1. Associate Professor, College of Surveying and Geo-Informatics, Tongji Univ., Shanghai, 200092, China.
2. Ph.D. Student, College of Surveying and Geo-Informatics, Tongji Univ., Shanghai, 200092, China.
3. Professor, College of Surveying and Geo-Informatics, Tongji Univ., Shanghai, 200092, China (corresponding author).