A Method for Elliptical Light Spot Image Recognization in Vision Coordinate Measuring System

A light-pen single camera 3D coordinate vision measurement system is introduced, Based on the analysis of the system´s image characteristics, a digital method, which is for recognizing the elliptical light spot images of the measured control points, is proposed. Compared with the pixel number of the measured control points´ elliptical light spot image, the too large and small light spot images can be eliminated. Then, all the tracked contour points are fitted into a ellipse curve, and the center, the length of axle and rotation parameters of the ellipse are obtained. If the elliptic parameters are unreasonable, such as the center outside the ellipse or the length of axis is too long or too short, etc., the contour also must be erased. Otherwise, the elliptical profile error of the contour is calculated. At last using the method based on the evaluation for elliptical profile error, the measured control points´ elliptical light spot image can be recognized. The algorithm for this method is given, and the experimental result shows that this algorithm is simple, fast, easy to be realized and practical to the vision inspection system with circular measured control points.