers can be seen in the Photogrammetry Gallery. Models of many of the panels recorded on ERA are also available for download: Search ERA for photogrammetry models.
Read more about photogrammetry:
Chandler, J.H., P. Bryan, & J.G. Fryer. 2007. The development and application of a simple methodology for recording rock art using consumer-grade digital cameras. The Photogrammetric Record. 22(117): 10-21.
Bryan, P.G & Chandler J.H, 2008. Cost-Effective Rock-Art Recording within a Non-Specialist Environment, Proceedings of ISPRS 2008, Beijing, China.