1. College of Earth Sciences, Chengdu University of Technology, Chengdu 610059, P. R. China
2. Key Laboratory of Geoscience Spatial Information Technology of Ministry of Land and Resources (Chengdu University of Technology), Chengdu 610059, P. R. China
3. College of Tourism and Urban-Rural Planning, Chengdu University of Technology, Chengdu 610059, P. R. China
4. Geomatics Engineering Department, Sichuan College of Architectural Technology, Deyang 618000, P. R. China
5. Department of Land Surveying and Geo-Informatics, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong 999077, P. R. China
6. The Six Topographic Surveying Brigade of NASMG, Chengdu 610500, P. R. China
7. China Railway Eryuan Engineering Group Co. Ltd, Chengdu 610031, P. R. China