Camera calibrating apparatus and method

A camera calibrating apparatus for use with a laser source capable of generating a beam of coherent light defining a calibration plane, said camera being characterized by intrinsic imaging parameters and a field of view in the direction of an optical axis forming a predetermined angle with said calibration plane, said beam intersecting the field of view of said camera to define an object imaging area, said apparatus comprising:

• a calibration target including:
• a frame defining a coplanar arrangement of more than five reference points having known position coordinates within an object reference system associated with said frame and defining at least two dimensions, said frame being capable of being disposed in a camera calibration position wherein said coplanar arrangement of reference points is substantially parallel to said calibration plane;
• and
• an arrangement of light reflecting members protruding from said arrangement of reference points in a direction substantially perpendicular thereto so as to extend within said object imaging area when said frame is disposed in said camera calibration position to allow said camera to capture an image formed by illuminated portions of said light reflecting members;
• and
• image processor means for estimating position coordinates of said illuminated portions within an image reference system associated with said camera, for associating the estimated position coordinates of each said illuminated portion within said image reference system with the known position coordinates of a corresponding one of said reference points in relation with a corresponding one of said calibration planes within said object reference system, for calibrating a camera model based on said intrinsic imaging parameters with said associated known position coordinates and estimated position coordinates, and for using said calibrated camera model to associate any position coordinates in said object reference system with corresponding position coordinates in said image reference system.

A method of calibrating a camera characterized by intrinsic imaging parameters and a field of view in the direction of an optical axis, said method comprising the steps of:

• i) generating a beam of coherent light defining a calibration plane;
• ii) disposing said camera so that its field of view in the direction of its optical axis forms a predetermined angle with said calibration plane and so that said beam intersects the field of view of said camera to define an object imaging area;
• iii) providing a calibration target including:
• a) a frame defining a coplanar arrangement of more than five reference points having known position coordinates within an object reference system associated with said frame and defining at least two dimensions;
• and
• b) an arrangement of light reflecting members protruding from said arrangement of reference points in a direction substantially perpendicular thereto;
• iv) disposing said frame in a camera calibration position wherein said coplanar arrangement of reference points is substantially parallel to said calibration plane so that said light reflecting members extend within said object imaging area;
• v) generating with said camera an image formed by illuminated portions of said light reflecting members;
• vi) estimating position coordinates of said illuminated portions within an image reference system associated with said camera;
• vii) associating the estimated position coordinates of each said illuminated portion within said image reference system with the known position coordinates of a corresponding one of said reference points within said object reference system;
• viii) calibrating a camera model based on said intrinsic imaging parameters with said associated known position coordinates and estimated position coordinates;
• and
• ix) using said calibrated camera model to associate any position coordinates in said object reference system with corresponding position coordinates in said image reference system.