Determining location using magnetic fields from AC power lines

Patent metadata

Field	Value
Publication number	US-9551561-B2
Application number	US-201414185346-A
Country	US
Kind code	B2
Filing date	Feb 20, 2014
Priority date	Dec 4, 2013
Publication date	Jan 24, 2017
Grant date	Jan 24, 2017

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.

First claim

What is claimed is:

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 determining one or more of the plurality of characteristics comprises isolating a component of the magnetic field that exhibits a frequency at which electrical power is transmitted along one or more power lines;
communicating, by the one or more computing devices, with a server over a network to obtain 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 stored by the server;
comparing, by the one or more computing devices, the plurality of characteristics to the plurality of expected values associated with each of the plurality of locations;
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 such location; and
determining, by the one or more computing devices, a device location based at least in part on the plurality of location probabilities respectively determined for the plurality of locations.

2. 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.

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:
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.

4. 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.

5. 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.

6. 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.

7. The method of claim 1 , wherein determining, by the one or more computing devices, the device location comprises determining, by the one or more computing devices, the device location in three-dimensional space.

8. The method of claim 1 , further comprising:
uploading, by the one or more computing devices to the server, one or more of the plurality of location probabilities associated with the plurality of locations and one or more of the plurality of characteristics for use in updating the map.

9. 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, wherein determining, for each of the plurality of readings, the plurality of characteristics comprises isolating the component of the magnetic field that oscillates at the frequency associated with the one or more alternating current power conductors;
communicating with a server over a network to obtain 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 stored by the server;
comparing, for each of the plurality of readings, the plurality of characteristics for such reading to the plurality of expected values associated with the plurali

Assignees

• Google Inc

Inventors

• Kochanski Gregory Peter

Classifications

• G01B7/004 Primary

  for measuring coordinates of points · CPC title

• G01S5/0205

  Details · CPC title