1. Xi’an Institute of Optics and Precision Mechanics, Chinese Academy of Sciences, Xi’an 710119, P. R. China
2. School of Electronic and Information Engineering, Xi’an Jiaotong University, Xi’an 710049, P. R. China
3. University of Chinese Academy of Sciences, Beijing 100049, P. R. China
4. State Key Laboratory of Virtual Reality, Technology and Systems, Beihang University, Beijing 100083, P. R. China
5. School of Automation Science and Electrical Engineering, Beihang University, Beijing 100083, P. R. China