1. School of Computer Software, Tianjin University, Tianjin 300072, China
2. Department of Computer Science and Engineering, Faculty of Engineering, The Chinese University of Hong Kong, Shatin 999077, Hong Kong
3. Open Laboratory of Geo-Spatial Information Technology and Application of Guangdong Province, Guangzhou Institute of Geography, Guangzhou 510070, China
4. Guangzhou Yuntu Information Technology Co., Ltd., Guangzhou 510665, China
5. Guangzhou Entry-Exit Inspection and Quarantine Bureau, Guangzhou 510623, China
6. School of Mechanical and Electrical Engineering, Guangzhou University, Guangzhou 510006, China