Automatic Approach for Calibrating Off-the-shelf Digital Cameras

Recent developments of digital cameras in terms of size of Charged Coupled Device (CCD) arrays and reduced costs are leading to their applications to traditional as well as new photogrammetric, surveying, and mapping functions. Digital cameras, intended to replace the conventional film based mapping cameras, are becoming available along with many smaller format digital cameras capable of precise measurement applications. All such cameras require careful assessment to determine their metric characteristics, which are essential to carry out photogrammetric activities. These characteristics include estimates of the calibrated focal length, location of the principal point relative to the array coordinate system, lens distortion, and the short and long-term stability of these quantities. These characteristics are known collectively as the Interior Orientation Parameters (IOP). Current calibration methods are based on traditional test fields with numerous distinct targets, which have to be professionally surveyed prior to the calibration procedure in order to precisely determine their three-dimensional coordinates. Establishing, surveying, and maintaining traditional calibration test fields are very expensive and not easy tasks for non-photogrammetric users of digital cameras. This paper relates to the development of a new laboratory calibration procedure that requires an easy-to-establish calibration test field (group of straight lines). In addition, the whole calibration process can be automatically carried out with minimal human interaction. It is expected that this calibration procedure would provide a good tool for studying the short and long-term stability of off-the-shelf digital cameras. In addition, it will give a great push to using those cameras in large scale mapping applications as well as various close range photogrammetric activities.