Geometric Modelling and Calibration of Fisheye Lens Camera Systems

The paper describes a geometric projection model for fisheye lenses and presents results of the calibration of fisheye lens camera systems based on it. For fisheye images the real projection model does not comply with the central perspective. In addition, the lenses are subject to considerable distortions. The fisheye lens projection follows an approximately linear relation between the incidence angle of an object point’s beam and the distance from the corresponding image point to the principle point. The developed projection model is extended by several distortion parameters. For the calibration of fisheye lens camera systems, a calibration room was created and equipped with number targets. They were arranged to have a good distribution all over the image. The reference object coordinates of the targets were determined with high precision. The calibration itself is done by spatial resection from a single image of the calibration room. The calibration parameters include interior orientation, exterior orientation and lens distortion. Besides the geometric model for fisheye lenses, the paper shows practical results from the calibration of a high quality fisheye lens on a 14 mega pixel camera as well as a consumer camera equipped with a fisheye lens.