1. School of Computer Science and Technology, Nanjing University of Aeronautics and Astronautics, Nanjing, China
2. Fujian Key Laboratory of Sensing and Computing for Smart Cities, School of Informatics, Xiamen University, Xiamen, China
3. Shenzhen Research Institute, Nanjing University of Aeronautics and Astronautics, Shenzhen, China
4. Department of Geography and Environmental Management and Department of Systems Design Engineering, University of Waterloo, Waterloo, ON, Canada