A Method to Assess Spatial Coordinates in Art and Archaeological Objects: Application of Tomography to a Dolmen

Abstract A method to determine the values of spatial coordinates of bodies, specifically adapted to study art and archaeological objects, was developed and tested on a dolmen made of granite in north-west Spain. This method, based on geometric principles, comprises an easy-to-assemble rigid structure as a physical support, and software based on the algorithms discussed below, which together provide a rapid and inexpensive means of assessing coordinates. One of the main features of this procedure is the ability to quantify the accuracy of the coordinates being calculated according to the quality of the input measurements. The simplicity of obtaining data means that the method can even be performed upon rough and irregular-shaped objects, and in zones where other instruments are difficult to handle; for example, the interior of dolmens or small cavities. A demonstration of the method was performed upon an upright stone of a megalith in north-west Spain (Axeitos Dolmen, La Coruna). The coordinates of many points of measurement surrounding the object, combined with parameters from ultrasonic signals, were used to achieve three-dimensional tomography. Considering the experimental errors produced by different operators, the accuracy achieved when estimating the coordinates was better than 1 cm. The tomograms obtained have been employed to assist in the evaluation of damage to this megalith.