1. Ph.D. Student, Dept. of Engineering, Univ. of Cambridge, Cambridge CP2 1PZ, U.K. (corresponding author).
2. Lecturer in Computer Vision and Learning, Dept. of Electrical and Electronic Engineering, Imperial College London, London SW7 2AZ, U.K.
3. Lecturer, Faculty of Engineering, Thammasat Univ., Pathumthani 12120, Thailand; formerly, Ph.D. Student, Dept. of Engineering, Univ. of Cambridge, Cambridge CP2 1PZ, U.K.
4. Professor of Information Engineering, Dept. of Engineering, Univ. of Cambridge, Cambridge CP2 1PZ, U.K.
5. Professor of Civil Engineering, Dept. of Engineering, Univ. of Cambridge, Cambridge CP2 1PZ, U.K.