1. Department of Surveying and Geoinformatics, Nanjing University of Posts and Telecommunications, Nanjing, China
2. School of Surveying and Land Information Engineering, Henan Polytechnic University, Jiaozuo, China
3. Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai, China
4. Department of Electronics and Telecommunications, Politecnico di Torino, Torino, Italy