It is often desirable to define objects with respect to images of an anatomydisplayed using an image guided surgery system. For non-trivial objects, orthose with complicated two or three dimensional forms, it may be difficult topresent information in a manner that is simple for a user to understand. Thelocal distance to a surface of interest, such as the surface of the definedobject, or to a desired position, the local penetration distance of thesurface of interest, or haptic repulsion force, often provides the most usefulinformation for augmenting the interaction of the user with the image guidedsurgery system. The scalar value of the local distance may be conveyed to theuser by visual, audio, tactile, haptic, or other means.
