1. College of Automation Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 211106, China
2. Laboratory of Advanced Laser Technology of Anhui Province, Hefei 230037, China
3. Department of Photogrammetry and Remote Sensing, Finnish Geospatial Research Institute, 02150 Espoo, Finland
4. School of Computer Science and Engineering, Nanjing University of Science and Technology, Nanjing 210094, China