Electromagnetic tracking: Difference between revisions - VR & AR Wiki

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==History==

Commercial EMT began with [[Polhemus]]’s 1969 [[Space-Tracker]], followed by its FASTRAK line in the 1980s and [[Ascension Technology|Ascension]]’s pulsed-DC ‘‘Flock of Birds’’ (1991).<ref name="FASTRAK2018">Polhemus. “FASTRAK® Motion Tracking System — Product Overview.” PDF brochure, 2018. Accessed 30 Apr 2025.</ref><ref name="Flock2002">Ascension Technology Corp. ''Flock of Birds® Installation and Operation Guide,'' Rev B (2002).</ref>

Commercial EMT began with [[Polhemus]]’s 1969 [[Space-Tracker]], followed by its FASTRAK line in the 1980s and [[Ascension Technology|Ascension]]’s pulsed-DC ‘‘Flock of Birds’’ (1991).<ref name="FASTRAK2018">Polhemus. “FASTRAK® Motion Tracking System - Product Overview.” PDF brochure, 2018. Accessed 30 Apr 2025.</ref><ref name="Flock2002">Ascension Technology Corp. ''Flock of Birds® Installation and Operation Guide,'' Rev B (2002).</ref>

During the 1990s EMT migrated from military simulators into VR CAVEs and into medical navigation. Key medical trackers such as [[NDI Aurora]] (2002) made EMT the de-facto standard for surgical tool tracking. Consumer products followed: the [[Razer Hydra]] PC controller (2011) and the “Control” wand for the original [[Magic Leap One]] AR headset (2018) both employ EMT.<ref name="Hayden2018">Hayden S. “Magic Leap One Controller Appears in FCC Filing, Release on Track for 2018.” ''Road to VR,'' 21 Jun 2018.</ref><ref name="Razer2011">Razer Inc. “Thanks to the Razer Hydra, Now You’re Thinking With Motion Control.” Press release, 21 Apr 2011.</ref>

==Principles of operation==

A field generator contains three orthogonal transmitter coils driven sequentially (AC systems) or in short pulses (pulsed-DC systems). Each receiver holds three orthogonal pick-up coils. As every axis is energized, the induced voltages encode the local magnetic-field vector; an over-determined least-squares solve yields 3-D position and orientation.<ref name="pciBIRD">Ascension Technology Corp. “pciBIRD — Pulsed DC Magnetic Tracking.” Product sheet, accessed 30 Apr 2025.</ref>

A field generator contains three orthogonal transmitter coils driven sequentially (AC systems) or in short pulses (pulsed-DC systems). Each receiver holds three orthogonal pick-up coils. As every axis is energized, the induced voltages encode the local magnetic-field vector; an over-determined least-squares solve yields 3-D position and orientation.<ref name="pciBIRD">Ascension Technology Corp. “pciBIRD - Pulsed DC Magnetic Tracking.” Product sheet, accessed 30 Apr 2025.</ref>

For an ideal magnetic dipole the far-field magnitude decays with the inverse cube of distance (|B| ∝ 1/''r''³), sharply limiting working volume.<ref name="Jackson1998">Jackson J. D. ''Classical Electrodynamics,'' 3rd ed. Wiley (1998) p. 181.</ref>

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===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 name="AuroraTools">Northern Digital Inc. “Aurora Electromagnetic Tracking — Sensors & Tools.” Product page, accessed 30 Apr 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 name="AuroraTools">Northern Digital Inc. “Aurora Electromagnetic Tracking - Sensors & Tools.” Product page, accessed 30 Apr 2025.</ref> A single Aurora controller can track up to 32 5DOF or 16 6DOF sensors.

===Performance===