Electromagnetic tracking: Difference between revisions
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[[Electromagnetic tracking]] ('''EMT''') is a [[Pose]]-estimation technology widely used in [[virtual reality]] (VR), [[augmented reality]] (AR), medical navigation, and human–[[robotics|robot–computer interaction]]. | |||
Unlike camera-based | Unlike camera-based [[optical tracking]] or pure [[inertial tracking]], EMT determines the ''six-degree-of-freedom'' ([[6DOF]]) position and orientation of miniature sensor coils without requiring line-of-sight. A stationary [[field generator]] produces a precisely controlled magnetic field. Tri-axial receiver coils measure that field, and the system solves for each sensor’s pose every frame. Because each frame is computed independently, EMT suffers **no cumulative drift**, while latencies are typically only a few milliseconds.<ref>Yaniv Z., Wilson E., Lindisch D., Cleary K. “Electromagnetic tracking in the clinical environment.” ''Medical Physics'' 36 (3): 876-892 (2009). doi:10.1118/1.3075829.</ref> | ||
==History== | ==History== | ||
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==Technical characteristics== | ==Technical characteristics== | ||
===Field Generators=== | |||
Transmitters are supplied as planar plates, cube frames, or towers. A standard Polhemus FASTRAK source covers ≈1.5 m × 1.5 m × 1.5 m at up to 120 Hz.<ref>Polhemus. “Motion Tracking Technical Comparison Chart.” PDF, 2020.</ref> | Transmitters are supplied as planar plates, cube frames, or towers. A standard Polhemus FASTRAK source covers ≈1.5 m × 1.5 m × 1.5 m at up to 120 Hz.<ref>Polhemus. “Motion Tracking Technical Comparison Chart.” PDF, 2020.</ref> | ||
===Sensors=== | |||
Modern sensors are extremely small: the Aurora 6DOF “micro” sensor is only 1.8 mm Ø, while its smallest 5DOF sensor is 0.3 mm Ø.<ref>Northern Digital Inc. “Aurora Electromagnetic Tracking – Sensors & Tools.” NDigital.com, accessed 30 April 2025.</ref> A single Aurora controller can track up to 32 5DOF or 16 6DOF sensors. | Modern sensors are extremely small: the Aurora 6DOF “micro” sensor is only 1.8 mm Ø, while its smallest 5DOF sensor is 0.3 mm Ø.<ref>Northern Digital Inc. “Aurora Electromagnetic Tracking – Sensors & Tools.” NDigital.com, accessed 30 April 2025.</ref> A single Aurora controller can track up to 32 5DOF or 16 6DOF sensors. | ||
===Performance=== | |||
Static laboratory accuracy for FASTRAK is ≈0.76 mm RMS and 0.15° RMS<ref>Polhemus. “Motion Tracking Technical Comparison Chart.”</ref>; update rates range 50–120 Hz; latency is 3–10 ms. Real-world performance degrades near conductive or ferromagnetic objects, high-current devices, or at distances >1 m, where the field drops rapidly. | Static laboratory accuracy for FASTRAK is ≈0.76 mm RMS and 0.15° RMS<ref>Polhemus. “Motion Tracking Technical Comparison Chart.”</ref>; update rates range 50–120 Hz; latency is 3–10 ms. Real-world performance degrades near conductive or ferromagnetic objects, high-current devices, or at distances >1 m, where the field drops rapidly. | ||
===AC vs. Pulsed-DC=== | |||
AC trackers (Polhemus, NDI) supply strong continuous fields but are susceptible to eddy-current distortion. Pulsed-DC trackers (Ascension “Bird”) reduce such distortion at the cost of lower refresh rates.<ref>Ascension Technology Corp. “Pulsed DC Magnetic Tracking Technology Overview.”</ref> | AC trackers (Polhemus, NDI) supply strong continuous fields but are susceptible to eddy-current distortion. Pulsed-DC trackers (Ascension “Bird”) reduce such distortion at the cost of lower refresh rates.<ref>Ascension Technology Corp. “Pulsed DC Magnetic Tracking Technology Overview.”</ref> | ||
==Comparison with | ==Comparison with Other Tracking Modalities== | ||
{| class="wikitable" | {| class="wikitable" | ||
! Modality !! Key strengths !! Key limitations | ! Modality !! Key strengths !! Key limitations | ||