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The Effect Of Base To Focal Length Ratio On Stereo Rig Calibration Using A Planar Constraint Facility

Last Update2017-03-06
TitleThe Effect Of Base To Focal Length Ratio On Stereo Rig Calibration Using A Planar Constraint Facility
Author(s)Author #1
Author title:
Name: Mohammed Taleb Obaidat
Org: Professor of Civil Engineering, Jordan University of Science and Technology (JUST), Irbid, P.O. Box 3030, Jordan

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Contact AuthorAuthor #1
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KeywordsCamera configuration, Camera calibration, Focal length, Scale, Base, Off-the-shelf vision systems, CCD-cameras, Planar constraints, Lens distortion
AbstractThe effect of camera configuration; namely the base/focal length (b/f) ratio, on camera calibration parameters of a planar constraint facility was investigated. A planar calibration facility with 378 points 10 cm apart was constructed. A rolling platform that permitted variable base of stereo camera configuration, using one camera or two, was also designed. However, one camera was used for the stereo configuration utilized in this research work. Combinations of 11, 16, 25 and 45 mm focal settings and 40, 60 and 80 cm bases were used. This produced a range of b/f ratio ranging from 8.9 to 72.7. A mathematical algorithm and a software package were developed to calibrate hand-held Charge-Coupled-Device (CCD) cameras using a planar facility with fourdistance control. A parametric study was carried out to investigate the b/f ratio effect on calibration parameters. Propagation of variance and covariance of unknown residuals of image point and control distance computations, least-square mathematical model efficiency and potential accuracy of 3-D measurement computations were used to investigate the efficiency of this study. Experimental results showed that using b/f ratio between 20 and 70 was the optimal mapping configuration that had the capability of modelling the entire interior geometry of camera lens and plane coefficients accurately, as well as precisely computing the standard deviation of unknowns. Increasing the b/f ratio would produce a shift and instability in the principal point, a decrease in the affine scaling parameter and stability in the decentering distortion parameters and number of iterations. Increasing the camera base at constant focal setting would decrease the standard deviations of calibration parameters and increase reliability of the computed 3-D coordinates.
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