The disclosure pertains to an apparatus comprising a circuitry. The circuitry is configured to obtain a calibration image of a target, to derive a sparse image based on the calibration image, wherein the sparse image includes image points, to derive ray support points based on the image points by performing an image to target mapping of the image points based on a polynomial function, wherein the ray support points being indicative of light rays reflected by the target and incidenting on an image sensor, and to generate a camera model based on the derived ray support points.