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 the missing receiver coil and near the plane of the two present receiver coils.