Gas holder base 1893, Liverpool UK

Photomodelling: presenting the third dimension

Peter Rauxloh

Following on from a previous blog exploring the availability of photogrammetry software capable of creating maps and models from overlapping photographs taken using Small Unmanned Aircraft, this blog considers the application of the same software to ground based imagery.

Digital photogrammetric software such as Agisoft Photoscan, Pix4D and others, is becoming increasingly popular amongst archaeologists because of the speed and accuracy with which complex 3D objects can be modelled, and the ability of these models to convey that complexity. The software performs photogrammetric processing of highly overlapping digital images, to generate 3D spatial data, and is innovative because it can process images taken with a standard digital camera, it is a simple process and it is rapid. 

Such software and specifically its implementation of various computer visualisation techniques, such as structure from motion and dense stereo-reconstruction, has effectively re-invigorated the powerful technique of metric photographic survey by lowering the barrier of entry to its use.

This photo modelling approach operates using images of a target between which there is a great deal of overlap; the ability to model a target is therefore not a function of size. It has been used to monitor the minute deformation of buildings and boats, and to display small prehistoric metal objects.

At MOLA we have used it to create models of objects such as an iron and wood  bucket from the rich Anglo Saxon Burial chamber near Prittlewell in Essex, building complexes such as a late 19th-century siphon pit from Macclesfield in Derbyshire and indeed whole excavations, such as those from Gordon House, London.

It is self-evident that it is easier to  appreciate a  3D object when it is  viewed in three dimensions, and the software is allowing archaeologists to communicate far more effectively in this respect. Equally, being built on the framework of a metrically accurate 3D point cloud, these models provide relaible quantitative data such as height, witdh or volume, and allow for the generation of profiles and sections and other more traditional 2D products.

Please contact Dr. Peter Rauxloh if you would like to know more about MOLA's work in this area.

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