Earlier in the year we were commissioned by Paul Frodsham of the North Pennines AONB under the guise of the Heritage Lottery funded Altogether Archaeology project to undertake two types of photogrammetric survey at Long Meg and Her Daughters stone circle located in the Eden Valley, near Penrith, Cumbria. This was part of a wider community project to develop an understanding of this exceptionally important monument and provide detailed surveys and geophysical investigation of the monument.
The work was undertaken in March 2013 and this post is concerned with the first part of our input into the investigation, which was producing a detailed aerial photographic plan of the site using a quadcopter UAV (Unmanned Aerial Vehicle).
This method uses aerial photographs taken from a small electrically powered model helicopter (UAV) which has the ability to carry a light weight camera and has the advantage that it can take photographs from much lower altitudes than can legally be achieved with a light aircraft. Survey control was introduced to the photographs by the placement of survey control targets across the site which were located by means of a survey grade GPS.The photogrammetric processing was undertaken using Agisoft software that provides detailed modelling using the overlap of up to 150 photographs, and creates a very detailed DTM (Digital Terrain Model) across the site. The photographs were then digitally draped over the model to create an accurate 3D model of the ground surface.
The primary output, however, was an accurate flat two dimensional image which can be used to generate accurate plans of surface archaeological features and contours across the extent of the site (at the top of the post). However, the 3D model can also be output as a tool to visualise the site from any perspective and can be viewed in more recent versions of Adobe Acrobat as a 3D pdf file.
Many thanks should go to all of the Altogether Archaeology volunteers who turned up in the cold weather to work on site during the project.