A method and apparatus for determining, calculating, and/or viewing a trajectory. The trajectory can be displayed on a display relative to image data of a patient. A user can use the system to determine relationships between two or more trajectories that have been determined. The relationships can be within two dimensional, three-dimensional, or four dimensional space. The relationships can include distance, angle, etc. The relationships can also be determined between real time trajectories and stored trajectories, or combinations thereof.