Methods and apparatus for electromagnetic position and orientation tracking with distortion compensation

A method of determining the position and orientation of an object within a bounded volume in the presence of electromagnetic distortion, comprising the steps of:

• a) generating an electromagnetic field having magnetic induction-vector components from a stationary source;
• b) measuring the components of the electromagnetic field at one or more stationary points near or within the volume;
• c) measuring the components of the electromagnetic field at one or more points relative to the object;
• d) computing the characteristics of an effective electromagnetic field, which would be produced by the stationary source in the vicinity of a given witness sensor along with electromagnetic distortion present in the bounded volume;
• e) receiving the induction-vector components measured relative to the object;
• and
• f) computing the position and orientation of the object by applying the characteristics of the effective field to the induction-vector components.

In a position/orientation tracking system of the type wherein AC electromagnetic radiation is received by a probe sensor disposed on an object being tracked in the presence of electromagnetic distortion, the improvement comprising:

• at least one witness sensor having a known fixed position and orientation within the field relative to the source of the electromagnetic distortion;
• and
• processor means in communication with the witness sensor for:
• a) computing a non-distorted model field proximate to the witness sensor, and
• b) computing the position and orientation of the object with probe sensor attached to the object as if the object were located within the non-distorted model field.