1. Department of Land Surveying and Geo-Informatics, The Hong Kong Polytechnic University, Hong Kong, China
2. Research Centre for Artificial Intelligence in Geomatics, The Hong Kong Polytechnic University, Hong Kong, China
3. State Key Laboratory of Information Engineering in Surveying, Mapping and Remote Sensing, Wuhan University, Wuhan, China
4. Department of Computer Science, Stanford University, Stanford, CA, USA