1. College of Electrical and Information Engineering, Hunan University, Changsha, China
2. Department of Geomatics Engineering, Changsha University of Science and Technology, Changsha, China
3. Department of Computer and Information Science, PAMI Research Group, University of Macau, Macau, China
4. Helmholtz-Zentrum Dresden-Rossendorf (HZDR), Helmholtz Institute Freiberg for Resource Technology, Freiberg, Germany