1. A method of correlating a two dimensional representation of a body to a three dimensional representation of the body comprising: i. acquiring a two dimensional image of the body; ii. generating a fitness function for the two dimensional image; iii. determining two dimensional outlines of the three dimensional representation of the body for a plurality of sets of three dimensional position and orientation values; iv. comparing the two dimensional outlines to the fitness function to generate measures of fit for each set of three dimensional position and orientation values; v. breeding new sets of position and orientation values using a genetic algorithm; and vi. repeating steps iii to v until the measure of fit converges to an acceptable solution.