A study of a priori knowledge-assisted multi-scopic metrology for freeform surface measurement

The traditional multi-scopic metrology system makes use of a micro lens array to capture a raw 3D-image of the target surface in a single snapshot through a CCD camera under normal illumination. However, the resolution of the system depends on the matching precision and efficiency of disparity information during the processing of the 3D raw data. In this paper, the a priori knowledge-assisted multi-scopic metrology is studied and an a priori knowledge-assisted multi-scopic metrology system is established which makes use of patterned illumination custom-designed based on the a priori knowledge of the target freeform surface profile. The a priori knowledge provides abundant versatile known information for a precise and efficient matching process so as to enhance the measuring performance. A customized disparity matching process based on the a priori knowledge is developed accordingly for high-resolution 3D surface reconstruction. An experimental study for measuring freeform surface is conducted to verify the feasibility of the proposed a priori knowledge-assisted multi-scopic metrology system through the comparison between that using normal illumination and a priori knowledge-assisted patterned illumination.