1. School of Environment and Spatial Informatics, China University of Mining and Technology, Xuzhou, China
2. Sichuan Institute of Coal Field Geological Engineering Exploration and Designing, Chengdu, China
3. Sichuan Institute of Coal Field Surveying and Mapping Engineering, Chengdu, China
4. Department of Land Surveying and Geo-Informatics, The Hong Kong Polytechnic University, Hong Kong