1. School of Computer Science and Engineering, Northwestern Polytechnical University (NWPU), Xi’an, Shaanxi 710072, China
2. School of Mechanical Engineering, NWPU, Xi’an, Shaanxi 710072, China
3. Center for OPTical IMagery Analysis and Learning (OPTIMAL), NWPU, Xi’an, Shaanxi 710072, China
4. School of Automation, NWPU, Xi’an, Shaanxi 710072, China