Xiangrong Xin, School of Surveying and Spatial Information, Shandong University of Science and Technology, Qingdao 266590, China, China; Hua Li, Ruibo Li, Aerospace Information Research Institute, Chinese Academy of Sciences, Beijing 100094, China, China; Lin Sun, School of Surveying and Spatial Information, Shandong University of Science and Technology, Qingdao 266590, China, China; Wang Dacheng, Aerospace Information Research Institute, Chinese Academy of Sciences, Beijing 100094, China, China