for each channel lastly the field of vision fov can be determined based upon the number of visible annuli when the camera to chart distance and chart size is known this is represented at step 550 it should be understood that although all of the steps in fig5 are depicted as occurring sequentially many of the steps can be performed in a variety of orders as would be understood by those of skill in the art the process of perspective mapping is accomplished in accordance with the following formulae given a point x u03b5 r 2 the perspective correction mapping with a tilt vector u03c4 u03b5 r 2 is defined by u03c0 u03c4 u2061 x 2 u2062 x k u2062 b 0 k u00b7 n u03c4 x k u00b7 n u03c4 k x x 1 x 2 0 n u03c4 u03c4 1 u03c4 2 1 uf603 u03c4 1 u03c4 2 1 uf604 k 0 0 2 b 0 0 0 1 f u2061 p _ r _ x 0 x c u03c4 u2211 k j u2062 u2062 uf603 d u2061 u03c0 u03c4 u2061 p kj x 0 u2062 u03c0 u03c4 u2061 p kj x 0 uf603 u03c0 u03c4 u2061 p kj x 0 uf604 x 0 x c uf604 r.