1. School of Geological Engineering and Geomatics, Chang’an University, Xi’an 710064, China
2. Institute of Geography and Geoecology (IFGG), Karlsruhe Institute of Technology (KIT), 76131 Karlsruhe, Germany
3. College of Geomatics, Xi’an University of Science and Technology, Xi’an 710021, China
4. Key Laboratory of Coal Resources Exploration and Comprehensive Utilization, Ministry of Natural Resources, Xi’an 710054, China
5. Institute of Surveying and Mapping, Xi’an 710054, China