T. Pribanic (Croatia), P. Sturm (France), and M. Cifrek (Croatia)
camera calibration, 3D reconstruction, absolute conic
A very common and effective approach for 3D reconstruction is a camera based system where 3D information is extracted from images. Different systems involve different camera calibration methods/tools. Characteristically for many systems is to calibrate the cameras using a single wand of known length. As integral part of the calibration procedure, initial camera parameters are commonly computed by putting and imaging two or three orthogonal wands inside the working volume. This is usually followed by the second step: sweeping the working volume with a single wand of known length. This paper presents two alternative ways of initializing camera parameters using essentially the same calibration tools (orthogonal wands), however by sweeping the volume with an orthogonal pair or triad of wands instead of a single one. The proposed methods exploit the orthogonality of the used wands and familiar linear constraints to calculate the image of the so-called absolute conic (IAC). Extracted internal parameters values from IAC are closer to the refined ones, assuring faster and safer convergence. Even without refinement, sometimes not necessary, reconstruction results using our initial sets are better than using commonly obtained initial values. Besides, the entire calibration procedure is shortened since the usual two calibration steps become one.
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