1. College of Geodesy and Geomatics, Shandong University of Science and Technology, Qingdao, China
2. School of Geomatics and Marine Information, HuaiHai Institute of Technology, Lianyungang, China
3. State Key Laboratory of Mining Disaster Prevention and Control Co-founded by Shandong Province and Ministry of Science & Technology, Shandong University of Science and Technology, Qingdao, China