1. Dept. of Surveying and Geo-informatics Engineering, Tongji Univ., 1239 Siping Rd., Shanghai 200092, P.R. China; formerly, Key Lab of Advanced Surveying Engineering of State Bureau of Surveying and Mapping, 1239 Siping Rd., Shanghai 200092, P.R. China (corresponding author).
2. Dept. of Surveying and Geo-informatics Engineering, Tongji Univ., 1239 Siping Rd., Shanghai 200092, P.R. China.