Archaeological trace extraction by a local directional active contour approach

Archaeological trace extraction in aerial or satellite data is a difficult issue for automatic algorithms due to the traces similarity to other image artifacts or to their poor boundary information, discontinuities and so on. We propose in this paper a modified region based active contour approach for archaeological trace identification that overcomes the limits of standard methods of region uniformity and different consistencies with respect to the background. The proposed approach introduces a directional energy model in the minimization of the conventional energy term used in the existing active contour approaches. The local trace direction is estimated automatically after an initial unconstrained evolution of the region. Then, an iterative block based directional procedure has been introduced to limit the application of the modified method to local and adjacent areas and to allow the processing of large images in which the traces may have complex intersections or follow a curved trajectory. Finally, in order to reduce the initialization dependance problem, we propose the use of one seed point for each trace as the initial curve. Tests on the extraction of archaeological traces such as centuriations and ancient roads, visible as crop marks, have demonstrated that the proposed method and the developed MATLAB-based Graphical User Interface (GUI) facilitate unskilled/semi-skilled users in their archaeologic traces mapping operations and improve their detection precisions. (C) 2012 Elsevier Ltd. All rights reserved.