Abstract
This paper proposes an improved calibration site design for reliable focus-dependent camera calibration in close-range photogrammetry. The proposed calibration site displays an adjustable checkerboard on a large liquid crystal display television (LCD TV), such that the same number of checker cells appear at the same position at any focusing distance. By adjusting the roll and pitch of the LCD TV bracket, various convergent angles were implemented in order to successfully conduct self-calibration. To obtain a greater depth of field and to facilitate reproducibility, the images were acquired using a small aperture from a camera that was firmly mounted on a distance-adjustable rail. The interior orientation parameters of the camera were estimated, and the estimation errors were assessed. The results revealed a flat error level for each focusing distance; thus, consistent reliability was achieved regardless of the focusing distance. Using the estimated parameters, a 3D measurement test was conducted, and the proposed method yielded 2% smaller root mean square error. The proposed method can be implemented easily and performs reliable and accurate focus-dependent calibration.
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