1. Area of Cartographic, Geodesic and Photogrammetric Engineering, University of Oviedo, 33600 Mieres, Asturias, Spain
2. Institute of Natural Resources and Spatial Planning (INDUROT), University of Oviedo, 33600 Mieres, Asturias, Spain
3. Department of Physics, Polytechnic School of Mieres, University of Oviedo, 33600 Mieres, Asturias, Spain