Errors in systems using magnetic fields to locate objects

A program storage medium storing computer executable instructions, the instructions to cause a computer to:

• receive data representative of measured magnetic field values that depend on a probe's location and orientation;
• determine one of the probe's location and the probe's orientation from an extremum of an optimization function, the function depending on differences between the measured field values and field values from a model, determine one of the probe's location and the probe's orientation includes:
• guess a location and orientation of the probe,
• calculate magnetic field values associated with the guessed location and orientation from a model, and
• evaluate a new value of the optimization function from the calculated and measured values;
• reject the guessed location and orientation in response to the new value being farther from an extremum of the function than an earlier calculated value of the function;
• indicate that a distortion to the determining exists in response to the extremum belonging to a preselected range associated with presence of distortion;
• and
• provide a predicted value for one of the probe's location and the probe's orientation in response to the extremum belonging to another preselected range of values.

A process for detecting distortions to probe location or orientation determinations, comprising:

• determining a preselected range of values associated with the presence of a certain condition;
• measuring a plurality of magnetic field values, the measured values depending on a probe's location and a probe's orientation;
• determining one of the probe's location and the probe's orientation from an extremum of an optimization function, the function depending on differences between the measured field values and field values from a model;
• and
• indicating that a distortion to the determining exists in response to the extremum belonging to the preselected range of values associated with presence of a certain condition;
• wherein determining a preselected range includes:
• setting up a condition that distorts determinations of the probe's location and the probe's orientation from measured fields,
• determining an actual probe location and orientation,
• measuring magnetic field values depending on the location and orientation,
• finding an extremum of an optimization function that depends on differences between the measured field values and field values calculated from a model and guessed probe location and position, and
• assigning the extremum to the preselected range of values associated with the presence of the certain condition.