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The Application of Digital Photogrammetric Techniques and Aerial Photography to the Preservation of Archaeological Detail.

1 Introduction

Digital photogrammetry is being adopted throughout the mapping industry because of the ease with which it may be applied to small and large-scale studies to generate both accurate and repeatable analyses and user-friendly visualisations of large datasets. For example, the detailed surveying of an archaeological site can produce significant amounts of spatial data including the geographical co-ordinates of the site, it's extent, the position of objects of interest and their dimensions. This is routinely represented on a surveyed map with associated scales. The process of surveying even a small site and generating accurate maps is labour-intensive. Digital photogrammetric techniques can be applied to aerial photographs of such a site to generate the same information in a fraction of the time and generates data sets and images that are readily transferred to other software packages, incorporated into reports and presentations and posted to WWW sites. Furthermore, aerial techniques may be applied in regions where access is limited or detailed examination of the site may cause damage to delicate artifacts.

The rapid development of digital photogrammetry and photogrammetric workstations in the last decade, and more so the increased availability of these systems to research establishments presents an extremely powerful tool to researchers in all spheres. This technique, using modern computing systems, is applicable at all scales of observation from the processing of satellite-acquired images to electron photomicrographs. The power of the technique lies primarily in the ease with which large amounts of data can be generated and recorded to a very high degree of accuracy in readily accessible formats. Additionally, the ease of data generation, representation and storage facilitates later cross-referencing of image derived data with subsequently recorded datasets of the same area. It is therefore possible to measure the change in terrain quantitatively through time and the changes determined can be ascribed to particular processes depending on their degree and style.

Aerial photography presents the most rapid method of image acquisition for medium-sized (metres across) and large-scale archaeological sites. The main benefits of such a survey are:

  • Image acquisition and processing of the entire area of interest is rapid and non-destructive.
  • Photogrammetric techniques can be employed to give a high degree of accuracy.
  • Ground surveying is minimal.
  • A single user can carry out all of the image processing, analysis and output on a single system.
  • The technique is ground-condition independent.
  • The technique can be rapidly repeated at specified time intervals and data sets easily archived for later comparison.
  • The final products are readily transferable to other software packages.

This case study will elucidate the power and ease of use of digital photogrammetry and image processing techniques in the recording and processing of data from a Bronze Age stone circle complex recently excavated in Northern Ireland: the Copney Stone Circle Complex. This site was chosen for examination using this technique because it presents unique problems to routine surveys. Specifically:

  • The complex nature of the site, with large numbers of stones of highly variable dimensions and arrangements within each stone circle requires very detailed and time-consuming ground surveying.
  • The use of aerial photos avoids the highly detailed ground-based photographic techniques normally employed on sites comprising such small artifacts.
  • The subject area is situated in waterlogged peat bog. This makes access by any vehicles impossible and manipulation of heavy surveying apparatus difficult.

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