GEOMETRIC CALIBRATION OF CCD CAMERA USING PLANAR OBJECT

A method of geometric calibration of charge-coupled device (CCD) visio n systems for metric measurement has been developed. The method does n ot require a special calibration facility or accurately surveyed three -dimensional (3D) control points. It only requires that one stereo pai r of images of a planar object be acquired with the CCD camera that is to be calibrated. Using a planar wall constraint as a control, the st udy identified that a priori knowledge of seven parameters of interior orientation could be used to effectively model the interior geometry of known focal length CCD cameras equipped with zoom lenses. Brick wal ls provided an excellent calibration source of such a calibration faci lity, because they can provide a sufficiently large number of well-def ined points throughout the stereo images at almost any focal setting. The corners of the bricks and mortar joints might be used as target po ints. Comparison with laboratory calibration using a 3D test field sho wed that the method of planar constraint was capable of providing resu lts of comparable accuracy at 10-32 mm variable focal settings lens, a nd potentially even better results at larger focal settings. A root-me an square (RMS) error of better than +/-0.2 pixels was achieved consis tently for higher values of focal setting. Using about 40-50 stereo im age points, the interior geometry of the CCD camera was effectively mo deled. Increasing the number of image points increased the stability o f the calibration parameters. The method has the potential to be advan tageous in terms of practicality, availability and economy; time savin g, and providing a large number of image points.