1. Dr.-Ing., Institute of Geodesy, Global Positioning System (GPS), Stuttgart Univ., Geschwister-Scholl-Str. 24D, 70174 Stuttgart, Germany (corresponding author).
2. Professor, Dept. of Surveying and Geo-Informatics, Tongji Univ., 1239 Siping Rd., Shanghai 200092, P. R. China.
3. Associate Professor, Dept. of Surveying and Geo-Informatics, Tongji Univ., 1239 Siping Rd., Shanghai 200092, P. R. China.
4. Professor, Institute of Geodesy, Stuttgart Univ., Geschwister-Scholl-Str. 24D, 70174 Stuttgart, Germany.