3-D Measurement of the Tips of the Line-Like Object using Shadow Information

Abstract

In order to measure the 3-D positions of wire tips a new vision system has been developed. The new method does not use any special method of projecting light. Distance information of any visible point on wire can be obtained from images of wires and their shadows on a working table projected from a point light source. A theory is presented to determine the 3-D geometry of wires from the image taken by a TV-camera with prior knowledge on arrangement of the environment: the camera, the table and the lighting source. Wires and their shadows are extracted as strips from an input image (a 256 by 256 4 bit digital picture) by applying thresholding and thinning operators. Correspondence between each wire and its shadow in image is established by examining coincidence of lines from end points of the strips to the light source in the image plane. Thus, 3-D positions of wires can be determined from the geometry of the environment. A vertically mounted camera and a horizontal table are used for the experiment, and the position errors for fine wires is less than one percent of the size of sight.
In this paper, we describe the principle, the procedure and calculation of the measurement. Finally, the experimental results are shown and discussions are given.