1. Zhongnan Engineering Corporation Limited, Power China, Changsha 410014, China
2. State Key Laboratory of Information Engineering in Surveying, Mapping and Remote Sensing, Wuhan University, Wuhan 430079, China
3. College of Architecture and Urban Planning, Hunan City University, Yiyang 413000, China
4. Department of Geodesy and Geoinformation, TU Wien, A-1040 Vienna, Austria