The normalised image of the absolute conic and its application for zooming camera calibration

We present a novel technique for calibrating a zooming camera based on the invariance properties of the Normalised Image of the Absolute Conic (NIAC). We show that the camera parameters independent of position, orientation and zooming are determined uniquely by the NIAC, and we exploit these invariance properties to develop a stratified calibration method that decouples the calibration parameters. The method is organised in three steps: i) computation of the NIAC, ii) computation of the focal length for each image, iii) computation of the orientation and the position of the camera. The method requires a minimum of three views of a single planar grid. Experiments with synthetic and real data suggest that the method is competitive with other state-of-the-art plane-based zooming calibration methods in the scenarios considered.