1. Professor, Ruhr-Univ. Bochum, Geodesy in Civil Engineering, Geb. IA 4/49, Bochum 44780, Germany (corresponding author).
2. Associate Professor, Doctor in Engineering in Geodesy and Cartography, Dept. of Cartographic Engineering, Polytechnic Univ. of Valencia, Geodesy and Photogrammetry, Cº de Vera s/n, Building 7i, Valencia 46022, Spain.