A Method for Accurately Measuring the Dimensions of Nearly Circular Planar Objects

A new system for determining the maximum and minimum radii of nearly circular two dimensional objects has been developed. The measurement uses a video camera and digitzer board to import a snapshot of the object. First, the pixels defining the contour of the object are traced. Then, a coordinate system transformation is performed and an iterative and adaptive least squares curve fitting algorithm is employed to extract the information of interest. Both the largest and smallest radii can be estimated with an accuracy of better than 0.1%. Completion of the measurement requires less than 4 seconds using a fast personal computer. Details of both the algorithm and the physical system are investigated with an emphasis on developing a measurement that is optimal in terms of both speed and accuracy. Results from simulations of the algorithm as well as actual measurements from a real life application will be presented.