Abstract: A method and apparatus for reducing magnetic tracking error in the position and orientation determined in a magnetic tracking system having a magnetic field generator. In some embodiments, the measured position and orientation of a sensor is compared to an expected theoretical position and orientation. Any error is assumed to be from “floor distortion,” i.e., eddy currents in the floor caused by the magnetic field generated by the magnetic field transmitter. The floor distortion is modeled as being caused by eddy currents caused by a second magnetic field transmitter that is a reflection of the actual transmitter. An algorithm iteratively searches over a parameter space to minimize the difference between the measured position and orientation and the theoretical position and orientation, and applies a correction to the measured position and orientation. The measurements and corrections of the position and orientation run in real-time with no additional hardware or calibration required.

Abstract: A system and method that can automatically select a frequency of a magnetic field in a magnetic tracking system. A magnetic tracking system emits an alternating magnetic field using a set of three frequencies. In the present approach, a transmitter is capable of generating multiple sets of three frequencies. A processor selects a first set of frequencies to use and causes the receiver to measure the amplitude of the magnetic field at those frequencies. In one embodiment, the frequency set having the lowest energy is selected. The processor then compares an estimated jitter at those frequencies to the actual jitter experienced using the frequencies. If the actual jitter exceeds the estimated jitter by a predetermined amount, the processor switches to a different set of frequencies and causes the receiver to measure the magnetic field at the new set of frequencies. The process may repeat using the additional sets of frequencies.

Abstract: A system and method that can automatically select a frequency of a magnetic field in a magnetic tracking system. A magnetic tracking system emits an alternating magnetic field using a set of three frequencies. In the present approach, a transmitter is capable of generating multiple sets of three frequencies. A processor selects a first set of frequencies to use and causes the receiver to measure the amplitude of the magnetic field at those frequencies. In one embodiment, the frequency set having the lowest energy is selected. The processor then compares an estimated jitter at those frequencies to the actual jitter experienced using the frequencies. If the actual jitter exceeds the estimated jitter by a predetermined amount, the processor switches to a different set of frequencies and causes the receiver to measure the magnetic field at the new set of frequencies. The process may repeat using the additional sets of frequencies.

Abstract: A system and method that can automatically select a frequency of a magnetic field in a magnetic tracking system. A magnetic tracking system emits an alternating magnetic field using a set of three frequencies. In the present approach, a transmitter is capable of generating multiple sets of three frequencies. A processor selects a first set of frequencies to use and causes the receiver to measure the amplitude of the magnetic field at those frequencies. In one embodiment, the frequency set having the lowest energy is selected. The processor then compares an estimated jitter at those frequencies to the actual jitter experienced using the frequencies. If the actual jitter exceeds the estimated jitter by a predetermined amount, the processor switches to a different set of frequencies and causes the receiver to measure the magnetic field at the new set of frequencies. The process may repeat using the additional sets of frequencies.

Abstract: A system and method that can automatically select a frequency of a magnetic field in a magnetic tracking system. A magnetic tracking system emits an alternating magnetic field using a set of three frequencies. In the present approach, a transmitter is capable of generating multiple sets of three frequencies. A processor selects a first set of frequencies to use and causes the receiver to measure the amplitude of the magnetic field at those frequencies. In one embodiment, the frequency set having the lowest energy is selected. The processor then compares an estimated jitter at those frequencies to the actual jitter experienced using the frequencies. If the actual jitter exceeds the estimated jitter by a predetermined amount, the processor switches to a different set of frequencies and causes the receiver to measure the magnetic field at the new set of frequencies. The process may repeat using the additional sets of frequencies.

Abstract: A method and apparatus for reducing magnetic tracking error in the position and orientation determined in a magnetic tracking system having a magnetic field generator. In some embodiments, the measured position and orientation of a sensor is compared to an expected theoretical position and orientation. Any error is assumed to be from “floor distortion,” i.e., eddy currents in the floor caused by the magnetic field generated by the magnetic field transmitter. The floor distortion is modeled as being caused by eddy currents caused by a second magnetic field transmitter that is a reflection of the actual transmitter. An algorithm iteratively searches over a parameter space to minimize the difference between the measured position and orientation and the theoretical position and orientation, and applies a correction to the measured position and orientation. The measurements and corrections of the position and orientation run in real-time with no additional hardware or calibration required.

Abstract: A method and apparatus for reducing magnetic tracking error in the position and orientation determined in an electromagnetic tracking system is disclosed. In some embodiments, a corrected position and orientation is blended with an uncorrected position and orientation based upon the calculated probability of each. To determine a corrected position and orientation, data from an IMU in the receiver is used to obtain a constraint on the orientation. In other embodiments, the amount of detected error due to electromagnetic distortion is measured. Any error is first assumed to be from “floor distortion,” and a correction is applied. If the error is still deemed too great, a constraint is again obtained from IMU data. Using this constraint, another correction for the distortion is made. The solution from this correction may be blended with a standard solution and the solution from the floor distortion to arrive at a final solution.

Abstract: A method and apparatus is disclosed for allowing a magnetic tracking system to detect, and operate in close proximity in the same physical environment with, additional magnetic tracking systems. The first user's magnetic tracking system that becomes active in the physical space becomes the master system, and assigns time slots for its own transmitting antennas to generate the magnetic field which is used to determine the position and orientation of the user's limbs relative to the user's head. The master system also determines when other magnetic tracking systems become active in the physical space and assigns to those systems identification codes and time slots for their transmitting antennas to generate a magnetic field so that the position and orientation of the user's hands relative to the user's head for each of those systems may be determined. By requiring each magnetic tracking system to operate in different time slots, there is no interference between the systems.

Abstract: A system and method for performing synchronization of a magnetic field transmitter and receiver to resolve received signal phase ambiguity based upon the phases of the magnetic fields. Three orthogonal field frequencies are selected. A Fourier transform extracts the sine and cosine of the received signal, which provides the received signal phases and results in a complex signal matrix (“Sigmat”). A search is made for a phase rotation of the frequencies to achieve convergence of the Sigmat at a point it is real-valued; the search may be limited by aligning the Sigmat such that the major element becomes real-valued and rotating the other two frequencies. The correct phase is the one in which the Sigmat has a positive determinant and minimizes any remaining imaginary portion. A transmitter and receiver may be calibrated to account for any analog phase shift. Distortion of the magnetic field may also be detected and corrected.

Abstract: A system and method for performing synchronization of a magnetic field transmitter and receiver to resolve received signal phase ambiguity based upon the phases of the magnetic fields. Three orthogonal field frequencies are selected. A Fourier transform extracts the sine and cosine of the received signal, which provides the received signal phases and results in a complex signal matrix (“Sigmat”). A search is made for a phase rotation of the frequencies to achieve convergence of the Sigmat at a point it is real-valued; the search may be limited by aligning the Sigmat such that the major element becomes real-valued and rotating the other two frequencies. The correct phase is the one in which the Sigmat has a positive determinant and minimizes any remaining imaginary portion. A transmitter and receiver may be calibrated to account for any analog phase shift. Distortion of the magnetic field may also be detected and corrected.

Abstract: A method and apparatus for reducing magnetic tracking error in the position and orientation determined in an electromagnetic tracking system is disclosed. In some embodiments, a corrected position and orientation is blended with an uncorrected position and orientation based upon the calculated probability of each. To determine a corrected position and orientation, data from an IMU in the receiver is used to obtain a constraint on the orientation. In other embodiments, the amount of detected error due to electromagnetic distortion is measured. Any error is first assumed to be from “floor distortion,” and a correction is applied. If the error is still deemed too great, a constraint is again obtained from IMU data. Using this constraint, another correction for the distortion is made. The solution from this correction may be blended with a standard solution and the solution from the floor distortion to arrive at a final solution.

Abstract: A method and apparatus for self-relative body tracking in virtual reality systems using magnetic tracking is disclosed, which allows more accurate tracking of a user's body relative to the user's field of vision. A head-mounted magnetic tracking (HMMT) system is used, in which other parts of a user's body are tracked relative to the HMD on the user's head, rather than relative to a base station. This results in less distortion of the magnetic field used for tracking and thus allows for more accurate determination of the position and orientation of a user's body parts relative to the user's field of vision, so that a more accurate avatar may be presented on the HMD to the user. This allows the avatar of the user's body part to be shown in a location that corresponds closely to its physical position. In an alternative embodiment, multiple portions of the user's body may be tracked.

Abstract: A method and apparatus for self-relative body tracking in virtual reality systems using magnetic tracking is disclosed, which allows more accurate tracking of a user's body relative to the user's field of vision. A head-mounted magnetic tracking (HMMT) system is used, in which other parts of a user's body are tracked relative to the HMD on the user's head, rather than relative to a base station. This results in less distortion of the magnetic field used for tracking and thus allows for more accurate determination of the position and orientation of a user's body parts relative to the user's field of vision, so that a more accurate avatar may be presented on the HMD to the user. This allows the avatar of the user's body part to be shown in a location that corresponds closely to its physical position. In an alternative embodiment, multiple portions of the user's body may be tracked.

Abstract: A method and apparatus for self-relative body tracking in virtual reality systems using magnetic tracking is disclosed, which allows more accurate tracking of a user's body relative to the user's field of vision. A head-mounted magnetic tracking (HMMT) system is used, in which other parts of a user's body are tracked relative to the HMD on the user's head, rather than relative to a base station. This results in less distortion of the magnetic field used for tracking and thus allows for more accurate determination of the position and orientation of a user's body parts relative to the user's field of vision, so that a more accurate avatar may be presented on the HMD to the user. This allows the avatar of the user's body part to be shown in a location that corresponds closely to its physical position. In an alternative embodiment, multiple portions of the user's body may be tracked.

Abstract: An electromagnetic tracking system with three non-concentric, non-parallel transmitter coils to generate the magnetic fields and sensor coils to generate magnetic sensor data, from which position and orientation of the sensor is determined. In one embodiment, the three non-concentric transmitter coils are attached to or mounted in a Head Mounted Display (HMD). Having the three transmitter coils be non-concentric reduces overall bulkiness and spreads the weight of the transmitter coils over a larger area.

Abstract: A method and apparatus is disclosed for allowing a magnetic tracking system to detect, and operate in close proximity in the same physical environment with, additional magnetic tracking systems. The first user's magnetic tracking system that becomes active in the physical space becomes the master system, and assigns time slots for its own transmitting antennas to generate the magnetic field which is used to determine the position and orientation of the user's limbs relative to the user's head. The master system also determines when other magnetic tracking systems become active in the physical space and assigns to those systems identification codes and time slots for their transmitting antennas to generate a magnetic field so that the position and orientation of the user's hands relative to the user's head for each of those systems may be determined. By requiring each magnetic tracking system to operate in different time slots, there is no interference between the systems.

Abstract: A method and apparatus for self-relative body tracking in virtual reality systems using magnetic tracking is disclosed, which allows more accurate tracking of a user's body relative to the user's field of vision. A head-mounted magnetic tracking (HMMT) system is used, in which other parts of a user's body are tracked relative to the HMD on the user's head, rather than relative to a base station. This results in less distortion of the magnetic field used for tracking and thus allows for more accurate determination of the position and orientation of a user's body parts relative to the user's field of vision, so that a more accurate avatar may be presented on the HMD to the user. This allows the avatar of the user's body part to be shown in a location that corresponds closely to its physical position. In an alternative embodiment, multiple portions of the user's body may be tracked.

Abstract: 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.

Abstract: A method and apparatus for self-relative body tracking in virtual reality systems using magnetic tracking is disclosed, which allows more accurate tracking of a user's body relative to the user's field of vision. A head-mounted magnetic tracking (HMMT) system is used, in which other parts of a user's body are tracked relative to the HMD on the user's head, rather than relative to a base station. This results in less distortion of the magnetic field used for tracking and thus allows for more accurate determination of the position and orientation of a user's body parts relative to the user's field of vision, so that a more accurate avatar may be presented on the HMD to the user. This allows the avatar of the user's body part to be shown in a location that corresponds closely to its physical position. In an alternative embodiment, multiple portions of the user's body may be tracked.

Abstract: 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.