In the process of measuring arc radius of workpiece by using binocular vision

detecting and matching of feature points of arc edge are very important. In order to detect the feature points of the workpiece arc

by improved random sample consensus（ RANSAC） algorithm

fit the ellipse

and screen edge feature points in the inner point; in order to match the feature points of workpiece arc

make epipolar lines corresponding to two images parallel by epipolar constraint

so that the scanning line characteristics can be satisfied. On this basis

the ellipse center is chosen as the matching reference point

and arc edge feature points are matched by line. After getting the matching points

the improved RANSAC algorithm is used to eliminate the mismatching pair. The reliability and accuracy of the method are verified by experiments.