6DOF Two State Electromagnetic Trackers

• Raab's two-state tracker uses two transmitter coils instead of the usual three transmitter coils, as discussed in the following paper:

• Frederick H. Raab, "Quasi-Static Magnetic-Field Technique for Determining Position and Orientation", IEEE Transactions on Geoscience and Remote Sensing, Vol. GE-19, No. 4, October 1981, pages 235-243. Section "Two-State_Excitation" has direct solution for cartesian-coordinates position first and then for orientation. The position solution can generate NANs.

• Eugene Paperno, Ichiro Sasada, and Eduard Leonovich, "A New Method for Magnetic Position and Orientation Tracking", IEEE Transactions on Magnetics, vol. 37, No.4, July 2001, has direct solution for spherical-coordinates position first and then for orientation. The position solution never generates NANs, but does clearly show the limitations of two-state: Positions on or close to the missing transmitter-coil axis, are inaccessible. Positions in the plane of the two present transmitter-coil axes, are very noisy.

• By electromagnetic reciprocity, one can use a three-axis transmitter with a two-axis receiver, as detailed in the following paper:

• Eugene Paperno and Pavel Keisar, "Three-Dimensional Magnetic Tracking of Biaxial Sensors", IEEE Transactions on Magnetics, vol. 40, No.3, May 2004, has good discussion with figures detailing the inaccuracy near receiver-coil axes.