Method and apparatus for correcting magnetic tracking error with inertial measurement
A method and apparatus is disclosed for synchronizing a magnetic field transmitter and receiver to resolve phase ambiguity so that phase information for the position and orientation of the receiver may be derived and maintained. A synchronization process allows for the phase information to be initially derived based upon known information from other sources, and then tracked from one measurement to the next. In another embodiment, information from an inertial measurement unit (IMU) is used to determine the phase information or to correct for errors in the determination from receiver data of the position and orientation of a receiver, and prevent such errors from accumulating as the receiver moves away from a transmitter.
1. A method of using an inertial measurement unit (IMU) to correct for error in a measured position vector and orientation of a tracking device containing a receiver in a magnetic tracking system having a transmitter and displaying the tracking device corresponding to an actual position and corrected orientation of the receiver, comprising:
displaying on a display the tracking device based on a measured position and orientation of the receiver relative to the transmitter;
receiving at a processor a gravity vector and position vector as measured by the receiver;
determining by the processor a true gravity vector from information from the IMU;
computing by the processor an angle of geodesic rotation between a gravity vector as measured by the receiver and the true gravity vector as a rotation error quaternion;
performing by the processor a spherical interpolation to reduce the angle of geodesic rotation by half to form a position correction quaternion;
rotating by the processor the measured position vector about an origin of the tracking space using the position correction quaternion to produce a corrected position vector indicating the actual position of the receiver relative to the transmitter; and
determining by the processor a corrected orientation of the receiver relative to the transmitter based upon the rotation error quaternion and the measured orientation; and
displaying on the display the tracking device in the actual position and corrected orientation of the receiver relative to the transmitter.
2. A non-transitory computer readable storage medium having embodied thereon instructions for causing a computing device to execute a method of using an inertial measurement unit (IMU) to correct for error in a measured position vector and orientation of a tracking device containing a receiver in a magnetic tracking system having a transmitter and displaying the tracking device corresponding to an actual position and corrected orientation of the receiver, the method comprising:
generating instructions to display on a display device the tracking device based on a measured position and orientation of the receiver relative to the transmitter;
receiving a gravity vector and position vector as measured by the receiver;
determining a true gravity vector from information from the IMU;
computing an angle of geodesic rotation between a gravity vector as measured by the receiver and the true gravity vector as a rotation error quaternion;
performing a spherical interpolation to reduce the angle of geodesic rotation by half to form a position correction quaternion;
rotating the measured position vector about an origin of the tracking space using the position correction quaternion to produce a corrected position vector indicating the actual position of the receiver relative to the transmitter;
determining a corrected orientation of the receiver relative to the transmitter based upon the rotation error quaternion and the measured orientation; and
generating instructions to display on a display device the tracking device in the actual position and corrected orientation of the receiver relative to the transmitter.
3. A system for using an inertial measurement unit (IMU) to correct for error in a measured position vector and orientation of a tracking device containing a receiver in a magnetic tracking system having a transmitter and displaying the tracking device corresponding to an actual position and corrected orientation of the receiver, comprising:
a transmitter comprising a plurality of source magnetic coils each configured to generate a magnetic field;
a tracking device comprising an inertial measurement unit (IMU) and a receiver, the receiver comprising a plurality of sensor magnetic coils configured to sense the magnetic fields and to generate a signal matrix representing the position and orientation of the receiver relative to the transmitter;
a processor configured to:
provide instructions to a display device to display the tracking device based on a measured position and orientation of the receiver relative to the transmitter;
receive a gravity vector and position vector as measured by the receiver;
determine a true gravity vector from information from the IMU;
compute an angle of geodesic rotation between a gravity vector as measured by the receiver and the true gravity vector as a rotation error quaternion;
perform a spherical interpolation to reduce the angle of geodesic rotation by half to form a position correction quaternion;
rotate the measured position vector about an origin of the tracking space using the position correction quaternion to produce a corrected position vector indicating the actual position of the receiver relative to the transmitter;
determine a corrected orientation of the receiver relative to the transmitter based upon the rotation error quaternion and the measured orientation; and
provide instructions to the display device to display the tracking device in the actual position and corrected orientation of the receiver relative to the transmitter.
4. The method of claim 1 wherein rotating by the processer the measured position vector about an origin of the tracking space using the position correction quaternion is determined by a suitable curve fitting function.
5. The non-transitory computer readable storage medium of claim 2 wherein rotating the measured position vector about an origin of the tracking space using the position correction quaternion is determined by a suitable curve fitting function.
6. The system of claim 3 wherein the processor configured to rotate the measured position vector about an origin of the tracking space using the position correction quaternion is configured to be determined by a suitable curve fitting function.