1. a Department of Geography & Environmental Management , University of Waterloo , Waterloo , Ontario , Canada , N2L 3G1
2. b School of Information Science and Engineering , Xiamen University , Xiamen , FJ , 3610005 , China
3. c Department of Civil Engineering , Ryerson University , Toronto , Ontario , Canada , M5B 2K3
4. d School of Geodesy & Geomatics , Wuhan University , Wuhan , 430079 , Hubei , China
5. e School of Remote Sensing & Information Engineering , Wuhan University , Wuhan , 430079 , Hubei , China
6. f Unit 63961 , Beijing , 100012 , China