Abstract: Determining one or more heights of one or more mobile devices above surfaces. Particular embodiments described herein include machines that retrieve first data (e.g., measurement value(s) determined by sensor(s) of a mobile device or estimated position(s) of the mobile device), determine a location context based on the first data, identify second data (e.g., measurement value(s) determined by sensor(s) of the mobile device or status indicator value(s) of feature(s) of the mobile device) to retrieve for use in determining an estimated height above a surface at which the mobile device is located based on the determined location context, retrieve the second data, and determine an estimated height above a surface at which the mobile device is located based on the retrieved second data.

Abstract: Determining when a barometric-based approach for estimating an unknown altitude of a mobile device should not be used. Different approaches determine if estimating an unknown altitude of a mobile device using a measured atmospheric condition will result in an estimated altitude having acceptable or unacceptable error. If use of the measured atmospheric condition would result in acceptable error, the measured atmospheric condition is used to estimate the unknown altitude. If use of the measured atmospheric condition would result in unacceptable error, the measured atmospheric condition is not used to estimate the unknown altitude. The resultant altitude estimate is then used to locate the mobile device.

Abstract: A method involves identifying multiple calibration values and corresponding calibration confidence values of an initial calibration dataset in which one or more calibration values were derived using an atmospheric pressure measurement from a barometric air pressure sensor of a mobile device. A calibration metric is determined for each calibration value. One or more of the calibration values are filtered out from the initial calibration dataset based on the calibration metric to generate a filtered calibration dataset. A filtered calibration value is determined using the filtered calibration dataset. The barometric air pressure sensor of the mobile device is calibrated using the filtered calibration value.

Abstract: An alert indicates that a situation conducive to calibrating a barometric pressure sensor of the user device might have occurred. In response, calibration data is collected for calibrating the barometric pressure sensor. The calibration data is used to perform a calibration process and generate a calibration value for the barometric pressure sensor.

Abstract: Determining calibration values for atmospheric sensors that provide measured pressures used for estimating altitudes of mobile devices. Particular systems and methods determine if any uncalibrated reference-level pressure estimates associated with an unstable pressure sensor should not be used when calibrating the unstable pressure sensor, and calibrate the unstable pressure sensor using all of the uncalibrated reference-level pressure estimates except any uncalibrated reference-level pressure estimate that should not be used when calibrating the unstable pressure sensor.

Abstract: Determining contexts of mobile devices. Particular embodiments described herein include machines that determine two estimated positions of a mobile device that respectively correspond to first and second locations at first and second times, acquire sets of terrain or structural information for first and second areas that respectively include the first and second estimated positions, use the acquired sets of information and the estimated positions to determine if the mobile device was near or within a structure at the first and second times, determine one or more values that are indicative of vertical movement by the mobile device during a period of time between the first time and the second time, compare the one or more values to one or more threshold conditions, and determine a context of the mobile device based on the comparison.

Abstract: Multiple calibration results for calibrating a barometric pressure sensor based on data received from a device containing the sensor are determined and stored in a table. The table is updated based on rules regarding a relationship between each calibration result and a current calibration value. The calibration results are weighted and combined to determine a combined calibration result. The calibration value for calibrating the sensor is selected from the calibration results, the combined calibration results, or the current calibration value based on a selection criteria.

Abstract: Determining, broadcasting and using reference pressure data in a network of transmitters. Particular embodiments described herein include machines that select atmospheric data from weather stations within a transmitter network, use the selected atmospheric data to determine a reference atmospheric value, and transmit the reference atmospheric value from a transmitter to a mobile device for use in estimating an altitude of the mobile device. The atmospheric data may include any of reference pressures form the weather stations, measured temperatures from the weather stations, or reference temperatures from the weather stations. The reference atmospheric value may include a reference pressure value of a reference altitude, or a reference temperature value.

Abstract: Field calibration of a pressure device involves collecting simultaneous pressure data or pressure and temperature data at two devices for multiple time points. Pressure differences between pairs of simultaneous data points of the collected pressure data are calculated. A model is fitted to the pressure differences and the temperatures and/or pressures, and model parameters are used to correct measurements from the second device. Alternatively, a pressure gradient is estimated for a region that encompasses the two devices for each time point. A distance is determined between the two devices. A pressure gradient difference is determined between the two devices for each time point. A pressure difference offset is obtained for one of the pairs of simultaneous data points for each time point. An average pressure difference offset is determined between the two devices and is used to correct measurements from one of the devices.

Abstract: A method involves determining an estimated position of a mobile device within a region. Atmospheric data measurement stations are identified within the region. A geographical anomaly is identified within the region that physically intervenes between the mobile device and a first atmospheric data measurement station. Based on a positional relationship between the mobile device, the geographical anomaly, and the first atmospheric data measurement station, it is determined that atmospheric pressure measurements collected at the first atmospheric data measurement station should be conditionally used for determining a reference pressure estimate. The reference pressure estimate is determined using a plurality of atmospheric pressure measurements collected at the atmospheric data measurement stations and conditionally using the atmospheric pressure measurements collected at the first atmospheric data measurement station.

Abstract: Embodiments describe determining position by selecting a set of digital pseudorandom sequences. The magnitudes of the cross-correlation between any two sequences of the chosen set are below a specified threshold. A subset of digital pseudorandom sequences are selected from the set such that the magnitudes of the autocorrelation function of each member of the subset, within a specified region adjacent to the peak of the autocorrelation function, are equal to or less than a prescribed value. Each transmitter transmits a positioning signal, and at least a portion of the positioning signal is modulated with at least one member of the subset. At least two transmitters of the plurality of transmitters modulate respective positioning signals with different members of the subset of digital pseudorandom sequences.

Abstract: Determining when a barometric-based approach for estimating an unknown altitude of a mobile device should not be used. Different approaches determine if estimating an unknown altitude of a mobile device using a measured atmospheric condition will result in an estimated altitude having acceptable or unacceptable error. If use of the measured atmospheric condition would result in acceptable error, the measured atmospheric condition is used to estimate the unknown altitude. If use of the measured atmospheric condition would result in unacceptable error, the measured atmospheric condition is not used to estimate the unknown altitude. The resultant altitude estimate is then used to locate the mobile device.

Abstract: A method to identify a problematic 2D position of a mobile device can include: determining a reported 2D position of the mobile device; determining a piece of information about the mobile device; and comparing the reported 2D position and the piece of information about the mobile device. Upon determining that the reported 2D position and the piece of information about the mobile device are consistent with each other, the reported 2D position of the mobile device is used as an estimate of the actual 2D position of the mobile device, or upon determining that the reported 2D position and the piece of information about the mobile device are not consistent with each other, the reported 2D position is determined to be problematic, and the reported 2D position of the mobile device is removed from a list of reported 2D positions of the mobile device.

Abstract: Determining when an estimated altitude of a mobile device can be used for calibration or location determination. Particular systems and methods determine an area in which the mobile device is expected to reside, determine an altitude value of each section of a plurality of sections in the area, determine if the altitude values meet a threshold condition, and determine that the estimated altitude of the mobile device can be used for determining the position of the mobile device or for calibrating a pressure sensor of the mobile device when the altitude values meet the threshold condition.

Abstract: Pressure-based estimation of a mobile device altitude or calibration of a pressure sensor involves machines that determine if a reference-level pressure value based on one or more measurements of pressure from a network of weather stations should or should not be used to calibrate a pressure sensor of a mobile device or to estimate an altitude of the mobile device. If the reference-level pressure value should be used, the reference-level pressure value is used to calibrate a pressure sensor of a mobile device or to estimate an altitude of the mobile device. If the reference-level pressure value should not be used, a trend in pressure is determined, an estimated reference-level pressure value based on the trend is determined, and the estimated reference-level pressure value is used to calibrate a pressure sensor of a mobile device or to estimate an altitude of the mobile device.

Abstract: A calculated current lapse rate is determined for a geographical area that includes a location of a mobile device. The calculated current lapse rate provides an estimated air temperature variation with respect to altitude variation for the location of the mobile device. An altitude of the mobile device is estimated. An uncertainty of the altitude of the mobile device is estimated based on a reference pressure and a reference temperature for a reference plane that is within the geographical area, a device pressure for the mobile device, and the calculated current lapse rate.

Abstract: Determining, broadcasting and using reference pressure data in a network of transmitters. Particular embodiments described herein include machines that select atmospheric data from weather stations within a transmitter network, use the selected atmospheric data to determine a reference atmospheric value, and transmit the reference atmospheric value from a transmitter to a mobile device for use in estimating an altitude of the mobile device. The atmospheric data may include any of reference pressures form the weather stations, measured temperatures from the weather stations, or reference temperatures from the weather stations. The reference atmospheric value may include a reference pressure value of a reference altitude, or a reference temperature value.

Abstract: Multiple calibration results for calibrating a barometric pressure sensor based on data received from a device containing the sensor are determined and stored in a table. The table is updated based on rules regarding a relationship between each calibration result and a current calibration value. The calibration results are weighted and combined to determine a combined calibration result. The calibration value for calibrating the sensor is selected from the calibration results, the combined calibration results, or the current calibration value based on a selection criteria.

Abstract: Extending the spatial coverage of a reference pressure network. Particular embodiments described herein include machines that initially determine that an estimated position of a mobile device resides outside a coverage area of a network of reference pressure sensors. Reference-level pressures corresponding to reference pressure sensors of the network are determined using measurements of pressure from the network of reference pressure sensors. A pressure pattern for a region that includes the estimated position and an area not included in the coverage area of the network is determined using reference-level pressures that were not determined using measurements of pressure from the network of reference pressure sensors. The reference-level pressures corresponding to reference pressure sensors of the network and the pressure pattern are used 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.

Abstract: A wholistic activity context is used to determine whether to calibrate a barometric pressure sensor of a mobile device. A pair of activity transitions are determined from three activities of the mobile device. A time relationship and a position relationship between the activity transitions is determined. An opportunity to calibrate the barometric pressure sensor occurs between the activity transitions. A calibration of the barometric pressure sensor is performed in response to determining that the time relationship and the position relationship indicate that the wholistic activity context surrounding the opportunity to calibrate the barometric pressure sensor is conducive to calibration.