1. a School of Geomatics and Urban Information, Beijing University of Civil Engineering and Architecture , Zhanlanguan Road, Xicheng District, Beijing, 100044, PR China
2. b State Key Laboratory of Remote Sensing Science, Jointly Sponsored by the Institute of Remote Sensing Applications of Chinese Academy of Sciences and Beijing Normal University, Institute of Remote Sensing Applications, Chinese Academy of Sciences , PO Box 9718, Beijing, 100101, PR China
3. c Department of Computing , London Metropolitan University , 166-220 Holloway Road, London, N7 8DB, UK