Determining Location Using Magnetic Fields From AC Power Lines

• US 20150153151A1
• Filed: 02/20/2014
• Published: 06/04/2015
• Est. Priority Date: 12/04/2013
• Status: Active Grant

• Current Assignee: Google LLC (Alphabet Inc.)
• Original Assignee: Google Inc. (Alphabet Inc.)
• Inventors: Kochanski, Gregory Peter
• Granted Patent: US 9,551,561 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G01B 7/004 for measuring coordinates of points

Abstract

Systems and methods for determining location using magnetic fields from AC power lines are provided. As an example, each magnetic field reading collected by the device over time can be analyzed to determine a plurality of characteristics of the magnetic field. One or more of the plurality of characteristics can describe a component of the magnetic field that oscillates at a frequency associated with the AC power lines. The plurality of characteristics can be compared to expected values respectively associated with a plurality of locations and provided by a map of the magnetic field to determine a location at which each magnetic field reading was collected. In further embodiments, magnetic field readings collected by the device over time can be analyzed in conjunction with other data or constraints to determine a trajectory of the device. In addition, the map can be updated using the collected readings and the determined trajectory.

Claims

1. A method for determining location using magnetic field readings, the method comprising:

obtaining, by one or more computing devices, a reading of a magnetic field collected by a magnetometer;

determining, by the one or more computing devices, a plurality of characteristics of a magnetic field based at least in part on the reading, wherein one or more of the plurality of characteristics describe a component of the magnetic field that exhibits a frequency at which electrical power is transmitted along one or more power lines;

comparing, by the one or more computing devices, the plurality of characteristics to a plurality of expected values associated with each of a plurality of locations, wherein the plurality of expected values for each location are provided by a map of the magnetic field.

2. The method of claim 1, further comprising determining, by the one or more computing devices, a location probability for each of the plurality of locations based at least in part on the respective comparison of the plurality of characteristics to the plurality of expected values associated with each of the plurality of locations.

3. The method of claim 1, wherein:

the reading of the magnetic field comprises a recording of data output by the magnetometer, wherein the data describes the magnetic field in three dimensions;

the plurality of characteristics comprise an x-axis amplitude, a y-axis amplitude, a z-axis amplitude, an x-axis phase value, a y-axis phase value, and a z-axis phase value of the component of the magnetic field that exhibits the frequency at which electrical power is transmitted along the one or more power lines; and

determining, by the one or more computing devices, the plurality of characteristics of the magnetic field based at least in part on the reading comprises;

fitting, by the one or more computing devices, a model waveform to each dimension of the recording to obtain a fitted recording, wherein the model waveform comprises a sine wave of the frequency at which electrical power is transmitted along the one or more power lines; and

determining, by the one or more computing devices, the plurality of characteristics of the magnetic field based at least in part on the fitted recordings.

4. The method of claim 1, wherein:

the reading of the magnetic field comprises a recording of data output by the magnetometer, wherein the data describes the magnetic field in three dimensions;

the plurality of characteristics comprise an x-axis amplitude, a y-axis amplitude, a z-axis amplitude, an x-axis phase value, a y-axis phase value, and a z-axis phase value of the component of the magnetic field that exhibits the frequency at which electrical power is transmitted along the one or more power lines; and

determining, by the one or more computing devices, the plurality of characteristics of the magnetic field based at least in part on the reading comprises;

applying, by the one or more computing devices, a digital filter to the recording to isolate the component of the magnetic field that exhibits the frequency at which electrical power is transmitted along the one or more power lines; and

determining, by the one or more computing devices, the plurality of characteristics of the magnetic field based at least in part on the filtered recording.

5. The method of claim 1, wherein determining, by the one or more computing devices, the plurality of characteristics of the magnetic field based at least in part on the reading comprises:

determining, by the one or more computing devices, an orientation of the magnetometer;

rotating, by the one or more computing devices, the reading of the magnetic field from a device coordinate frame to a global coordinate frame based at least in part on the orientation; and

determining, by the one or more computing devices, the plurality of characteristics of the magnetic field based at least in part on the rotated reading.

6. The method of claim 1, wherein:

the plurality of characteristics of the magnetic field comprise the dot product of an in-phase vector with a DC vector, the dot product of an out-of-phase vector with the DC vector; and

the dot product of the in-phase vector with the out-of-phase vector;

the DC vector describes a component of the magnetic field that exhibits a frequency at about zero;

the in-phase vector comprises the cosine of a phase angle value times an AC vector describing the component of the magnetic field that exhibits a frequency at which electrical power is transmitted along one or more power lines; and

the out-of-phase vector comprises the sine of the phase angle value times the AC vector.

7. The method of claim 1, wherein:

the plurality of characteristics of the magnetic field comprise a vertical portion of each of a DC vector, an in-phase vector, and an out-of-phase vector, the dot product of a horizontal plane portion of the in-phase vector with a horizontal plane portion of the DC vector, the dot product of a horizontal plane portion of the out-of-phase vector with the horizontal plane portion of the DC vector, and the dot product of the horizontal plane portion of the in-phase vector with the horizontal plane portion of the out-of-phase vector;

the DC vector describes a component of the magnetic field that exhibits a frequency at about zero;

the in-phase vector comprises a time average of the cosine of a phase angle value times an AC vector describing the component of the magnetic field that exhibits a frequency at which electrical power is transmitted along one or more power lines; and

the out-of-phase vector comprises a time average of the sine of the phase angle value times the AC vector.

8. One or more non-transitory computer-readable media storing instructions that, when executed by one or more computing devices, cause the one or more computing devices to perform operations, the operations comprising:

obtaining a plurality of readings of a magnetic field respectively associated with a plurality of times;

determining, for each of the plurality of readings, a plurality of characteristics of a component of the magnetic field that oscillates at a frequency associated with one or more alternating current power conductors;

respectively determining, for each of the plurality of times, a plurality of location probabilities for a plurality of locations based at least in part on the plurality of characteristics of the component of the magnetic field that oscillates at the frequency associated with one or more alternating current power conductors determined for the reading associated with such time;

determining a trajectory based at least in part on the plurality of location probabilities associated with each of the plurality of times.

9. The one or more non-transitory computer-readable media of claim 8, wherein determining, for each of the plurality of readings, the plurality of characteristics of the component of the magnetic field that oscillates at the frequency associated with one or more alternating current power conductors comprises determining, for each of the plurality of readings, an x-axis amplitude, a y-axis amplitude, a z-axis amplitude, an x-axis phase value, a y-axis phase value, and a z-axis phase value of the component of the magnetic field that oscillates at the frequency associated with one or more alternating current power conductors.

10. The one or more non-transitory computer-readable media of claim 8, wherein respectively determining, for each of the plurality of times, the plurality of location probabilities for the plurality of locations based at least in part on the plurality of characteristics associated with such time comprises respectively comparing, for each of the plurality of times, the plurality of characteristics with a plurality of expected values associated with each of the plurality of locations to respectively obtain the location probability for each location, wherein the plurality of expected values for each of the plurality of locations are obtained from a map of the magnetic field.

11. The one or more non-transitory computer-readable media of claim 8, wherein determining a trajectory based at least in part on the plurality of location probabilities associated with each of the plurality of times comprises determining a trajectory probability for each of a plurality of candidate trajectories based at least in part on the plurality of location probabilities associated with each of the plurality of times, wherein each of the plurality of candidate trajectories specifies one of the plurality of locations for each of the plurality of times, and wherein the trajectory probability for each of the plurality of candidate trajectories is based at least in part on the respective location probabilities associated with each of the plurality of locations specified by the candidate trajectory at the time specified by the candidate trajectory.

12. A system for determining locations using magnetic field readings, the system comprising:

one or more computing devices; and

one or more non-transitory computer-readable media storing instructions that, when executed by the one or more computing devices, cause the one or more computing devices to perform operations, the operations comprising;

obtaining a plurality of magnetic field readings respectively associated with a plurality of times;

determining a location probability for each of a plurality of locations for each of the plurality of times, wherein the location probability for each location for each time indicates the probability that the magnetic field reading collected at such time was collected at such location based at least in part on a comparison of the magnetic field reading to an expected reading associated with such location and such time; and

determining a trajectory probability for each of a plurality of trajectories, wherein each of the plurality of trajectories comprises a sequence of selected of the locations over the plurality of times.

13. The system of claim 12, wherein each of the plurality of magnetic field readings comprises an x-axis amplitude, a y-axis amplitude, a z-axis amplitude, an x-axis phase value, a y-axis phase value, and a z-axis phase value of a component of the magnetic field that oscillates at a frequency associated with one or more power lines, and wherein each of the plurality of expected readings comprises an expected x-axis amplitude, an expected y-axis amplitude, an expected z-axis amplitude, an expected x-axis phase value, an expected y-axis phase value, and an expected z-axis phase value of the component of the magnetic field that oscillates at the frequency associated with the one or more power lines.

14. The system of claim 12, wherein the one or more non-transitory computer-readable media store further instructions that, when executed by the one or more computing device, cause the one or more computing devices to perform operations, the operations comprising:

determining, for each of the plurality of times based at least in part on the magnetic field reading associated with such time, an AC vector describing a component of the magnetic field that oscillates at a frequency associated with one or more power lines;

multiplying the AC vector associated with each time by the cosine of an expected phase angle value associated with such time to obtain an in-phase vector; and

multiplying the AC vector associated with each time by the sine of an expected phase angle value associated with such time to obtain an out-of-phase vector;

wherein determining the location probability for each of the plurality of locations for each of the plurality of times comprises determining the location probability for each of the plurality of locations for each of the plurality of times based at least in part on the in-phase vector associated with such time and the out-of-phase vector associated with such time.

15. The system of claim 12, wherein:

the trajectory probability for each of the plurality of trajectories is determined based at least in part on the product of the location probability for each location included in the sequence of locations associated with such trajectory at the time specified by such sequence respectively multiplied by a transition probability for each location in the sequence of locations; and

the transition probability for each location in each sequence of locations provides a probability that a device has relocated from such location to the next location in such sequence of locations based at least in part on one or more constraints.

16. The system of claim 14, wherein the one or more constraints comprise one or more of data generated by one or more accelerometers and a threshold speed limitation.

17. The system of claim 12, wherein each of the plurality of trajectories further comprises a plurality of orientations respectively associated with the sequence of the locations associated with such trajectory.

18. The system of claim 12, wherein:

each expected reading is obtained from a map of the magnetic field; and

the one or more non-transitory computer-readable media store further instructions that, when executed by the one or more computing devices, cause the one or more computing devices to perform further operations, the further operations comprising updating the map based at least in part on one or more of the plurality of trajectory probabilities associated with the plurality of trajectories.

19. The system of claim 18, wherein updating the map based at least in part on one or more of the plurality of trajectory probabilities associated with the plurality of trajectories comprises respectively averaging, for one or more of the plurality of trajectories, the plurality of magnetic field readings with the plurality of expected readings associated with the sequence of locations associated with such trajectory.

20. The system of claim 18, wherein updating the map based at least in part on one or more of the plurality of trajectory probabilities associated with the plurality of trajectories comprises, for one or more of the plurality of trajectories, updating the expected values respectively associated with a plurality of neighboring locations of each location specified by the one or more of the plurality of trajectories based at least in part on the magnetic field reading associated with such location by the one or more of the plurality of trajectories.