1. a Advanced Research Center for Spatial Information Technology, Department of Land Surveying and Geo-Informatics , Hong Kong Polytechnic University , Hong Kong
2. b Institute of Intelligent Vision and Image Information, College of Electrical Engineering and Information Technology , China Three Gorges University , Yichang, 4434002, China
3. c Electronic and Information Engineering Department , Huazhong University of Science and Technology , Wuhan, 430074, China