CALIBRATING A LENS WITH A “LOCAL” DISTORTION MODEL
This paper is about camera calibration where an abnormal systematic effect was discovered. The effect was first encountered in a multi-camera system used for close range 3D photogrammetric reconstruction. The objectives for this research were two-fold. The first objective is to identify the source of the systematic error, and the second objective is to model the error as rigorously as possible. The first objective was met after acquiring several calibration data sets where the camera bodies, the lenses, and the image formats were varied. It was concluded that the source of error is the lens system. The second objective was also met. The so called “local” lens distortion was modelled using second order polynomials as the plots of the residuals vs. the image coordinates resembled parabolic shapes. Overall, the final room mean square error for the residuals after applying radial and “local” lens distortion was reduced from 1/2 to 1/6 of a pixel or a 200% relative estimated error improvement.