Xiangchao Zhang, born in 1982, is currently an associate professor at Fudan University, China. He is a member of ISO/TC 201, SPIE, ASPE, IEEE, and Shanghai Laser Society, respectively. He graduated from University of Science and Technology of China (USTC) in 2005 and received his PhD degree at Centre for Precision Technology, University of Huddersfield, UK in 2009. Dr Zhang's research interests include precision optical measurement, surface metrology and micro-optics. He has achieved a series of important results and published more than 60 papers. He has led several research grants including National Natural Science Foundation of China, Shanghai Natural Science Foundation, Aerospace Supporting Technology Foundation, etc.

Abstract
Complex functional components containing specially designed freeform surfaces or micro-structured surfaces are extensively employed in modern opto-electro-mechanical systems. The characterisation of these complex surfaces raises a great challenge to precision engineering. Stable fitting algorithms with different error metrics are developed for freeform surfaces. The bias caused by sampling density and assessment direction is analysed. In addition, the essential characterisation procedures of micro-structured surfaces, including edge-preserving filtration, region segmentation, feature recognition and morphology extraction are investigated systematically. The reliability and flexibility of the characterisation results are significantly improved.