1. School of Geography Science and Geomatics Engineering, Suzhou University of Science and Technology, 99 Xuefu Road, Suzhou 215009, China
2. Research Center of BeiDou Navigation and Remote Sensing, Suzhou University of Science and Technology, Suzhou 215009, China
3. School of Surveying and Land Information Engineering, Henan Polytechnic University, Jiaozuo 454000, China
4. Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 200030, China