1. School of Computer Science and Technology, Beijing Institute of Technology, Beijing 100081, China
2. Academy of e-Government, Beijing Institute of Technology, Beijing 100081, China
3. School of Civil Engineering and Architecture, Wuhan Institute of Technology, Wuhan 430074, China
4. State Key Laboratory of Information Engineering in Surveying, Mapping and Remote Sensing (LIESMARS), Wuhan University, Wuhan 430079, China