for computation of a composite image including a synthesized image of a surgical instrument; [0044]FIG. 13 is a detailed flowchart of trajectory replanning and fixture alignment; [0045]FIGS. 14a-c illustrate a navigational view display and corresponding planar segments through a body; [0046]FIGS. 15a-f illustrate a ???field of view??? display and corresponding conical section through a body; [004