1. ETSI Topografía, Geodesia y Cartografía, Universidad Politécnica de Madrid (UPM), 28031 Madrid, Spain
2. Geological Survey and Mining Institute of Spain (CN IGME-CSIC), Rios Rosas 23, 28003 Madrid, Spain
3. Geomatics Research Unit, Centre Tecnológic Telecomunicacions Catalunya (CTTC/CERCA), 08860 Castelldefels, Spain