Using digital photogrammetry to produce 3D models at prehistoric ditched enclosures: Perdigões as a case study

The Perdigoes archaeological complex (Reguengos de Monsaraz, Portugal) is a prehistoric site near the Guadiana River, comprising at least 12 ditched enclosures, several hundred pits, an area with megalithic tombs and a set of standing stones (cromeleque). It is located in one of the richest archaeological landscapes of Iberia, with notable examples of Prehistoric monumental architecture such as menhirs and portal tombs (antas). A team from the University of Malaga (Spain) has been carrying out fieldwork in collaboration with the Portuguese entity ERA Arqueologia at the site since 2008. This includes geophysical (2008-2009) and micro-topographical (2011) surveys of the whole site, as well as both open-area excavations (2012-2013) and trenches (2009-2010, 2013) in the area surrounding Entrance 1. Digital photogrammetry is an inexpensive computerised method that enables the creation of three-dimensional models from photographs using image pattern recognition. The technique can be employed during the process of excavation to better record the archaeological evidence, to generate 3D models of the stratigraphical units and to digitalise singular findings. It is also useful for activities aiming to spread knowledge and awareness about the site. In this paper we will describe the basics of the method and its workflows, and three specific applications at Perdigoes. Later, we will briefly compare digital photogrammetry with alternative solutions for the digitalisation of cultural heritage, such as LIDAR and total station scanners with LASER.