a fourth frequency the sensor would not be useful for three dimensional position data but could be used to generate a signal indicating that it has moved out of position after the lg 12 is withdrawn another embodiment shown in fig1 utilizes multiple coils 22 the coils 22 are spaced apart along the length of the sheath 20 the coils 22 provide position data of various points along the length of the sheath 20 thereby u201c painting a picture u201d of the sheath as such even though the coils 22 are not providing 6 dof data when viewed together they provide an indication of the location and orientation of the sheath 20 hence this embodiment of sheath 20 may be used to both navigate to the target and provide a conduit for tools possibly obviating the need for the lg 12 referring now to fig2 there is shown an embodiment of a sheath 20 with a 6 dof sensor 30 incorporated into its distal tip 26 the sheath 20 is shown as transparent such that the details of the sensor 30 may be more easily displayed the sensor 30 includes three coils 32 34 and 36 coils 32 and 34 are angled while coil 36 is relatively circumferential to the sheath 20 preferably coils 32 and 34 lie in planes that are relatively perpendicular to each.