3-D Shape Measurement Using Three Camera Stereopsis

Traditional stereopsis techniques involve using two cameras. When matching parts are identified in both images, the range of the matching parts is determined by triangulation. However, occlusions and missing parts in the two images have raised problems in determining correspondence. The use of three camera positions promises to reduce the occlusion and missing parts problems as well as to reduce the probability of incorrect matches. A relative calibration technique which determines the external parameters of the three cameras used is presented. With the cameras calibrated, feature points from images are selected so that matching parts can be easily identified. The edges in the three images are used as feature points. A trinocular matching technique using epipolar line constraints and line coherence constraints is used to find matching edges in the three cameras. With correspondences established in the images, the shape of objects can be obtained since camera parameters are known.