Systems and methods for determining where to place atmospheric sensors used to estimate an altitude of a mobile device in an environment

1. A method for determining where to place atmospheric sensors that provide measurements of pressure used to estimate an altitude of a mobile device in an environment, the method comprising:

determining a reference-level pressure for each point in a grid of uniformly-distributed points in an environment, wherein each pair of adjacent points in the grid are separated by a predefined distance;

identifying a sub-grid of uniformly-distributed points in the grid, wherein (i) each point in the sub-grid is at least the predefined distance from each edge point in the grid, and (ii) each pair of adjacent points in the grid are separated by the predefined distance;

identifying a first group of points in the sub-grid, wherein the points in the first group are uniformly distributed by a first distance equal to a first multiple of the predefined distance;

for each point in the first group of points, determining a pressure value for that point using one or more reference-level pressures of points that are the first distance from that point;

for each point in the first group of points, determining a pressure difference between the reference-level pressure for that point and the pressure value for that point;

determining if the largest difference from the determined pressure differences is greater than a threshold amount of pressure;

if the largest difference is greater than the threshold amount of pressure, setting the maximum distance for separating two adjacent atmospheric sensors to the first distance; and

if the largest difference is not greater than the threshold amount of pressure, setting the maximum distance to another distance that is larger than the first distance.

2. The method of claim 1 , wherein setting the maximum distance to another distance that is larger than an nth distance comprises:

determining if the number of groups of points that have been identified is less than a threshold number; and

if the number of the groups is not less than the threshold number, the maximum distance for separating two adjacent atmospheric sensors is set to a distance that is greater than the first distance.

3. The method of claim 2 , wherein the distance that is greater than the first distance equals a length of a smallest side of the sub-grid.

4. The method of claim 2 , wherein the distance that is greater than the first distance is a second distance equal to a second multiple of the predefined distance.

5. The method of claim 2 , wherein if the number of the groups is less than the threshold number, the method further comprises:

identifying a second group of points in the sub-grid, wherein the points in the second group are uniformly distributed by a second distance equal to a second multiple of the predefined distance;

for each point in the second group of points, determining a pressure value for that point using one or more reference-level pressures of points that are the second distance from that point;

for each point in the second group of points, determining a pressure difference between the reference-level pressure for that point and the pressure value for that point;

determining if the largest difference from the determined pressure differences is greater than the threshold amount of pressure;

if the largest difference is greater than the threshold amount of pressure, setting the maximum distance for separating two adjacent atmospheric sensors to the second distance; and

if the largest difference is not greater than the threshold amount of pressure, setting the maximum distance to another distance that is larger than the second distance.

6. The method of claim 2 , wherein the threshold number is determined by:

computing a first number that is equal to half a number of edge points on the shortest side of the grid minus one;

if the first number is not a whole number, rounding down the first number to the nearest integer to produce a second number and setting the threshold number to the second number; and

if the first number is not a whole number, setting the threshold number to the first number.

7. The method of claim 1 , wherein determining a pressure value for that point using one or more reference-level pressures of points that are the first distance from that point comprises:

determining an average of reference-level pressures for any combination of two, three or four points that are the first distance from the point; and

setting the pressure value to the determined average.

8. The method of claim 1 , wherein determining a pressure value for that point using one or more reference-level pressures of points that are the first distance from that point comprises:

computing the pressure value using bilinear interpolation of all reference-level pressures for all points that are separated from the point by the first distance.

9. The method of claim 1 , wherein determining a pressure value for that point using one or more reference-level pressures of points that are the first distance from that point comprises:

setting the pressure value as any reference-level pressure of any point that is the first distance from the point.

10. The method of claim 1 , wherein determining a pressure value for that point using one or more reference-level pressures of points that are the first distance from that point comprises:

setting the pressure value as a first reference-level pressure of a point located the first distance from the point that differs most from a reference-level pressure of the point as compared to other reference-level pressures of points that are located the first distance from the point.

11. 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 .

12. A system for determining where to place atmospheric sensors that provide measurements of pressure used to estimate an altitude of a mobile device in an environment, the system comprising one or more machines configured to perform the method of claim 1 .