Distortion correction of magnetic fields for position tracking

Electro-magnetic tracking systems are in wide-spread use for measuring 6D positions. However, their accuracy is impaired seriously by distortions of the magnetic fields caused by many types of metal which are omnipresent at real sites. We present a fast and robust method for "equalizing" those distortions in order to yield accurate tracking. The algorithm is based on global scattered data interpolation using a "snap-shot" of the magnetic field's distortion measured once in advance. The algorithm is fast (it does not introduce any further lag in the data flow), robust, the samples of the field's "snap-shot" can be arranged in any way, and it is easy to implement. The distortion is visualized in an intuitive way to provide insight into its nature, and the correction algorithm is evaluated in terms of accuracy and performance. Finally, a qualitative comparison of the susceptibility of a Polhemus and an Ascension tracking system is carried out.