1. College of Geodesy and Geomatics, Shandong University of Science and Technology, Qingdao 266590, China
2. State Key Laboratory of Resources and Environmental Information System, Institute of Geographical Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China
3. University of Chinese Academy of Sciences, Beijing 100049, China
4. School of Geoscience and Technology, Zhengzhou University, Zhengzhou 450001, China