Three-dimensional modelling of archaeological sites using close-range automatic correlation photogrammetry and low-altitude imagery

摘要

Photogrammetry is a commonly used technique in three-dimensional image-based modelling for cultural heritage documentation. Three-dimensional image-based techniques that combine close-range photogrammetry and automatic image matching are presently attracting a great deal of interest. This paper evaluates the feasibility of the application of photogrammetric three-dimensional modelling of an archaeological site with close-range automatic image-matching software and a consumer-grade digital camera. In order to correctly model upward-facing surfaces using this technique, the photographs were taken from the air with the camera in low-oblique position. A mast pole was used as camera platform to obtain low-altitude imagery. To verify the usefulness of this method it was applied to the hill fort 'Castro de Formigueiros', located in Lugo, Spain. In this case, low-cost automatic image-correlation photogrammetry has proved to be a powerful, cost-effective and versatile technique for the documentation, analysis and cultural dissemination of archaeological mapping. The mast used is inexpensive, easily transported and handled on site, and allows oblique photographs of the ground and wall-tops to be obtained at distances similar to photographs of vertical wall faces taken from the ground. As a result, the resolution and accuracy of the point clouds of all the surfaces of the final model are similar. Given the geometric peculiarities of hill forts (the occupied surface area, height, volume and distribution of the objects) and the relief (they are generally located in areas difficult to access and often on high ground), the mast is particularly suitable for photographing low-altitude imagery at archaeological sites, as the final accuracy of the three-dimensional model demonstrates. The tools that have been applied to the final digital model of the hill fort show the information analysis potential that can be obtained for archaeological work.