1. Department of Telematics Systems Engineering, Universidad Politécnica de Madrid, Avenida Complutense n° 30, 28040 – Madrid, España. E-mails: bbordel@dit.upm.es, diego.sanchezderiveracordoba@gmail.com, diego.martin.de.andres@upm.es, tomas.robles@upm.es
2. Department of Topographic Engineering and Cartography, Universidad Politécnica de Madrid, Campus Sur, 28031 Madrid, Spain. E-mail: ramon.alcarria@upm.es