Systems and methods for extending the spatial coverage of a reference pressure network

1. A method comprising:

determining that an estimated position of a mobile device resides outside a coverage area of a network of reference pressure sensors;

for each reference pressure sensor from the network of reference pressure sensors, determine a reference-level pressure for a reference-level altitude using a measurement of pressure from that reference pressure sensor and an altitude of that reference pressure sensor;

using a first set of reference-level pressures that were not determined using the network of reference pressure sensors to determine a pressure pattern for a region that includes the estimated position and an area not included in the coverage area of the network of reference pressure sensors, the pressure pattern including a set of isobars;

using the reference-level pressures determined for the reference pressure sensors of the network of reference pressure sensors and the pressure pattern determined for the region to determine a reference-level pressure value for use in calibrating a pressure sensor of the mobile device or for use in estimating an altitude of the mobile device; and

calibrating the pressure sensor of the mobile device or estimating the altitude of the mobile device using the determined reference-level pressure value;

wherein determining the reference-level pressure value for use in calibrating the pressure sensor of the mobile device or for use in estimating an altitude of the mobile device comprises:

selecting a first isobar from the set of isobars that passes through the coverage area of the network of reference pressure sensors and that is the closest isobar to the estimated position of the mobile device;

at each location of a plurality of different locations on the first isobar inside the coverage area of the network of reference pressure sensors, determining an estimated reference-level pressure at that location on the first isobar using reference-level pressures that are generated based on one or more of the reference-level pressures determined for the reference pressure sensors from the network of reference pressure sensors;

identifying a first maximum estimated reference-level pressure and a first minimum estimated reference-level pressure from the estimated reference-level pressures;

determining if the first maximum estimated reference-level pressure and the first minimum estimated reference-level pressure are within a predefined amount of pressure; and

if the first maximum estimated reference-level pressure and the first minimum estimated reference-level pressure are within the predefined amount of pressure, determining a first mean reference-level pressure value using the estimated reference-level pressures that are at the plurality of different locations on the first isobar, and using the first mean reference-level pressure value as the reference-level pressure value for use in calibrating the pressure sensor of the mobile device or for use in estimating the altitude of the mobile device.

2. The method of claim 1 , wherein if the first maximum estimated reference-level pressure and the first minimum estimated reference-level pressure are not within the predefined amount of pressure:

selecting a second isobar from the set of isobars that passes through the coverage area of the network of reference pressure sensors and that is the second closest isobar to the estimated position of the mobile device;

at each location of a plurality of different locations on the second isobar inside the coverage area of the network of reference pressure sensors, determining an estimated reference-level pressure at that location on the second isobar using reference-level pressures that are generated based on one or more of the reference-level pressures determined for the reference pressure sensors from the network of reference pressure sensors;

identifying a second maximum estimated reference-level pressure and a second minimum estimated reference-level pressure from the estimated reference-level pressures;

determining if the second maximum estimated reference-level pressure and the second minimum estimated reference-level pressure are within the predefined amount of pressure; and

if the second maximum estimated reference-level pressure and the second minimum estimated reference-level pressure are within the predefined amount of pressure, determining a second mean reference-level pressure value using the estimated reference-level pressures that are at the plurality of different locations on the second isobar, and using the second mean reference-level pressure value as the reference-level pressure value for use in calibrating the pressure sensor of the mobile device or for use in estimating the altitude of the mobile device.

3. The method of claim 1 , wherein if the first maximum estimated reference-level pressure and the first minimum estimated reference-level pressure are not within the predefined amount of pressure:

determining if an amount of pressure separating the first isobar and a second isobar from the set of isobars that passes through the coverage area of the network of reference pressure sensors and that is the second closest isobar to the estimated position of the mobile device exceeds a tolerated pressure error; and

only if the amount of pressure separating the first isobar and the second isobar does not exceed the tolerated pressure error:

(a) at each location of a plurality of different locations on the second isobar inside the coverage area of the network of reference pressure sensors, determining an estimated reference-level pressure at that location on the second isobar using reference-level pressures that are generated based on one or more of the reference-level pressures determined for the reference pressure sensors from the network of reference pressure sensors;

(b) identifying a second maximum estimated reference-level pressure and a second minimum estimated reference-level pressure from the estimated reference-level pressures;

(c) determining if the second maximum estimated reference-level pressure and the second minimum estimated reference-level pressure are within the predefined amount of pressure; and

(d) if the second maximum estimated reference-level pressure and the second minimum estimated reference-level pressure are within the predefined amount of pressure, determining a second mean pressure value using the estimated reference-level pressures that are at the plurality of different locations on the second isobar, and using the second mean reference-level pressure value as the reference-level pressure value for use in calibrating the pressure sensor of the mobile device or for use in estimating the altitude of the mobile device.

4. The method of claim 1 , wherein if the first maximum estimated reference-level pressure and the first minimum estimated reference-level pressure are not within the predefined amount of pressure:

determining an amount of pressure separating the first isobar and a second isobar from the set of isobars that passes through the coverage area of the network of reference pressure sensors and that is the second closest isobar to the estimated position of the mobile device;

determining if the amount of pressure is less than or equal to one-half of a tolerated pressure error; and

only if the amount of pressure is less than or equal to one-half of the tolerated pressure error:

(a) at each location of a plurality of different locations on the second isobar inside the coverage area of the network of reference pressure sensors, determining an estimated reference-level pressure at that location on the second isobar using reference-level pressures that are generated based on one or more of the reference-level pressures determined for the reference pressure sensors from the network of reference pressure sensors;

(b) identifying a second maximum estimated reference-level pressure and a second minimum estimated reference-level pressure from the estimated reference-level pressures;

(c) determining if the second maximum estimated reference-level pressure and the second minimum estimated reference-level pressure are within the predefined amount of pressure; and

(d) if the second maximum estimated reference-level pressure and the second minimum estimated reference-level pressure are within the predefined amount of pressure, determining a second mean pressure value using the estimated reference-level pressures that are at the plurality of different locations on the second isobar, and using the second mean reference-level pressure value as the reference-level pressure value for use in calibrating the pressure sensor of the mobile device or for use in estimating the altitude of the mobile device.

5. The method of claim 1 , wherein if the first maximum estimated reference-level pressure and the first minimum estimated reference-level pressure are not within the predefined amount of pressure:

determining if a second isobar from the set of isobars passes through the coverage area of the network of reference pressure sensors; and

only if the second isobar from the set of isobars passes through the coverage area of the network of reference pressure sensors:

(a) at each location of a plurality of different locations on the second isobar inside the coverage area of the network of reference pressure sensors, determining an estimated reference-level pressure at that location on the second isobar using reference-level pressures that are generated based on one or more of the reference-level pressures determined for the reference pressure sensors from the network of reference pressure sensors;

(b) identifying a second maximum estimated reference-level pressure and a second minimum estimated reference-level pressure from the estimated reference-level pressures;

(c) determining if the second maximum estimated reference-level pressure and the second minimum estimated reference-level pressure are within the predefined amount of pressure; and

(d) if the second maximum estimated reference-level pressure and the second minimum estimated reference-level pressure are within the predefined amount of pressure, determining a second mean pressure value using the estimated reference-level pressures that are at the plurality of different locations on the second isobar, and using the second mean reference-level pressure value as the reference-level pressure value for use in calibrating the pressure sensor of the mobile device or for use in estimating the altitude of the mobile device.

6. One or more non-transitory machine-readable media embodying program instructions that, when executed by one or more machines, cause the one or more machines to implement the method of claim 1 .

7. A system comprising: a memory comprising computer-executable instructions; and a machine configured to execute the computer-executable instructions and cause the processing system to perform the method of claim 1 .