1. School of Computer Science and Engineering, Shanxi Key Laboratory for Network Computing and Security Technology, Xi’an University of Technology, Xi’an, China
2. Department of Geography and Spatial Information Techniques, Ningbo University, Zhejiang, Ningbo, China
3. School of Software, Shanxi University of Science and Technology, Xi’an, China
4. Faculty of Electrical and Computer Engineering, University of Iceland, Reykjavik, Iceland