Systems and methods for determining the state of motion of an instrument

A system may comprise an instrument with an elongate body portion to be moved along a path, one or more datums, and a plurality of sense elements disposed at positions spaced along a length of the elongate body portion. Each sense element may sense or be sensed by one of the datums when in proximity to the datum. The system may also include a processor configured to compare signals transmitted from the datums or from the sense elements, including a first signal and a second signal, and identify, based on the comparison, a state of motion of the elongate body chosen from a state of motion in a forward direction (insertion) along a path and a state of motion in a rearward direction (withdrawal) along the path. The processor may identify the state of motion of the elongate body based on whether the first signal is lower than or higher than the second signal and whether the first and second signals are both increasing or decreasing.