1. School of Geodesy and Geomatics, Wuhan University, Wuhan, China
2. School of Computer Science and Technology, Harbin Institute of Technology, Harbin, China
3. Department of Electrical Engineering and the Institute of Communications Engineering, National Tsing Hua University, Hsinchu, Taiwan
4. State Key Laboratory of Information Engineering in Surveying, Mapping, and Remote Sensing, Wuhan University, Wuhan, China