Abstract:
The disclosure includes a system, method and tangible memory for providing application assurance for an open platform in-vehicle infotainment system. The system includes an open platform in-vehicle infotainment system including a tangible memory, a processor and an untrusted application including a monitor module. The untrusted application is stored in the tangible memory. The monitor module included in the untrusted application is generated based on a set of one or more runtime rules describing desired behavior of the untrusted application that complies with a specification for an application programming interface of the open platform in-vehicle infotainment system. The untrusted application runs on the open platform in-vehicle infotainment system. The monitor module causes the processor to observe, based on the one or more runtime rules, behavior of the untrusted application to determine whether the observed behavior of the untrusted application is consistent with the desired behavior of the untrusted application.

Description:
BACKGROUND 
       [0001]    The specification relates to a mobile computer atmospheric barometric pressure system. 
         [0002]    Barometric pressure is the pressure exerted by the weight of air in the atmosphere of Earth. In some circumstances barometric pressure is closely approximated by the hydrostatic pressure caused by the weight of air above some predetermined measurement point. On a given plane, low-pressure areas have less atmospheric mass above their location, whereas high-pressure areas have more atmospheric mass above their location. Likewise, as elevation increases, there is less overlying atmospheric mass. Atmospheric pressure is related to the overlying mass. Atmospheric pressure generally decreases with increasing elevation. On average, a column of air one square centimeter in cross-section, measured from sea level to the top of the atmosphere, has a mass of about 1.03 kilogram (kg) and weight of about 10.1 Newtons (N). A column one square inch in cross-section would have a weight of about 14.7 pounds (lbs) or about 65.4 N. Barometric pressure is sometimes called atmospheric pressure. For the purpose of clarity, the term “barometric pressure” is used in this disclosure. 
       SUMMARY 
       [0003]    The subject matter described in this disclosure includes a mobile computer atmospheric barometric pressure system (herein “the system” or “the barometric pressure system”) described according to some implementations. In some implementations, the barometric pressure system may be an element of a vehicle or a mobile device. 
         [0004]    The vehicle may include a special-purpose computing device. For example, the vehicle may include an onboard vehicle computer that includes hardware and software specially designed and manufactured to meet the needs of the onboard vehicle computer so that the vehicle provides a safe and desirable user experience that conforms to federal and local regulations (e.g., safety, air emissions, Federal Communication Commission regulation of wireless transmissions, etc.). 
         [0005]    The mobile device may include a processor-based computing device. For example, the mobile device may include a smartphone, tablet computer, laptop, smartwatch, Internet-of-Things device, personal computer, stationary roadside device, etc. The mobile device may include a processor. The processor may be programmed to provide some or all of the functionality described herein with reference to the system. In this way, the mobile device may be a special-purpose computing device programmed to provide the functionality described herein with reference to the system. 
         [0006]    The vehicle or the mobile device may include an alarm system. The alarm system may include a processor based computing device or be an element of a processor based computing device. For example, the alarm system may be an element of the onboard vehicle computer. The alarm system may also be an element of a smartphone or some other mobile device. 
         [0007]    In some implementations, the alarm system may be configured to analyze sensor data and determine whether the vehicle or the mobile device is on a trajectory that will result in a collision with an object on the roadway. The sensor data may include data describing measurements detected and recorded by one or more electronic sensor devices of the vehicle or the mobile device. The object may be another vehicle or any other object on the roadway. 
         [0008]    The alarm system may be configured to provide a collision threat alarm to a driver of the vehicle or a user of the mobile device. The alarm system may provide the collision threat alarm if the vehicle or the mobile device is determined to be on a trajectory that will result in a collision. The collision threat alarm may include providing an audible signal to the driver (or the user), a visual signal to the driver (or the user) or a combination of an audible and visual signal to the driver (or the user). Proving the collision threat alarm to the driver (or the user) may be referred to as a collision threat alarm incident. 
         [0009]    The alarm system may be configured to provide automated mitigation actions by onboard systems or recommendations to an autonomous driving controller in response to an alarm condition. The barometric pressure system may be configured to improve the performance or operation of the alarm system. For example, assume that the barometric pressure system is an element of a vehicle. The sensor data may include data describing the location, speed and trajectory of the vehicle at a specified time. The sensor data may also include data describing the location, speed and trajectory of the object on the roadway. The sensor data may include location data indicating the latitude and longitude coordinates for the vehicle and the object as indicated by one or more global positioning systems. The sensor data may also include elevation data describing the elevations of the vehicle and the object as indicated by the one or more global positioning systems. The alarm system may analyze the sensor data and determine that a collision will occur between the vehicle and the object. However, the latitude and longitude data do not indicate the relative altitude of the vehicle and the object. The global positioning system may provide sensor data describing inaccurate elevation positioning data. Even if the sensor data received from the global positioning system were accurate, wireless communication with the global positioning system may suffer reception disruptions. If the vehicle is driving on a surface road and the object is driving on an overpass directly above the vehicle and the surface road, the latitude and longitude data may indicate that the vehicle and the object are on a collision course with one another. In these situations the alarm system may provide a collision threat alarm if accurate elevation data is not available from GPS. However, in this example the collision threat alarm is erroneous because the vehicle and the object are located at different altitudes, and so, the vehicle and the object will not collide with one another. 
         [0010]    The barometric pressure system described herein improves the performance of the alarm system by ensuring that such erroneous alarms do not occur. For example, the barometric pressure system may include a barometric pressure sensor to measure and record the barometric pressure for the vehicle. The barometric pressure difference between systems relates to the altitude differences of the systems. Forces such as acceleration of the system may cause the reading of the barometric pressure to be inaccurate. The barometric pressure system may include one or more electronic sensor devices to record the acceleration or roadway noise. The barometric pressure system may include processors that are programmed to adjust the measured barometric pressure to account for these forces and achieve an accurate measurement of the barometric pressure. The adjusted measurement of the barometric pressure may be referred to herein as an “acceleration-adjusted reading of the barometric pressure,” an “acceleration-adjusted reading of the first barometric pressure,” an “acceleration-adjusted reading of the second barometric pressure” or some similar terminology. 
         [0011]    Other forces which may be measured and adjusted for include roadway noise. The roadway noise may include the noise and vibration caused by nearby vehicles that are passing the vehicle. For example, the roadway noise may include the noise and vibration caused in a smaller vehicle when a heavy truck passes the smaller vehicle. 
         [0012]    Other benefits of the barometric pressure system are described herein and will be apparent based on the description. 
         [0013]    Described according to some implementations is a barometric pressure system that includes a wireless communication network (communication network) which communicatively couples a first vehicle and a second vehicle. The second vehicle may be traveling in the same direction as the first vehicle. The second vehicle may be located in a different lane relative to the first vehicle while still traveling in the same direction as the first vehicle. For example, the first vehicle may be located in the first lane or a northbound roadway. The second vehicle may be located in the second lane of the northbound roadway. 
         [0014]    The second vehicle includes an alarm system. The alarm system may be configured to analyze sensor data of the second vehicle and determine whether the second vehicle is on a trajectory that will result in the second vehicle colliding with an object on the roadway. The object may be another vehicle or any other object on the roadway. The alarm system is configured to provide a collision threat alarm to a driver of the second vehicle if the second vehicle is determined to be on a trajectory that will result in the second vehicle colliding with an object on the roadway. The collision threat alarm may include providing an audible signal to the driver, a visual signal to the driver or a combination of an audible and visual signal to the driver. Proving the collision threat alarm to the driver may be referred to as a collision threat alarm incident. 
         [0015]    The first vehicle includes a set of first electronic sensor devices, a second electronic sensor device and a first onboard vehicle computer. The set of first electronic sensor devices are configured to record first barometric pressure data describing a first barometric pressure associated with the first vehicle. The second electronic sensor device is configured to record acceleration data describing an acceleration of the first vehicle. 
         [0016]    The first onboard vehicle computer is communicatively coupled to the DSRC communication network, the set of first electronic sensor devices and the second electronic sensor device. The first onboard vehicle computer is programmed to (1) adjust the first barometric pressure data based on the acceleration of the first vehicle so that the first barometric pressure data describes an acceleration-adjusted reading of the first barometric pressure associated with the first vehicle and (2) automatically transmit the first barometric pressure data describing the acceleration-adjusted reading to a selected channel of the DSRC communication network. 
         [0017]    The second vehicle includes a second onboard vehicle computer. The second onboard vehicle computer is communicatively coupled to the selected channel of the DSRC communication network. The second onboard vehicle computer is programmed to receive the first barometric pressure data describing the acceleration-adjusted reading. The second onboard vehicle computer is programmed to determine an estimate of altitude separation based on the first barometric pressure data and second barometric pressure data describing a second barometric pressure associated with the second mobile device. 
         [0018]    The estimate of altitude separation describes an estimate of whether the first vehicle and the second vehicle are located at substantially the same altitude. The second onboard vehicle computer is programmed to suppress a collision threat alarm based on the estimate of altitude separation indicating that the first vehicle and the second vehicle are not located at substantially the same altitude. 
         [0019]    The altitude separation may be based on the differential barometric pressure between the first mobile device and the second mobile device. In other words, the altitude separation may be determined by subtracting the lower of the two barometric pressures from the higher of the two barometric pressures to determine the differential barometric pressure between the first mobile device and the second mobile device. The differential barometric pressure and the estimate of the altitude separation may be directly proportional in that the closer the differential barometric pressure is to zero, the closer the estimate of altitude separation is to zero. An estimated altitude separation equal to zero indicates that the two objects are located at substantially the same altitude. If the first vehicle and the second vehicle are located at substantially the same altitude and also on a collision course, then the collision threat alarm is not suppressed. 
         [0020]    Also described according to some implementations is a barometric pressure system of a mobile device. The barometric pressure system includes: a wireless network communicatively coupled to the mobile device; a first electronic sensor device configured to record barometric pressure data describing a barometric pressure associated with the mobile device; a second electronic sensor device configured to record acceleration data describing an acceleration of the mobile device; and a processor communicatively coupled to the wireless network, the first electronic sensor device and the second electronic sensor device. 
         [0021]    The processor is programmed to adjust the barometric pressure data based on the acceleration of the mobile device so that the barometric pressure data describes an acceleration-adjusted reading of the barometric pressure associated with the mobile device. The processor is also programmed to automatically transmit the barometric pressure data describing the acceleration-adjusted reading to the wireless network. The processor is programmed to transmit the barometric pressure data to the wireless network in substantially real time. For example, the processor may be programmed to transmit the barometric pressure data to the wireless network in every 0.1 seconds. In some implementations, the processor may be programmed to transmit the barometric pressure data to the wireless network in a time interval configured by the processor to avoid a collision threat alarm incident. 
         [0022]    Also described according to some implementations is a barometric pressure system of a mobile device including a wireless network communicatively coupled to the mobile device. The barometric pressure system may include a set of first electronic sensor devices configured to record barometric pressure data describing a barometric pressure associated with the mobile device. The barometric pressure system may include a second electronic sensor device configured to record acceleration data describing an acceleration of the mobile device. The barometric pressure system may also include a processor communicatively coupled to the wireless network, the set of first electronic sensor devices and the second electronic sensor device. 
         [0023]    The processor is programmed to (1) determine quality data describing a quality of the barometric pressure data and (2) adjust the barometric pressure data based on the quality of the barometric pressure data and the acceleration of the mobile device so that the barometric pressure data describes a quality and acceleration-adjusted reading of the barometric pressure associated with the mobile device. The processor is also programmed to automatically transmit the barometric pressure data describing the acceleration-adjusted reading to the wireless network. 
         [0024]    The quality and acceleration-adjusted reading of the barometric pressure may indicate a measurement of the barometric pressure that is adjusted to account for (1) barometric pressure sensors that may require calibration as indicated by the quality data and (2) the effect of acceleration forces on the ability of a barometric pressure sensor to measure barometric pressure. 
         [0025]    In some implementations, the quality data may be based on one or more of (1) time to live data associated with the set of first electronic sensor devices and describing an estimate of how long the set of first electronic sensor devices are estimated to live and (2) time since calibration data associated with the set of first electronic sensor devices and describing how long since the set of first electronic sensor devices was calibrated. 
         [0026]    In some implementations, the barometric pressure sensor may include a MicroElectroMechancial (MEMS) sensor. The barometric pressure data may be determined based on MEMS sensor deflection and the temperature of the MEMS sensor. Deflection nonlinearity may indicate inaccuracy in the readings of the MEMS sensor. The nonlinearity may be corrected using calibration data determined based on a calibrated pressure source and a temperature reading taken from the onboard temperature sensor of the vehicle. The MEMS sensor may include a non-transitory, non-volatile memory. The calibration data may be stored in the memory of the MEMS sensor. 
         [0027]    Also described according to some implementations is a barometric pressure system including a wireless network communicatively coupled to a first mobile device and a second mobile device. The first mobile device includes a set of first electronic sensor devices, a second electronic sensor device and a first processor. The set of first electronic sensor devices are configured to record first barometric pressure data describing a first barometric pressure associated with the first mobile device. The second electronic sensor device is configured to record acceleration data describing an acceleration of the first mobile device. 
         [0028]    The first processor is communicatively coupled to the wireless network, the set of first electronic sensor devices and the second electronic sensor device. The first processor is programmed to (1) adjust the first barometric pressure data based on the acceleration of the first mobile device so that the first barometric pressure data describes an acceleration-adjusted reading of the first barometric pressure associated with the first mobile device and (2) automatically transmit the first barometric pressure data describing the acceleration-adjusted reading to the wireless network. 
         [0029]    The second mobile device is communicatively coupled to the wireless network and configured to receive the first barometric pressure data describing the acceleration-adjusted reading. The second mobile device is configured to determine an estimate of altitude separation based on the first barometric pressure data and second barometric pressure data describing a second barometric pressure associated with the second mobile device. The estimate of altitude separation describes an estimate of whether the first mobile device and the second mobile device are located at substantially the same altitude. 
         [0030]    In some implementations, the estimate of altitude separation describes a delta in altitude for the first mobile device and the second mobile device. In some implementations, at least one of the first mobile device and the second mobile device is a vehicle. 
         [0031]    In some implementations, the first mobile device includes a subsystem configured to determine a first geographic location vector based on (1) a first location of the first mobile device at a first time, (2) a first speed of the first mobile device, (3) and a first direction of the first mobile device and (4) the first barometric pressure data describing the acceleration-adjusted reading. The first geographic location vector may include vector data describing the location of the first mobile device (e.g., the first location) at a first time (e.g., a specified time), the speed of the first mobile device, the direction of travel of the first mobile device and the acceleration-adjusted reading of the barometric pressure associated with the first mobile device while present at the location or substantially at the first location. The first mobile device transmits the first geographical location vector to the wireless network. 
         [0032]    The second mobile device receives the first geographical location vector from the wireless network. The second mobile device includes a second processor that is programmed to determine a second geographic location vector based on (1) a second location of the second mobile device at a second time, (2) a second speed of the second mobile device; (3) a second direction of the second mobile device and (4) the second barometric pressure data associated with the second mobile device. The second geographic location vector may include vector data describing the location of the second mobile device (e.g., the second location) at a second time (e.g., a specified time), the speed of the second mobile device, the direction of travel of the second mobile device and the acceleration-adjusted reading of the barometric pressure associated with the second mobile device while present at the location or substantially at the second location. 
         [0033]    The second processor is further programmed to determine an estimate of whether the first mobile device and the second mobile device will collide based on the first geographical location vector, the second geographical location vector and the estimate of altitude separation. 
         [0034]    In some implementations, the first geographical location vector and the second geographical location vector indicate that the first mobile device and the second mobile device will collide but the second processor determines that the first mobile device and the second mobile device will not collide based on a determination that the estimate of altitude separation indicates that the first mobile device and the second mobile device are not located at substantially the same altitude. 
         [0035]    In some implementations, the second processor of the second mobile device suppresses a collision threat alarm based on a determination that the first mobile device and the second mobile device will not collide because they are not located at substantially the same altitude. 
         [0036]    Also described according to some implementations is a barometric pressure system of a vehicle including a plurality of electronic sensor devices configured to record first barometric pressure data describing a first barometric pressure associated with the vehicle. Each of the electronic sensor devices records a separate barometric pressure reading associated with the vehicle. 
         [0037]    The barometric pressure system of the vehicle also includes an onboard vehicle computer that is communicatively coupled to the plurality of electronic sensor devices and programmed to (1) analyze the separate barometric pressure readings associated with the plurality of electronic sensor devices to determine, for each of the electronic sensor devices, a confidence factor indicating confidence in the accuracy of the barometric pressure reading for each of the electronic sensor devices and (2) determine whether to provide a sensor service recommendation based on the confidence factor. 
         [0038]    In some implementations, the onboard vehicle computer is programmed to analyze variation of the separate barometric pressure readings among the plurality of electronic sensor devices to determine the confidence factor. 
         [0039]    In some implementations, the confidence factor is based in part on one or more of (1) time to live data associated with the plurality of electronic sensor devices and describing an estimate of how long the plurality of electronic sensor devices are estimated to live and (2) time since calibration data associated with the plurality of electronic sensor devices and describing how long since the plurality of electronic sensor devices was calibrated. 
         [0040]    In some implementations, the barometric pressure system also includes a wireless network and a mobile device. The vehicle and the mobile device are communicatively coupled to the wireless network and the vehicle receives second barometric pressure data describing a second barometric pressure reading associated with the mobile device. The onboard vehicle computer is programmed to (1) analyze the second barometric pressure reading associated with the mobile device and the separate barometric pressure readings associated with the plurality of electronic sensor devices to determine, for each of the electronic sensor devices, the confidence factor indicating confidence in the accuracy of the barometric pressure reading for each of the electronic sensor devices and (2) determine whether to provide the sensor service recommendation based on the confidence factor. 
         [0041]    The second mobile device is communicatively coupled to the wireless network and configured to receive the first barometric pressure data describing the acceleration-adjusted reading and determine an estimate of altitude separation based on the first barometric pressure data and second barometric pressure data describing a second barometric pressure associated with the second mobile device. The estimate of altitude separation describes an estimate of whether the first mobile device and the second mobile device are located at substantially the same altitude. 
         [0042]    Also described according to some implementations is a barometric pressure system of a mobile device configured to determine the location of the mobile device based on an acceleration-adjusted barometric pressure. The barometric pressure system includes a non-transitory storage medium storing altitude map data. The altitude map data describes an altitude map for a geographic area and a plurality of altitudes associated with a plurality of locations included in the geographic area. The barometric pressure system also includes a global positioning system configured to determine location data describing an estimate of a location of the mobile device. The barometric pressure system also includes a set of first electronic sensor devices configured to record barometric pressure data describing a barometric pressure associated with the mobile device. The barometric pressure system also includes a second electronic sensor device configured to record acceleration data describing an acceleration of the mobile device. 
         [0043]    The barometric pressure system also includes a processor communicatively coupled to the non-transitory storage medium, the global positioning system, the set of first electronic sensor devices and the second electronic sensor device. The processor is programmed to (1) adjust the barometric pressure data based on the acceleration of the mobile device so that the barometric pressure data describes an acceleration-adjusted reading of the barometric pressure associated with the mobile device, (2) determine an altitude-based geographic location of the mobile device by analyzing the altitude map to identify a location having an altitude indicated by the barometric pressure data and (3) adjust the location data based on the altitude-based geographic location so that the location data more accurately describes the location of the mobile device. 
         [0044]    Also described according to some implementations is a barometric pressure system of a vehicle configured to automatically generate an altitude map for a lane of a roadway in a geographic area based on an acceleration-adjusted barometric pressure. The barometric pressure system includes a global positioning system configured to determine location data describing an estimate of a location of the vehicle. The barometric pressure system also includes a roadway imaging device configured to determine which lane the vehicle is located in while at the location. The barometric pressure system also includes a set of first electronic sensor devices configured to record barometric pressure data describing a barometric pressure associated with the vehicle. The barometric pressure system also includes a second electronic sensor device configured to record acceleration data describing an acceleration of the vehicle. 
         [0045]    The barometric pressure system also includes an onboard vehicle computer communicatively coupled to a non-transitory storage medium, the global positioning system, the roadway imaging device, the set of first electronic sensor devices and the second electronic sensor device. The onboard vehicle computer is programmed to (1) adjust the barometric pressure data based on the acceleration of the vehicle so that the barometric pressure data describes an acceleration-adjusted reading of the barometric pressure associated with the vehicle, (2) adjust the location data to include the lane the vehicle was located in while at the location, (3) determine an altitude for the lane based on the first barometric pressure data and (4) store altitude map data in the non-transitory memory describing the location data and the altitude for the lane the vehicle was located in while at the location. 
         [0046]    In some implementations, the onboard vehicle computer is further programmed to generate a geographic location vector for the vehicle based on one or more of: (1) the location data; (2) a first speed of the vehicle; (3) the barometric pressure data describing the acceleration-adjusted reading of the barometric pressure associated with the vehicle; (4) the altitude map data; (5) a current time; (6) a direction of the vehicle and (7) the an acceleration of the vehicle. 
         [0047]    Also described according to some implementations is a barometric pressure system of a vehicle configured to automatically steer the vehicle based on an acceleration-adjusted barometric pressure. The barometric pressure system includes a non-transitory storage medium storing altitude map data. The altitude map data describes an altitude map for a geographic area and a plurality of altitudes associated with a plurality of lane locations included in the geographic area. The barometric pressure system also includes a global positioning system configured to determine location data describing an estimate of a location of the vehicle. The barometric pressure system also includes a roadway imaging device configured to determine which lane the vehicle is located in while at the location and detect an instance where a trajectory of the vehicle will cause the vehicle to leave the lane without authorization if not corrected. The barometric pressure system also includes a set of first electronic sensor devices configured to record barometric pressure data describing a barometric pressure reading associated with the vehicle. The barometric pressure system also includes a second electronic sensor device configured to record acceleration data describing an acceleration of the vehicle. 
         [0048]    The barometric pressure system also includes an onboard vehicle computer communicatively coupled to the global positioning system, the roadway imaging device, the set of first electronic sensor devices and the second electronic sensor device. The onboard vehicle computer is programmed to (1) adjust the barometric pressure data based on the acceleration of the vehicle so that the barometric pressure data describes an acceleration-adjusted reading of the barometric pressure associated with the vehicle, (2) determine an altitude-based geographic location of the vehicle by analyzing the altitude map to identify a location having an altitude indicated by the barometric pressure data, (3) adjust the location data based on the altitude-based geographic location so that the location data more accurately describes the location of the vehicle and which lane the vehicle is located in while at the location, (4) determine a corrective action including which direction to steer the vehicle so that the trajectory of the vehicle will cause the vehicle to remain in the lane and (5) cause the vehicle to be steered based on the corrective action so that the trajectory of the vehicle will cause the vehicle to remain in the lane. 
         [0049]    Also described according to some implementations is a barometric pressure system including a wireless network communicatively coupled to a first mobile device and a second mobile device which is located at substantially the same altitude as the first mobile device. The first mobile device includes a set of first electronic sensor devices, a second electronic sensor device and a first processor. The barometric pressure system also includes a non-transitory memory. The set of first electronic sensor devices are configured to record first barometric pressure data describing a first barometric pressure reading associated with the first mobile device. The second electronic sensor device is configured to record acceleration data describing an acceleration of the first mobile device. 
         [0050]    The first processor is communicatively coupled to the wireless network, the non-transitory memory, the set of first electronic sensor devices and the second electronic sensor device. The first processor is programmed to adjust the first barometric pressure data based on the acceleration of the first mobile device so that the first barometric pressure data describes an acceleration-adjusted reading of the first barometric pressure associated with the first mobile device. 
         [0051]    The second mobile device is communicatively coupled to the wireless network. The second mobile device is configured to transmit second barometric pressure data describing a second barometric pressure associated with the second mobile device. 
         [0052]    The first processor, which is communicatively coupled to the wireless network, is programmed to receive the second barometric pressure data from the wireless network. The first processor is programmed to determine a variance between the first barometric pressure and the second barometric pressure. 
         [0053]    The non-transitory memory stores a plurality of historical variances determined based on a plurality of second barometric pressure data received from a plurality of second mobile devices. The first processor is programmed to analyze the variance and the historical variance to determine an adjustment for the acceleration-adjusted reading of the first barometric pressure so that the acceleration-adjusted reading of the first barometric pressure is more accurate. 
         [0054]    In some implementations, the first mobile device is a first vehicle and the second mobile device is a second vehicle that is traveling in the same direction as the first vehicle and passing the first vehicle. For example, the first mobile device is heading in a northbound direction in lane one of a freeway. The second mobile device is also heading in the northbound direction in lane two of the same freeway. The second mobile device is traveling at a faster speed than the first mobile device so that the second mobile device is passing the first mobile device. 
         [0055]    In some implementations, the first processor is programmed to (1) determine vehicle motion and air flow noise associated with the second vehicle passing the first vehicle, (2) determine an effect of the vehicle motion and air flow noise on the acceleration-adjusted reading of the first barometric pressure associated with the first vehicle and (3) modify the acceleration-adjusted reading of the first barometric pressure so that the effect is filtered from the acceleration-adjusted reading of the first barometric pressure. 
         [0056]    In some implementations, the first processor applies signal processor to filter the effect from the acceleration-adjusted reading of the first barometric pressure. 
         [0057]    In some implementations, the set of first electronic sensor devices and the second electronic sensor device are mounted in the first mobile device in a configuration designed to reduce the effect of the of the vehicle motion and air flow noise on the acceleration-adjusted reading of the first barometric pressure associated with the first mobile device. 
         [0058]    In some implementations, the barometric pressure system includes a third mobile device. The third mobile device is communicatively coupled to the wireless network. The third mobile device is configured to transmit third barometric pressure data describing a third barometric pressure associated with the third mobile device. The third barometric pressure data may be transmitted to the wireless network. 
         [0059]    The first processor is programmed to receive the third barometric pressure data from the wireless network and determine a variance among the first barometric pressure, the second barometric pressure and the third barometric pressure. The first processor is programmed to analyze (1) the variance associated with the first barometric pressure, the second barometric pressure and the third barometric pressure and (2) the historical variance to determine an adjustment for the acceleration-adjusted reading of the first barometric pressure so that the acceleration-adjusted reading of the first barometric pressure is more accurate. 
         [0060]    In some implementations, the third mobile device is a stationary roadside device. For example, the third mobile device is an element of a traffic signal, a pedestrian crosswalk signal, a roadway camera system configured to monitor and determine traffic flow or detect traffic ordinance violations, a special-purpose device configured to provide the functionality of the third mobile device, or any other processor-based computing device mounted along a roadway. 
         [0061]    Also described according to some implementations is a barometric pressure system of a vehicle configured to determine three dimensional location data describing the three dimensional location of the vehicle. The barometric pressure system includes a non-transitory storage medium storing altitude map data. The altitude map data describes an altitude map for a geographic area and a plurality of known barometric pressures associated with a plurality of locations included in the geographic area. The barometric pressure system includes a global positioning system configured to determine location data describing an estimate of a location of the vehicle. The barometric pressure system includes a roadway imaging device configured to determine one or more items of interest surrounding the vehicle. The barometric pressure system includes a set of first electronic sensor devices configured to record barometric pressure data describing a barometric pressure reading associated with the vehicle. The barometric pressure system includes a second electronic sensor device configured to record acceleration data describing an acceleration of the vehicle. 
         [0062]    The barometric pressure system includes an onboard vehicle computer communicatively coupled to the global positioning system, the roadway imaging device, the set of first electronic sensor devices and the second electronic sensor device. The onboard vehicle computer is programmed to (1) adjust the barometric pressure data based on the acceleration of the vehicle so that the barometric pressure data describes an acceleration-adjusted reading of the barometric pressure associated with the vehicle and (2) determine the three dimensional location data describing the three dimensional location of a vehicle based on the (a) one or more items of interest surrounding the vehicle matching one or more known items of interest associated with the estimate of the location of the vehicle and (b) the acceleration-adjusted reading of the barometric pressure associated with the vehicle matching a known barometric pressure and a location associated with the matching known barometric pressure included in the altitude map. 
         [0063]    Also described according to some implementations is a barometric pressure system of a vehicle including a wireless network communicatively coupled to the vehicle and a mobile device. The vehicle includes a first set of electronic sensor devices, a second electronic sensor device and an onboard vehicle computer. The set of first electronic sensor devices is configured to record first barometric pressure data describing a first barometric pressure reading associated with the vehicle. The second electronic sensor device configured to record acceleration data describing an acceleration of the vehicle. The vehicle and the mobile device are communicatively coupled to the wireless network. The mobile device transmits second barometric pressure data describing a second barometric pressure reading associated with the mobile device. 
         [0064]    The onboard vehicle computer is communicatively coupled to the wireless network, the set of first electronic sensor devices and the second electronic sensor device. The onboard vehicle computer is programmed to (1) adjust the first barometric pressure data based on the acceleration of the vehicle so that the first barometric pressure data describes an acceleration-adjusted reading of the first barometric pressure associated with the vehicle, (2) determine a variance between the second barometric pressure reading and the acceleration-adjusted reading of the first barometric pressure associated with the vehicle, (3) determine lateral differential data describing a lateral distance from the vehicle and the mobile device based on the variance and (4) determine an estimate of altitude separation between the vehicle and the mobile device based on the lateral differential data. 
         [0065]    In some implementations, the barometric pressure system of the vehicle further comprises one or more third electronic sensor devices configured to measure and record temperature and humidity associated with the vehicle. In these implementations, the onboard vehicle computer is further programmed to adjust the first barometric pressure data based on the acceleration, the temperature and the humidity of the vehicle. 
         [0066]    In some implementations, the barometric pressure system is further configured to determine whether to trigger a collision threat alarm based at least in part on the lateral differential data and the estimate of altitude separation between the vehicle and the mobile device. 
         [0067]    Other aspects may include corresponding methods, apparatus, and computer program products. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0068]    The disclosure is illustrated by way of example, and not by way of limitation in the figures of the accompanying drawings in which like reference numerals are used to refer to similar elements. 
           [0069]      FIG. 1  is a block diagram illustrating an example operating environment for providing the barometric pressure system. 
           [0070]      FIG. 2A  is a block diagram illustrating an example barometric pressure system. 
           [0071]      FIG. 2B  is a block diagram illustrating an example of environment data. 
           [0072]      FIG. 2C  is a block diagram illustrating an example of motion data. 
           [0073]      FIG. 3  is a block diagram illustrating an example altitude separation between a first vehicle and a second vehicle. 
           [0074]      FIG. 4  is a chart depicting barometric pressure variation during an example first journey. 
           [0075]      FIG. 5  is a chart depicting barometric pressure variation during an example second journey. 
           [0076]      FIG. 6  is a block diagram illustrating a process flow for determining a sensor signal output. 
           [0077]      FIG. 7  is a block diagram of a system for generating altitude map data describing an altitude map for a geographic area. 
           [0078]      FIG. 8  is a block diagram of an example barometric pressure system. 
           [0079]      FIG. 9  is a chart depicting a specification of an example barometric pressure sensor included in the sensor set of the barometric pressure system. 
           [0080]      FIGS. 10A and 10B  are charts depicting example data that may be stored in a memory. 
           [0081]      FIG. 11  is a block diagram illustrating an example dedicated short range communication (DSRC) full position vector. 
           [0082]      FIG. 12  is a chart depicting a specification of an example capacitive humidity sensor included in the sensor set of the barometric pressure system. 
           [0083]      FIG. 13  is a chart depicting a specification of an example thermistor temperature sensor included in the sensor set of the barometric pressure system. 
           [0084]      FIG. 14  is a block diagram of an operating environment including a first vehicle and a second vehicle wirelessly communicating with one another via DSRC. 
           [0085]      FIG. 15  is a block diagram of an operating environment including a vehicle and a stationary roadside device wirelessly communicating with one another via DSRC. 
           [0086]      FIG. 16  is a block diagram of a system including a vehicle. 
       
    
    
     DETAILED DESCRIPTION 
       [0087]    A mobile computer atmospheric barometric pressure system (herein “the system” or “the barometric pressure system”) described according to some implementations. The barometric pressure system may be an element of a vehicle or a mobile device. 
         [0088]    The vehicle may include a special-purpose computing device. For example, the vehicle may include an onboard vehicle computer that includes hardware and software specially designed and manufactured to meet the needs of the onboard vehicle computer so that the vehicle provides a safe and desirable user experience that conforms to federal and local regulations (e.g., safety, air emissions, Federal Communication Commission regulation of wireless transmissions, etc.). In some implementations, the vehicle may include one or more onboard vehicle computers. 
         [0089]    The mobile device may include a processor-based computing device. For example, the mobile device may include a smartphone, tablet computer, laptop, smartwatch, Internet-of-Things device, personal computer, stationary roadside device, etc. The mobile device may include a processor. The processor may be programmed to provide some or all of the functionality described herein with reference to the barometric pressure system. In this way, the mobile device may be a special-purpose computing device programmed to provide the functionality described herein with reference to the barometric pressure system. In some implementations, the mobile device may be a smartphone of a driver traveling in a vehicle. 
         [0090]    The vehicle or the mobile device may include an alarm system. The alarm system may include a processor based computing device or be an element of a processor based computing device. For example, the alarm system may be an element of the onboard vehicle computer. The alarm system may also be an element of a smartphone or some other mobile device. 
         [0091]    The vehicle or mobile device may include a sensor set. The sensor set may include one or more electronic sensor devices. The electronic sensor devices of the sensor set may include electronic devices configured to record physical measurements of the environment of the alarm system. For example, the sensor set may include one or more barometric pressure sensors, one or more accelerometers, one or more humidity sensors, one or more temperature sensors, one or more cameras one or more roadway imaging devices, etc. The roadway imaging device may include one or more depth cameras. An example of a depth camera includes a light detection and ranging camera (a LIDAR camera). 
         [0092]    The alarm system may be communicatively coupled to the sensor set. For example, the alarm system may be an element of a vehicle and the alarm system and the sensor set may each be communicatively coupled to a bus, and the bus may be communicatively coupled to the onboard computer of the vehicle. In another example, the alarm system may be an element of a mobile client, the sensor set may be an element of a vehicle and the sensor set may be communicatively coupled to the mobile client via a wireless network such as Wi-Fi, Bluetooth™, Bluetooth LE™, or any other wireless communicative coupling. In yet another example, the alarm system and the sensor set are elements of the vehicle and the barometric pressure system is an element of the mobile client. The sensor set and the alarm system may be communicatively coupled to the onboard vehicle computer of the vehicle via a bus. The sensor set, alarm system or the onboard vehicle computer may be communicatively coupled to the mobile client via a wireless network such as Wi-Fi, Bluetooth™, Bluetooth LE™, or any other wireless communicative coupling. 
         [0093]    In some implementations, the alarm system is configured to analyze sensor data and determine whether the vehicle or the mobile device is on a trajectory that will result in a collision with an object on the roadway. The sensor data may include data describing measurements detected and recorded by one or more electronic sensor devices of the vehicle or the mobile device. The object may be another vehicle or any other object on the roadway. The alarm system is configured to provide a collision threat alarm to a driver of the vehicle or a user of the mobile device. The alarm system may provide the collision threat alarm if the vehicle or the mobile device is determined to be on a trajectory that will result in a collision. 
         [0094]    The collision threat alarm may include providing an audible signal to the driver (or the user), a visual signal to the driver (or the user) or a combination of an audible and visual signal to the driver (or the user). Proving the collision threat alarm to the driver (or the user) may be referred to as a collision threat alarm incident. 
         [0095]    The barometric pressure system may be configured to improve the performance or operation of the alarm system. For example, assume that the barometric pressure system is an element of a vehicle. The sensor set of the vehicle may include a global positioning system (GPS or GPS system), a speedometer, an accelerometer, a clock, etc. The sensor data may include data describing the location, speed and trajectory of the vehicle at a specified time. The sensor data may also include data describing the location, speed and trajectory of the object on the roadway. The sensor data may include motion data indicating the latitude and longitude coordinates of the vehicle and the object as indicated by one or more GPS systems of the vehicle or the object. The alarm system may analyze the sensor data and determine that a collision will occur between the vehicle and the object. However, the latitude and longitude data do not indicate the relative altitude of the vehicle and the object. If the vehicle is driving on a surface road and the object is driving on an overpass directly above the vehicle, the latitude and longitude data may indicate that the vehicle and the object are on a collision course with one another. In these situations the alarm system provides a collision threat alarm. However, this collision threat alarm is erroneous because the vehicle and the object are located at different altitudes, and so, the vehicle and the object will not collide with one another. The barometric pressure system described herein improves the performance of the alarm system by ensuring that such erroneous alarms do not occur. 
         [0096]    For example, the barometric pressure system may include a barometric pressure sensor to measure and record the barometric pressure for the vehicle. The barometric pressure indicates the altitude of the vehicle. Forces such as acceleration of the vehicle may cause the reading of the barometric pressure to be inaccurate. The barometric pressure system may include electronic sensor devices to record the acceleration or roadway noise. The barometric pressure system may include processors that are programmed to adjust the measured barometric pressure to account for these forces and achieve an accurate measurement of the barometric pressure. The adjusted measurement of the barometric pressure may be referred to herein as an “acceleration-adjusted reading of the barometric pressure,” an “acceleration-adjusted reading of the first barometric pressure,” an “acceleration-adjusted reading of the second barometric pressure” or some similar terminology. 
         [0097]    Other forces which may be measured and adjusted for include roadway noise. The roadway noise may include the noise and vibration caused by nearby vehicles that are passing the vehicle. For example, the roadway noise may include the noise and vibration caused in a smaller vehicle when a heavy truck passes the smaller vehicle. 
         [0098]    Other forces may be measured and accounted for when adjusting the data describing the reading of the barometric pressure. For example, the vehicle may include one or more windows. One or more of these windows may be open. An open window increases the wind inside the cabin of the vehicle, thereby changing the vehicle cabin and the measurements for sensors included in the vehicle. The amount of wind inside the vehicle may be related to (or proportional to) the number of open windows or the degree to which the one or more windows are open, and a corresponding increase in the vehicle cabin noise. Other vehicle ventilation systems (e.g., a vehicle air condition system, a vehicle sunroof or moonroof, etc.) also cause vehicle cabin noise. A processor of the barometric pressure system (or the onboard vehicle computer) may access the vehicle bus to retrieve one or more of the following: (1) action data describing commands to lower or raise vehicle windows, open or close a vehicle sunroof or moonroof, or turn on a vehicle air condition system or vehicle ventilation system; and (2) state data describing a degree to which a window is open, a degree to which a sunroof or moonroof is open, or a fan setting for a vehicle air condition system and whether the air condition system is configured to allow fresh air into the vehicle or recirculate the vehicle cabin air (recirculating vehicle cabin air corresponds to an increase in wind noise inside the vehicle cabin). The action data and the state data may be stored in a non-transitory memory of the vehicle that is communicatively coupled to the vehicle bus. The barometric pressure system may determine adjustments for the barometric pressure data based at least in part on one or more of the action data and the state data. For example, the barometric pressure system may use one or more noise models to adjust for the effect of the vehicle cabin noise on the measurements of the vehicle sensors (e.g., one or more barometric pressure sensors). 
         [0099]    Adjustments for noise caused by vehicle acceleration and ventilation is not performed by prior art barometric pressure systems. Moreover, the ability to determine accurate relative barometric pressure measurements and adjust the measurement based on vehicle acceleration and ventilation is beyond the ability of a human. For example, these relative barometric pressure measurements must be made and adjusted in real time or near real time (e.g., within one tenth of a second) in order to prevent a safety hazard. A human may require several minutes to make and adjust these relative barometric pressure measurements. Such human-based calculations would render the system inoperable because too much time would be required to enable the systems to determine whether alarm should be suppressed before vehicles either collided or drove past one another. Federal and state agencies will not allow such systems to be deployed because they would not meet minimum vehicle safety guidelines. Some embodiments of the barometric pressure system may not require wireless transmission of data among two or more objects. For example, the barometric pressure system may be an element of a mobile device. The mobile device may include a memory storing sensor data (e.g., barometric pressure data, location data describing the location of the mobile device, acceleration data describing the acceleration of the mobile device and inertia data describing the inertia of the mobile device), action data and state data. The barometric pressure data may be adjusted based on one or more of the acceleration data, the inertia data, the action data and the state data. 
         [0100]    Some embodiments of the barometric pressure system may not require wireless transmission of data among two or more objects. For example, the barometric pressure system may be an element of a mobile device. The mobile device may include a memory storing sensor data (e.g., barometric pressure data, location data describing the location of the mobile device, acceleration data describing the acceleration of the mobile device and inertia data describing the inertia of the mobile device), action data and state data. The barometric pressure data may be adjusted based on one or more of the acceleration data, the inertia data, the action data and the state data. 
       Example System Overview 
       [0101]      FIG. 1  is a block diagram illustrating an example operating environment  100  for providing the barometric pressure system  199  according to some implementations. In the illustrated embodiment, the environment  100  includes the following elements: a first vehicle  123 A; a second vehicle  123 B; a mobile device  198 ; and a server  155 . In the illustrated embodiment, these entities of the environment  100  may be communicatively coupled via a network  105 . The first vehicle  123 A and the second vehicle  123 B may be referred to individually as “the vehicle  123 ” or collectively as “the vehicles  123 .” 
         [0102]    While  FIG. 1  illustrates two vehicles  123 , one mobile device  198 , one server and one network, this disclosure may apply to an embodiment including three or more vehicles  123 , two or more mobile devices  193  and two or more servers  155 . Furthermore, although  FIG. 1  illustrates one network  105  coupled to the entities of the environment  100 , in practice one or more networks  105  may be connected to these entities. While  FIG. 1  includes one barometric pressure system  199  as an element of the first vehicle  123 A, in practice the environment  100  may include two or more barometric pressure systems  199 . For example, two or more of the first vehicle  123 A, the second vehicle  123 B and the mobile client  198  may include one or more barometric pressure systems  199 . 
         [0103]    The network  105  can be a conventional type, wired or wireless, and may have numerous different configurations including a star configuration, token ring configuration, or other configurations. Furthermore, the network  105  may include a local area network (LAN), a wide area network (WAN) (e.g., the Internet), or other interconnected data paths across which multiple devices may communicate. In some implementations, the network  105  may be a peer-to-peer network. The network  105  may also be coupled to or include portions of a telecommunications network for sending data in a variety of different communication protocols. In some implementations, the network  105  includes Bluetooth® communication networks or a cellular communications network for sending and receiving data via short messaging service (SMS), multimedia messaging service (MMS), hypertext transfer protocol (HTTP), direct data connection, WAP, e-mail, etc. In some implementations, the network  105  may include a GPS satellite for providing GPS navigation to the vehicle  123 . The network  105  may be a mobile data network such as 3G, 4G, LTE, Voice-over-LTE (“VoLTE”), DSRC, or any other mobile data network or combination of mobile data networks. 
         [0104]    The vehicle  123  may include an automobile, a bus, an airplane, a boat, or other vehicular conveyance. The vehicle  123  may be an electric vehicle or a hybrid vehicle. The vehicle  123  may include an internal combustion engine. The vehicle  123  may include a hydrogen fuel cell vehicle. In some implementations, the vehicle  123  may include an autonomous vehicle or a semi-autonomous vehicle  123 . In some implementations, the vehicle  123  may include a semi-autonomous vehicle  123  in which the vehicle  123  controls at least part of the steering functionality of the vehicle  123 . In the illustrated example, the first vehicle  123 A is communicatively coupled to the network  105  via signal line  118  and the second vehicle  123 B is communicatively coupled to the network  105  via signal line  164 . 
         [0105]    The vehicle  123  may include one or more of the following elements: an onboard vehicle computer  182 ; and a barometric pressure system  199 . The vehicle  123  may include other elements described below with reference to  FIG. 2A . 
         [0106]    The onboard vehicle computer  182  may include a non-transitory memory and a processor. The onboard vehicle computer  182  may include a special-purpose computing device. The onboard vehicle computer  182  may be communicatively coupled to the barometric pressure system  199 . 
         [0107]    The barometric pressure system  199  may include a computing device. The barometric pressure system  199  may include a non-transitory memory and a processor. The barometric pressure system  199  may include code and routines configured to provide the functionality described herein. For example, the code and routines of the barometric pressure system  199  may be stored on the non-transitory memory and executed by the processor. The processor of the barometric pressure system  199  may be programmed using the code and routines and configured to provide the functionality described herein. The barometric pressure system  199  will be described in more detail below with reference to  FIG. 2A . 
         [0108]    In some implementations, the barometric pressure system  199  may be implemented using hardware including a field-programmable gate array (“FPGA”) or an application-specific integrated circuit (“ASIC”). In some other implementations, the barometric pressure system  199  may be implemented using a combination of hardware and software. The barometric pressure system  199  may be stored in a combination of the devices and servers, or in one of the devices or servers. 
         [0109]    The server  155  may be a hardware server that includes a processor, a memory and network communication capabilities. The barometric pressure system  199  may transmit data to the server  155 . The barometric pressure system  199  may receive data from the server  155 . For example, the server  155  may aggregate barometric sensor data received from one or more barometric pressure systems  199 . The server  155  may include a mapping service. The mapping service may include code and routines configured to generate one or more maps describing the barometric pressure. 
         [0110]    For example, a fleet including a plurality of vehicles  123  may each include a barometric pressure system  199 . The barometric pressure systems  199  may transmit: (1) location data describing one or more locations; and (2) barometric pressure data describing the altitudes associated with the one or more locations described by the location data. The barometric pressure data may be adjusted to account for the acceleration or other forces affecting the measurement of the barometric pressure such as humidity or temperature. The server  155  may receive the data from the barometric pressure systems  199  and generate altitude map data describing an altitude map for a geographic area. The altitude map may include a plurality of locations included in the geographic area. The altitude map data may also describe a plurality of altitudes associated with the plurality of locations included in the geographic area. 
         [0111]    In some implementations, the barometric pressure system  199  of each vehicle  123  may communicate with other vehicles  123  via a network  105  such as DSRC and each barometric pressure system  199  may generate their own altitude map data. 
         [0112]    The server  155  may be communicatively coupled to the network  105  via a signal line  154 . 
         [0113]    The mobile device  198  may include a processor-based computing device. For example, the mobile device  198  may include a smartphone, tablet computer, laptop, smartwatch, Internet-of-Things device, personal computer, stationary roadside device, etc. The mobile device may include a barometric pressure system  199 . The mobile device  198  may include a processor. The processor may be programmed to provide some or all of the functionality described herein with reference to the barometric pressure system  199 . In this way, the mobile device  198  may be a special-purpose computing device programmed to provide the functionality described herein with reference to the barometric pressure system  199 . The mobile device  198  may be communicatively coupled to the network  105  via a signal line  158 . 
       Example Electronic Device 
       [0114]      FIG. 2A  is a block diagram illustrating an example barometric pressure system  200 . The barometric pressure system  200  may be an element of one or more of the vehicle  123  or the mobile device  198 . The barometric pressure system  200  is an embodiment of the barometric pressure system  199  described above with reference to  FIG. 1 . In some implementations, the barometric pressure system  200  may include a special-purpose computing device configured to provide some or all of the functionality described below with reference to the barometric pressure system  199 . 
         [0115]    The barometric pressure system  200  may include one or more of the following elements: the barometric pressure module  201 ; the calibration module  210 ; the onboard vehicle computer  182 ; the processor  225 ; the communication unit  245 ; the alarm system  250 ; the sensor set  252 ; the vehicle steering system  254 ; and the memory  227 . 
         [0116]    The onboard vehicle computer  182  was described above with reference to  FIG. 1 , and so, this description will not be repeated here. 
         [0117]    The calibration module  210  is communicatively coupled to the bus  220  via signal line  230 . The onboard vehicle computer  182  is communicatively coupled to the bus  220  via signal line  232 . The processor  225  is communicatively coupled to the bus  220  via signal line  234 . The memory  227  is communicatively coupled to the bus  220  via the signal line  236 . The communication unit  245  is communicatively coupled to the bus  220  via signal line  238 . The alarm system  250  is communicatively coupled to the bus  220  via signal line  240 . The sensor set  252  is communicatively coupled to the bus  220  via signal line  242 . The vehicle steering system  254  is communicatively coupled to the bus  220  via signal line  244 . In some implementations, one or more of the elements of the barometric pressure system  200  may share a signal line for communication with the bus  220 . 
         [0118]    The calibration module  210  may include code and routines configured to calibration one or more of the electronic sensor devices included in the sensor set  252 . For example, assume the barometric pressure system  200  is an element of a first vehicle  123 A. The barometric pressure system  200  may receive barometric pressure data from a second vehicle  123 B which is known to be located at substantially the same altitude as the first vehicle  123 A. The calibration module  210  may determine that the barometric pressure data recorded by the first vehicle  123 A describes a barometric pressure reading that is different from the barometric pressure reading received from the second vehicle. Over a period of time a pattern in the delta between the barometric pressure readings of the first vehicle  123 A and other devices may be observed by the calibration module  210 . The calibration module  210  may determine that one or more of the electronic sensor devices included the sensor set  252  will be calibrated based on the pattern. 
         [0119]    The calibration module  210  may determine that an electronic sensor device will be calibrated based on the quality data  297  stored in the memory  227 . The quality data  297  may describe time to live data or time since calibration data. For example, the calibration module  210  may determine that one or more of the electronic sensor devices included the sensor set  252  will be calibrated based on one or more of the following: (1) time to live data associated with the electronic sensor devices and describing an estimate of how long the plurality of electronic sensor devices are estimated to live; and (2) time since calibration data associated with the plurality of electronic sensor devices and describing how long since the plurality of electronic sensor devices was calibrated. 
         [0120]    In one embodiment, the calibration module  210  may provide the driver with a notification to service one or more of the electronic sensor devices of the sensor set  252 . For example, the calibration module  210  may provide a signal to the onboard vehicle computer  182  indicating that one or more of the electronic sensor devices may be calibrated. The onboard vehicle computer  182  may cause a light on the dash of the vehicle  123  to indicate that one or more of the electronic sensor devices may be calibrated. Optionally, the onboard vehicle computer  182  may cause an infotainment system of the vehicle  123  to provide an auditory, visual or audio-visual indication that that one or more of the electronic sensor devices may be calibrated. 
         [0121]    The processor  225  includes an arithmetic logic unit, a microprocessor, a general-purpose controller, or some other processor array to perform computations and provide electronic display signals to a display device. The processor  225  processes data signals and may include various computing architectures including a complex instruction set computer (CISC) architecture, a reduced instruction set computer (RISC) architecture, or an architecture implementing a combination of instruction sets. Although  FIG. 2A  includes a single processor  225 , multiple processors  225  may be included. The processor  225  may include a graphical processing unit. Other processors, operating systems, electronic sensor devices, displays, and physical configurations may be possible. 
         [0122]    The memory  227  is a tangible storage medium that stores instructions or data that may be accessed and executed by the processor  225 . The instructions or data may include code for performing the techniques described herein. The memory  227  may include a dynamic random access memory (DRAM) device, a static random access memory (SRAM) device, flash memory, or some other memory device. In some implementations, the memory  227  also includes a non-volatile memory or similar permanent storage device and media including a hard disk drive, a floppy disk drive, a CD-ROM device, a DVD-ROM device, a DVD-RAM device, a DVD-RW device, a flash memory device, or some other mass storage device for storing information on a more permanent basis. 
         [0123]    The communication unit  245  may include hardware that transmits and receives data to and from the network  105 . In some implementations, the communication unit  245  includes a port for direct physical connection to the network  105  or to another communication channel. For example, the communication unit  245  includes a USB, SD, CAT-5, or similar port for wired communication with the network  105 . In some implementations, the communication unit  245  includes a wireless transceiver for exchanging data with the network  105  or other communication channels using one or more wireless communication methods, including IEEE 802.11, IEEE 802.16, Bluetooth®, or another suitable wireless communication method. 
         [0124]    In some implementations, the communication unit  245  includes a cellular communications transceiver for sending and receiving data over a cellular communications network including via short messaging service (SMS), multimedia messaging service (MMS), hypertext transfer protocol (HTTP), direct data connection, WAP, e-mail, or another suitable type of electronic communication. In some implementations, the communication unit  245  includes a wired port and a wireless transceiver. The communication unit  245  also provides other conventional connections to the network  105  for distribution of files or media objects using standard network protocols including TCP/IP, HTTP, HTTPS, and SMTP, etc. The communication unit  245  may also provide connections to the network  105  for distribution of files, media objections or messages using the DSRC protocol. 
         [0125]    The alarm system  250  may include hardware and software for providing a collision threat alarm to a driver of a vehicle  123  or the user of a mobile device  198 . The alarm system  250  may include a processor based computing device or be an element of a processor based computing device. For example, the alarm system  250  may be an element of the onboard vehicle computer  182  or the barometric pressure system  200 . Optionally, the alarm system  250  may be an element of a smartphone or some other mobile device  198 . 
         [0126]    In some implementations, the alarm system  250  is configured to analyze data stored on the memory  227  and determine whether the vehicle  123  or the mobile device  198  is on a trajectory that will result in a collision with an object on the roadway. The data stored on the memory  227  may include data describing measurements detected and recorded by one or more electronic sensor devices of the sensor set  252 . The object may be another vehicle  123  or any other object on the roadway. The memory  227  may store, for example, action data and state data. 
         [0127]    The alarm system  250  is configured to provide a collision threat alarm to a driver of the vehicle  123  or a user of the mobile device  198 . The alarm system  250  may provide the collision threat alarm if the vehicle  123  or the mobile device  198  is determined by the alarm system  250  to be on a trajectory that will result in a collision. The collision threat alarm  250  may include providing an audible signal to the driver (or the user), a visual signal to the driver (or the user) or a combination of an audible and visual signal to the driver (or the user). Proving the collision threat alarm to the driver (or the user) may be referred to as a collision threat alarm incident. 
         [0128]    The barometric pressure system  200  may include code and routines configured to improve the performance or operation of the alarm system  250 . For example, assume that the barometric pressure system  200  is an element of a vehicle  123 . The data stored on the memory  227  may include data describing the location, speed and trajectory of the vehicle  123  at a specified time. The data stored on the memory  227  may also include data describing the location, speed and trajectory of the object on the roadway. The data stored on the memory  227  may include location data  284  indicating the latitude and longitude coordinates of the vehicle  123  and the object as indicated by one or more GPS systems (e.g., a GPS system of the vehicle  123  and a GPS system of the object). The alarm system  250  may analyze the data stored on the memory  227  and determine that a collision will occur between the vehicle  123  and the object. However, the latitude and longitude described by the location data  284  does not indicate the relative altitude of the vehicle  123  and the object. If the vehicle  123  is driving on a surface road and the object is driving on an overpass directly above the vehicle  123  and the surface road, the latitude and longitude described by the location data  284  may indicate that the vehicle  123  and the object are on a collision course with one another. In these situations, alarm systems  250  which are not improved by the barometric pressure system  200  will provide collision threat alarm. However, this collision threat alarm is erroneous because the vehicle  123  and the object are located at different altitudes, and so, the vehicle  123  and the object will not collide with one another. The barometric pressure system  200  described herein improves the performance of the alarm system  250  by ensuring that such erroneous alarms do not occur. 
         [0129]    For example, the sensor set  252  may include a barometric pressure sensor to measure and record the barometric pressure for the vehicle  123 . The barometric pressure may indicate the altitude of the vehicle  123 . Forces such as acceleration of the vehicle  123  may cause the reading of the barometric pressure recorded by the barometric pressure sensor to be inaccurate. The sensor set  252  may include one or more electronic sensor devices to record the acceleration of the vehicle  123  or roadway noise. The processor  225  may be programmed by the barometric pressure system  200  to adjust the measured barometric pressure to account for these forces and achieve an accurate measurement of the barometric pressure. The adjusted measurement of the barometric pressure may be referred to herein as an “acceleration-adjusted reading of the barometric pressure,” an “acceleration-adjusted reading of the first barometric pressure,” an “acceleration-adjusted reading of the second barometric pressure” or some similar terminology. 
         [0130]    The barometric pressure system  200  may also program the processor  225  to measure and adjust the barometric pressure data for roadway noise. The roadway noise may include the noise and vibration caused by nearby vehicles  123  that are passing the vehicle  123  which includes the barometric pressure system  200 . For example, the roadway noise may include the noise and vibration caused in a smaller vehicle when a heavy truck passes the smaller vehicle. 
         [0131]    The sensor set  252  may include one or more electronic sensor devices. The electronic sensor devices of the sensor set  252  may include electronic devices configured to record physical measurements of the environment of the alarm system  250 . For example, the sensor set  252  may include one or more barometric pressure sensors, one or more accelerometers, one or more humidity sensors, one or more temperature sensors, one or more cameras one or more roadway imaging devices, etc. The roadway imaging device may include one or more depth cameras. An example of a depth camera includes a light detection and ranging camera (a LIDAR camera). The data describing the measurements of the sensor set  252  may be referred to generally as “sensor data.” The memory  227  stores the sensor data. Data  280 ,  282 ,  284 ,  286 ,  288 ,  290  and  297  are examples of sensor data. 
         [0132]    The vehicle steering system  254  may include hardware, code and routines configured to steer a vehicle  123 . For example, the vehicle  123  may be an autonomous vehicle or a semi-autonomous vehicle. The vehicle steering system  254  may steer the vehicle based at least in part on the sensor data stored on the memory  227 . 
         [0133]    The memory  227  may store one of more of the following: environment data  280 ; altitude map data  282 ; location data  284 ; object data  286 ; trajectory data  288 ; motion data  290 ; quality data  297 ; and altitude separation data  298 . The memory  227  may also store action data and state data (not pictured). 
         [0134]    The environment data  280  may include data describing measurements of one or more physical attributes of the environment of the vehicle  123  or the mobile device  198 . The measurements may be recorded by one or more electronic sensor devices of the sensor set  252 . For example, the environment data  280  may describe one or more of the following: a barometric pressure measurement; a temperature measurement; an altitude estimate; a measurement of humidity; an adjusted estimate of the altitude based on the temperature, acceleration or humidity; one or more roadway images or image depth estimates for the one or more roadway images. The environment data  280  is described in more detail below with reference to  FIG. 2B . 
         [0135]    The altitude map data  282  may describe an altitude map. The altitude map described by the altitude map data  282  may include an altitude map for a geographic area and a plurality of altitudes associated with a plurality of locations included in the geographic area. For example, the altitude map may describe (1) one or more locations in the city of Los Altos Hills, Calif. and (2) one or more altitude estimates or barometric pressure readings associated with the one or more locations. 
         [0136]    The one or more locations may include any GPS coordinates, latitude and longitude coordinates, coordinates determined by wireless signal triangulation, etc. The one or more locations may include points of interest along a travel route provided by a navigation system. The one or more locations may include points of interest along a travel route for a commute. 
         [0137]    The points of interest may include one or more of the following: a business location; a traffic light; a stop sign; and geographical points where there is a statistically significant change in the barometric pressure measurement or altitude estimate. 
         [0138]    The location data  284  may describe the geographic location of the vehicle  123  or the mobile device  198 . For example, if the barometric pressure system  200  is an element of a vehicle  123 , then the location data  284  may describe the geographic location of the vehicle  123 . The location data  284  may be retrieved via the network  105 . The location data  284  may be stored in the memory  227  or provided to the communication module  202 . The sensor set  252  may include a GPS system. The GPS system may include hardware configured to provide satellite navigation. The GPS system may be an element of the communication unit  245 . 
         [0139]    The location data  284  may describe one or more of the following: the geographic location of the vehicle  123  or the mobile device  198 ; the time associated with the determination of the geographic location; and weather data describing the weather conditions (e.g., weather forecast, humidity, temperature) present at the geographic location for the current time. The geographic location may be described by Cartesian coordinates based on an origin present at the center of the earth. The geographic location may be the output of one or more global navigation satellite system (GNSS) positioning calculations. 
         [0140]    The object data  286  describes data received via the network  105 . For example, the object data  286  may include data transmitted by an object to the network  105 . The object may be a second vehicle  123  or a mobile client  198  (including a stationary roadside device). The object data  286  may describe a location, sensor data recorded by electronic sensor devices of the object and a timestamp associated with the location and the sensor data. The sensor data included in the object data  286  may include a barometric pressure measurement, a humidity measurement, a temperature measurement, an acceleration measurement, or a barometric pressure measurement that is adjusted for one or more of humidity, temperature and acceleration. 
         [0141]    The trajectory data  288  may describe the trajectory of the vehicle or the mobile device  198 . For example, the barometric pressure system  200  is an element of the vehicle  123 . The location data  284  may describe the location of the vehicle  123  at a given time. The vehicle may be traveling with at a determined velocity and acceleration (as described below with reference to the motion data  290 ). The trajectory data  288  may describe the trajectory of the vehicle  123 . The trajectory of the vehicle  123  or the mobile phone  198  may include the path followed by the vehicle of the mobile phone  198  under action of given forces such as velocity and acceleration. 
         [0142]    The motion data  290  may describe the physical motion of the vehicle  123  or the mobile device  198 . The motion data  290  may describe one or more physical forces applied to the vehicle  123  or the mobile device  198 . For example, the barometric pressure system  200  is an element of the vehicle  123 . The motion data  290  may include data describing one or more of the following: an axis of rotation of the vehicle  123 ; an acceleration of the vehicle  123 ; a velocity of the vehicle  123 ; a moment force applied to the vehicle  123 ; and any other measurable force applied to the vehicle  123 . 
         [0143]    The sensor set  252  may include any electronic sensor devices needed to measure the motion data  290 . For example, the sensor set  252  may include one or more of the following: a gyroscopic sensor, an accelerometer; a barometric pressure sensor; a torque sensor; a force transducer; a plate force sensor; an odometer; an impact sensor; a strain gauge; an angular position sensor; a rotary transformer and one or more slip rings; a tilt sensor; a velocity receiver; a shock detector and shock data logger; a synchro transducer; an integrated circuit piezocapacitve sensor; a gravimeter; an inclinometer; and a 6-axis force/moment sensor. 
         [0144]    The motion data  290  is described in more detail below with reference to  FIG. 2C . 
         [0145]    The quality data  297  may describe (1) the quality or state of one or more of the electronic sensor devices included in the sensor set  252  or (2) the quality or state of the sensor data. 
         [0146]    The quality data  297  may also describe a delta between an altitude estimate determined by the barometric pressure system  200  and an altitude determined by some other electronic device. For example, assume the barometric pressure system  200  is an element of a first vehicle  123 A. The barometric pressure system  200  may receive barometric pressure data from a second vehicle  123 B which is known to be located at substantially the same altitude as the first vehicle  123 A. The calibration module  210  may determine that the barometric pressure data recorded by the first vehicle  123 A describes a barometric pressure reading that is different from the barometric pressure reading received from the second vehicle  123 B. The calibration module  210  may store quality data  297  in the memory  227  describing the delta between the barometric pressure data recorded by the first vehicle  123 A and the barometric pressure reading received from the second vehicle  123 B. The calibration module  210  may repeat this process for other combinations of barometric pressure data. Over a period of time a pattern in the delta between the barometric pressure readings of the first vehicle  123 A and other devices may be observed or determined by the calibration module  210 . The calibration module  210  may determine that one or more of the electronic sensor devices included the sensor set  252  will be calibrated based on the pattern. For example, if the average delta is some positive value indicated by “X,” then the barometric pressure data recorded by the barometric pressure system will be increased by “X” to account for the pattern in the delta. Optionally, the value of “X” may be used by the calibration module  210  to electronically calibrate one or more of the barometric pressure sensors included in the sensor set  252 . 
         [0147]    In some implementations, the calibration module  210  may also apply Winsorising outlier filtering techniques to determine the value of “X” used to adjust the barometric pressure data so that statistically significant outliers do not affect the value of “X.” 
         [0148]    In some implementations, the quality data  297  may include time to live data or time since calibration data. Optionally, each instance of the time to live data or the time since calibration data may be associated with a particular electronic sensor device. One or more instances of the time to live data or the time since calibration data may be included in the quality data  297 . 
         [0149]    The time to live data may describe, for a given electronic sensor device included in the sensor set  252 , an estimate of how long the electronic sensor device  252  is estimated to live. For example, the electronic sensor device may have a known or estimated life cycle. The service time for the electronic sensor device may be tracked and known. The service time may describe how much time the electronic sensor device has been in service. The service time may be included in the time to live data. The time to live data may be determined by subtracting the estimated life cycle of the electronic sensor device from the service time for the electronic sensor device. 
         [0150]    The time since calibration data may describe, for a given electronic sensor device, how long since the electronic sensor device was calibrated. The time since calibration data may also describe how frequently the electronic sensor device is calibrated according to the specification for the electronic sensor device. If the time since calibration exceeds the frequency indicated by the specification, then the calibration module  210  determines to calibrate the electronic sensor device. 
         [0151]    The altitude separation data  298  describes an altitude separation for two objects. The altitude separation includes a difference in the altitude of two objects. For example, assume that a first vehicle  123 A is traveling on a roadway having an altitude of “X” and a second vehicle  123 B is traveling on a roadway having an altitude of “Y.” Further assume that “Y” is greater than “X.” The altitude separation data  298  describes the difference in altitude for the first vehicle  123 A and the second vehicle  123 B. In this example, the altitude separation is the difference between “Y” and “X” (e.g., Y−X=altitude separation). An example of altitude separation is described below with reference to  FIG. 3 . 
         [0152]    The altitude separation data  298  is determined by the analysis module  208  based on differential barometric pressure data (not pictured) stored in the memory  227 . The differential barometric pressure data may describe a differential barometric pressure for two objects. For example, the barometric pressure system  200  is an element of a first vehicle  123 A. The environment data  280  may include first barometric pressure data describing the barometric pressure measured in a column of air above the first vehicle  123 A. The object data  286  may include second barometric pressure data describing the barometric pressure measured in a column of air above a second vehicle  123 B. The analysis module  208  may include code and routines configured to determine the differential barometric pressure. For example, the differential barometric pressure for the first vehicle  123 A and the second vehicle  123 B is determined by subtracting (1) the lesser of the first barometric pressure data and the second barometric pressure data from (2) the greater of the first barometric pressure data and the second barometric pressure data. 
         [0153]    The analysis module  208  may include code and routines configured to determine an estimate of the altitude separation between two objects based on the differential barometric pressure data. The memory  227  may include a data structure used by the analysis module  208  to determine the altitude separation estimate for two objects based on the differential barometric pressure for these two objects. For example, assuming a temperature of 60 degrees Fahrenheit, our experimentation has shown each 1 millibar unit of differential barometric pressure at sea level corresponds to an estimated altitude separation of 27.4 feet. The analysis module  208  may determine that a differential barometric pressure of 3 millibars at 60 degrees Fahrenheit corresponds to an altitude separation of 82.2 feet (27.4 feet/millibar multiplied by 3 millibars). 
         [0154]    The memory  227  may include other data used to determine an estimate of the altitude separation between two objects based on the differential barometric pressure data. For example, assuming a temperature of 20 degrees Fahrenheit, our experimentation has shown that each 1 millibar unit of differential barometric pressure at sea level corresponds to an estimated altitude separation of 25 feet. In another example, assuming a temperature of 60 degrees Fahrenheit, our experimentation has shown that each 1 millibar unit of differential barometric pressure at 7,000 feet above sea level corresponds to an estimated altitude separation of 33 feet.  FIGS. 10A and 10B  include data that may be stored in the memory  227  and used by the analysis module  208  to convert differential barometric pressure to altitude separation estimates. 
         [0155]    In some implementations, the memory  227  may store a lookup table describing acceptable differential barometric pressures. For example, the analysis module  208  may determine the differential barometric pressure for two objects. The analysis module  208  may query the lookup table stored in the memory  227 . If the query returns a non-empty result or a result other than null, then the analysis module  208  may determine that the estimated altitude separation is greater than zero. The analysis module  208  may determine that an estimated altitude separation greater than zero corresponds to suppression of a collision threat alarm since the two objects are not at the same altitude. 
         [0156]    Differential barometric pressure is described in more detail below with reference to  FIG. 3 . 
         [0157]    In some implementations, the memory  227  may store a distance coefficient. The analysis module  208  may apply the distance coefficient to the differential barometric pressure to determine the estimated altitude separation between the two objects. The distance coefficient may be configured to account for a worst case or typical scenario. For example, distance coefficient may be selected by the analysis module  208  from a range of 25 to 33 separation feet per millibar of differential barometric pressure. The analysis module  208  may select the distance coefficient based on sensor data or other factors applicable to the present use case scenario. For example, the analysis module may select a distance coefficient of 25 separation feet per millibar based on the sensor data including acceleration of one or more of the objects. The differential barometric pressure between the two objects may be 2 millibar. The analysis module  208  may determine that the estimated altitude separation is 50 feet (2 millibar multiplied by 25 separation feet per millibar). The analysis module  208  is described in more detail below with reference to the barometric pressure module  201 . 
         [0158]    In some implementations, the barometric pressure module  201  may include code and routines that are stored on the memory  227 . In some implementations, the processor  225  may be programmed by the code and routines of the barometric pressure module  201 . In some implementations, the code and routines of the barometric pressure module  201  may be stored in an on chip memory of the processor  225 . 
         [0159]    In some implementations, the barometric pressure module  201  includes one or more of the following elements: a communication module  202 ; a sensor module  204 ; an object-to-object communication module  206 ; and an analysis module  208 . 
         [0160]    The communication module  202  is communicatively coupled to the bus  220  via signal line  222 . The sensor module  204  is communicatively coupled to the bus  220  via signal line  224 . The object-to-object communication module  206  is communicatively coupled to the bus  220  via signal line  226 . The analysis module  208  is communicatively coupled to the bus  220  via signal line  228 . The bus  220  may include a vehicle bus. 
         [0161]    The communication module  202  may include code and routines configured to handle communications between the application assurance system  199  and other components of the barometric pressure system  200 . In some implementations, the communication module  202  can include a set of instructions executable by the processor  225  to provide the functionality described below for handling communications between the application assurance system  199  and other components of the barometric pressure system  200 . In some implementations, the communication module  202  can be stored in the memory  227  of the barometric pressure system  200  and can be accessible and executable by the processor  225 . 
         [0162]    The communication module  202  sends and receives data, via the communication unit  245 , to and from the network  105 . For example, the communication module  202  receives, via the communication unit  245 , location data  284  or object data  286  from the network  105 . 
         [0163]    In some implementations, the communication module  202  receives data from components of the barometric pressure system  200  and stores the data in the memory  227 . 
         [0164]    The sensor module  204  may include code and routines configured to cause one or more of the electronic sensor devices to measure one or more physical attributes and store sensor data in the memory  227 . 
         [0165]    The object-to-object communication module  206  may include code and routines configured to manage object-to-object communications for the barometric pressure system  200 . For example, the object-to-object communication module  206  manages DSRC communications among two or more objects. The objects may include one or more of the following: a vehicle  123  or a mobile device  198  (including a stationary roadside device). The object-to-object communication module  206  may build a DSRC message to be transmitted by the communication unit  245  to an object. An example of a DSRC message is described below with reference to  FIG. 11 . The object-to-object communication module  206  may analyze received messages to determine their content. The object-to-object communication module  206  may store data included in received messages in the memory  227  as object data  286 . 
         [0166]    The analysis module  208  may include code and routines for analyzing the data stored in the memory  227  and making determinations based on the analysis. The determinations of the analysis module  208  may be configured to improve the performance of the alarm system  250 . 
         [0167]    The analysis module  208  may be described with reference to an object, a vehicle  123 , a first vehicle  123 A, a second vehicle  123 B, a mobile device  198 ; a first mobile device  198  and a second mobile device  198 . In some implementations, the description of the analysis module  208  may refer to systems including a plurality of barometric pressure systems  200 . For example, the analysis module  208  may be described with reference to a system that includes one or more objects, vehicles  123  or mobile devices  198  and one or more of these devices may include their own barometric pressure system  200 . When describing the analysis module  208 , the description may use the reference characters of  FIG. 2A  while using the words “first” and “second” to remove ambiguity about whether elements are components of the first vehicle  123 A or the second vehicle  123 B. For example, the first vehicle  123 A may include a “first onboard vehicle computer  182 ” and the second vehicle  123 B may include a “second onboard vehicle computer  182 .” Similarly, the analysis module  208  may be described with reference to a system including multiple mobile devices  198 , and these may be referred to as “a first mobile device  198 ,” “a second mobile device  198 ” and etc. Example implementations of the analysis module  208  will now be described. 
         [0168]    In some implementations, the determinations of the analysis module  208  may be configured to suppress an erroneous collision threat alarm. For example, the analysis module  208  may include code and routines configured to estimate an altitude separation for two or more objects. The analysis module  208  may include code and routines configured to suppress a collision threat alarm of the alarm system  250  based on the estimate of altitude separation. 
         [0169]    For example, assume that the barometric pressure system  200  is an element of a vehicle  123 . The sensor data may include data describing the location, speed and trajectory of the vehicle  123  at a specified time. The sensor data may also include data describing the location, speed and trajectory of an object on the roadway. The sensor data may include location data indicating the latitude and longitude coordinates of the vehicle  123  and the object as indicated by one or more GPS systems. The alarm system  260  may analyze the sensor data and determine that a collision will occur between the vehicle and the object. However, the latitude and longitude data do not indicate the relative altitude of the vehicle and the object. If the vehicle  123  is driving on a surface road and the object is driving on an overpass directly above the vehicle  123  and the surface road (so that the overpass is at a higher altitude), the latitude and longitude data may indicate that the vehicle  123  and the object are on a collision course with one another. In these situations the alarm system  250  provides a collision threat alarm. However, this collision threat alarm is erroneous because the vehicle  123  and the object are located at different altitudes, and so, the vehicle  123  and the object will not collide with one another. 
         [0170]    The alarm system  250  may provide a signal to the communication module  202  indicating the potential collision threat alarm incident. The communication module  202  may provide the signal to the analysis module  208 . The analysis module  208  may include code and routines configured to perform one or more of the following steps responsive to receipt of the signal indicating the potential collision threat alarm: (1) analyze the sensor data stored on the memory  227 ; (2) determine an estimate of the altitude separation between the vehicle  123  and the object based on the sensor data; (3) store altitude separation estimate data  298  in the memory  227  describing the altitude separation; (5) determine that the potential vehicle threat alarm would be erroneous based on the altitude separation data  298  indicating that the vehicle and the object are at different altitudes; and (6) suppress the collision threat alarm so that the alarm system  250  does not provide the collision threat alarm to the driver. In this way, the barometric pressure system  200  described herein improves the performance of the alarm system  260  by ensuring that such erroneous alarms do not occur. 
         [0171]    For example, the sensor set  252  of the barometric pressure system  200  may include one or more barometric pressure sensors to measure and record the barometric pressure for the vehicle  123 . The barometric pressure indicates the altitude of the vehicle. Forces such as acceleration of the vehicle may cause the reading of the barometric pressure to be inaccurate. The sensor set  252  of the barometric pressure system  200  may include one or more electronic sensor devices to record the acceleration (e.g., an accelerometer). The analysis module  208  may include code and routines configured to adjust the measured barometric pressure described by the barometric pressure data to account for acceleration to achieve a more accurate measurement of the barometric pressure versus not accounting for these forces. The adjusted measurement of the barometric pressure may be referred to herein as an “acceleration-adjusted reading of the barometric pressure,” an “acceleration-adjusted reading of the first barometric pressure,” an “acceleration-adjusted reading of the second barometric pressure” or some similar terminology based on the forces used to adjust the barometric pressure data. In one embodiment, the processor  225  is programmed by the code and routines of the analysis module  208  to determine the acceleration-adjusted barometric pressure based on the sensor data stored in the memory  227 . 
         [0172]    The analysis module  208  may include code and routines configured to account for other forces such as roadway noise. The roadway noise may include the noise and vibration caused by nearby vehicles that are passing the vehicle. For example, the roadway noise may include the noise and vibration caused in a smaller vehicle  123  when a heavy truck passes the smaller vehicle  123 . 
         [0173]    In some implementations, the barometric pressure system  200  includes a dedicated short range communication network (DSRC communication network). The barometric pressure system  200  may be an element of a first vehicle  123 A. The first vehicle  123 A may be communicatively coupled to a second vehicle  123 B via the DSRC communication network. The second vehicle  123 B may be traveling on a roadway in the same direction as the first vehicle  123 A. The second vehicle  123 B may be located in a different lane relative to the first vehicle  123 A while still traveling in the same direction as the first vehicle  123 A. For example, the first vehicle  123 A may be located in the first lane or a northbound roadway. The second vehicle  123 B may be located in the second lane of the same northbound roadway. 
         [0174]    The first vehicle  123 A and the second vehicle  123 B may separately include some or all of the elements of the barometric pressure system  200  depicted in  FIG. 2A . 
         [0175]    The first vehicle  123 A may include a set of first electronic sensor devices, a second electronic sensor device and a first onboard vehicle computer  182 . The first electronic sensor devices may include a plurality of barometric pressure sensors configured to measure the barometric pressure and store the measurement in the memory  227  as barometric pressure data. The second electronic sensor device may include an accelerometer, an odometer or some other electronic sensor device configured to record the acceleration of the first vehicle  123 A. 
         [0176]    The second vehicle  123 B may include an alarm system  250 . The alarm system  250  may configured to analyze sensor data of the second vehicle  123 B and determine whether the second vehicle  123 B is on a trajectory that will result in the second vehicle  123 B colliding with an object on the roadway. The object may be another vehicle (e.g., the first vehicle  123 A) or any other object on the roadway. The alarm system  250  may be configured to provide a collision threat alarm to a driver of the second vehicle  123 B if the second vehicle  123 B is determined by the alarm system  250  to be on a trajectory that will result in the second vehicle  123 B colliding with an object on the roadway. 
         [0177]    The set of first electronic sensor devices of the first vehicle  123 A may be configured to record first barometric pressure data describing a first barometric pressure associated with the first vehicle  123 A. The first barometric pressure data may be stored in the memory  227  of the barometric pressure system  200 . The second electronic sensor device of the first vehicle  123 A may be configured to record acceleration data describing an acceleration of the first vehicle  123 A. The acceleration data may be stored in the memory  227  of the barometric pressure system  200 . 
         [0178]    The first onboard vehicle computer  182  of the first vehicle  123 A may be communicatively coupled to the DSRC communication network, the set of first electronic sensor devices and the second electronic sensor device. The first onboard vehicle computer  182  may be programmed by a first analysis module  208  of the first vehicle  123 A to (1) adjust the first barometric pressure data based on the acceleration of the first vehicle  123 A so that the first barometric pressure data describes an acceleration-adjusted reading of the first barometric pressure associated with the first vehicle  123 A and (2) automatically transmit the first barometric pressure data describing the acceleration-adjusted reading to a selected channel of the DSRC communication network  182 . 
         [0179]    The second vehicle  123 B may include a second onboard vehicle computer  182 . The second onboard vehicle computer  182  is communicatively coupled to the selected channel of the DSRC communication network. The second onboard vehicle computer  182  is programmed by a second analysis module  208  of the second vehicle  123 B to receive the first barometric pressure data describing the acceleration-adjusted reading. The second onboard vehicle computer  182  is programmed by the second analysis module  208  of the second vehicle  123 B to determine an estimate of altitude separation based on the first barometric pressure data and second barometric pressure data describing a second barometric pressure associated with the second vehicle  123 B. 
         [0180]    The estimate of altitude separation may describe an estimate of whether the first vehicle  123 A and the second vehicle  123 B are located at substantially the same altitude. The second onboard vehicle computer  182  of the second vehicle  123 B is programmed by the second analysis module  208  to suppress a collision threat alarm based on the estimate of altitude separation indicating that the first vehicle  123 A and the second vehicle  123 B are not located at substantially the same altitude. 
         [0181]    In some implementations, the barometric pressure system  200  is an element of a mobile device  198 . The barometric pressure system  200  may include: a network  105  communicatively coupled to the mobile device  198 ; a first electronic sensor device configured to record barometric pressure data describing a barometric pressure associated with the mobile device  198 ; a second electronic sensor device configured to record acceleration data describing an acceleration of the mobile device  198 ; and a processor  225  communicatively coupled to the network  106 , the first electronic sensor device and the second electronic sensor device. 
         [0182]    The processor  225  may be programmed by the analysis module  208  to adjust the barometric pressure data based on the acceleration of the mobile device  198  so that the barometric pressure data describes an acceleration-adjusted reading of the barometric pressure associated with the mobile device  198 . The processor  225  may also be programmed by the analysis module  208  to automatically transmit the barometric pressure data describing the acceleration-adjusted reading to the network  105 . The processor  225  may also be programmed by the analysis module  208  to transmit the barometric pressure data to the network  105  in substantially real time. For example, the processor  225  may be programmed to transmit the barometric pressure data to the network every 0.1 seconds. In some implementations, the processor  225  may also be programmed by the analysis module  208  to transmit the barometric pressure data to the network  105  at an interval configured by the processor  225  to avoid a collision threat alarm incident. 
         [0183]    In some implementations, the barometric pressure system  200  is an element of a mobile device  198  including a network  105  communicatively coupled to the mobile device  198 . The barometric pressure system  200  may include a set of first electronic sensor devices configured to record barometric pressure data describing a barometric pressure associated with the mobile device  198 . The barometric pressure system  200  may include a second electronic sensor device configured to record acceleration data describing an acceleration of the mobile device  198 . The barometric pressure system  200  may also include a processor  225  communicatively coupled to the network  105 , the set of first electronic sensor devices and the second electronic sensor device. 
         [0184]    The analysis module  208  of the barometric pressure system  200  may include code and routines configured to (1) determine quality data  297  describing a quality of the barometric pressure data and (2) adjust the barometric pressure data based on the quality of the barometric pressure data and the acceleration of the mobile device  198  so that the barometric pressure data describes a quality and acceleration-adjusted reading of the barometric pressure associated with the mobile device  198 . The analysis module  208  may also include code and routines configured to automatically transmit the barometric pressure data describing the acceleration-adjusted reading to the network  105 . 
         [0185]    The processor  225  may be programmed by the analysis module  208  to (1) determine quality data describing a quality of the barometric pressure data and (2) adjust the barometric pressure data based on the quality of the barometric pressure data and the acceleration of the mobile device  198  so that the barometric pressure data describes a quality and acceleration-adjusted reading of the barometric pressure associated with the mobile device  198 . The processor  225  is also programmed by the analysis module  208  to automatically transmit the barometric pressure data describing the acceleration-adjusted reading to the network  105 . 
         [0186]    In some implementations, the quality data  297  may be based on one or more of (1) time to live data associated with the set of first electronic sensor devices and describing an estimate of how long the set of first electronic sensor devices are estimated to live and (2) time since calibration data associated with the set of first electronic sensor devices and describing how long since the set of first electronic sensor devices was calibrated. 
         [0187]    In some implementations, the barometric pressure system  200  may comprise a network  105  communicatively coupled to a first mobile device  198  and a second mobile device  198 . The first mobile device  198  and the second mobile device  198  may each include a barometric pressure system  200 . 
         [0188]    The first mobile device  198  may include a set of first electronic sensor devices, a second electronic sensor device and a first processor  225 . The set of first electronic sensor devices may be configured to record first barometric pressure data describing a first barometric pressure associated with the first mobile device  198 . The second electronic sensor device may be configured to record acceleration data describing an acceleration of the first mobile device  198 . 
         [0189]    The first processor  225  may be communicatively coupled to the network  105 , the set of first electronic sensor devices and the second electronic sensor device. The first processor  225  may be programmed by a first analysis module  208  to (1) adjust the first barometric pressure data based on the acceleration of the first mobile device  198  so that the first barometric pressure data describes an acceleration-adjusted reading of the first barometric pressure associated with the first mobile device  198  and (2) automatically transmit the first barometric pressure data describing the acceleration-adjusted reading to the network  105 . 
         [0190]    The second mobile device  198  may be communicatively coupled to the network  105  and configured to receive the first barometric pressure data describing the acceleration-adjusted reading from the network  105 . A second processor  225  of the second mobile device  198  may be programmed by a second analysis module  208  to determine altitude separation estimate data  298  based on the first barometric pressure data and second barometric pressure data describing a second barometric pressure associated with the second mobile device  198 . The altitude separation estimate data  298  may describe an estimate of whether the first mobile device  198  and the second mobile device  198  are located at substantially the same altitude. In some implementations, the altitude separation estimate data  298  may describe a delta in altitude for the first mobile device  198  and the second mobile device  198 . In some implementations, at least one of the first mobile device  198  and the second mobile device  198  is a vehicle  123 . 
         [0191]    In some implementations, the first analysis module  208  of the first mobile device  198  may include code and routines configured to determine a first geographic location vector based on sensor data stored in the first memory  227  of the first mobile device  198 . For example, the first analysis module  208  of the first mobile device  198  may determines the first geographic location vector based on (1) a first location of the first mobile device  198  at a first time, (2) a first speed (or velocity) of the first mobile device  198 , (3) and a first direction of the first mobile device  198  and (4) the first barometric pressure data describing the acceleration-adjusted reading. The first geographic location vector may include vector data describing the location of the first mobile device  198  (e.g., the first location) at a first time (e.g., a specified time), the speed of the first mobile device  198 , the direction of travel of the first mobile device  198  and the acceleration-adjusted reading of the barometric pressure associated with the first mobile device  198  while present at the location or substantially at the first location. The first mobile device  198  transmits the first geographical location vector to the network  105 . 
         [0192]    The second mobile device  198  may receive the first geographical location vector from the network  105 . The second analysis module  208  of the second mobile device  198  may include code and routines configured to determine a second geographic location vector based on sensor data stored in the first memory  227  of the first mobile device  198 . For example, the second analysis module  208  may determine the second geographic location vector based on (1) a second location of the second mobile device  198  at a second time, (2) a second speed of the second mobile device  198 ; (3) a second direction of the second mobile device  198 ; and (4) the second barometric pressure data associated with the second mobile device  198 . 
         [0193]    The second processor  225  of the second mobile device  198  may be programmed by the second analysis module  208  to determine a second geographic location vector based on (1) a second location of the second mobile device at a second time, (2) a second speed of the second mobile device; (3) a second direction of the second mobile device  198 ; and (4) the second barometric pressure data associated with the second mobile device  198 . 
         [0194]    The second geographic location vector may include vector data describing the location of the second mobile device  198  (e.g., the second location) at a second time (e.g., a specified time), the speed of the second mobile device  198 , the direction of travel of the second mobile device  198  and the acceleration-adjusted reading of the barometric pressure associated with the second mobile device  198  while present at the location or substantially at the second location. 
         [0195]    The second analysis module  208  may also include code and routines configured to determine an estimate of whether the first mobile device  198  and the second mobile device  198  will collide based on the first geographical location vector, the second geographical location vector and the estimate of altitude separation. The second processor  225  may be programmed by the second analysis module  208  to determine an estimate of whether the first mobile device  198  and the second mobile device  198  will collide based on the first geographical location vector, the second geographical location vector and the estimate of altitude separation. 
         [0196]    In some implementations, the first geographical location vector and the second geographical location vector may indicate that the first mobile device  198  and the second mobile device  198  will collide but the second processor  225  of the second mobile device  198  determines that the first mobile device  198  and the second mobile device  198  will not collide based on a determination that the estimate of altitude separation indicates that the first mobile device  198  and the second mobile device  198  are not located at substantially the same altitude. 
         [0197]    In some implementations, the second processor  225  of the second mobile device  198  suppresses a collision threat alarm based on a determination that the first mobile device  198  and the second mobile device  198  will not collide because they are not located at substantially the same altitude. 
         [0198]    In some implementations, the barometric pressure system  200  is an element of a vehicle  123 . The barometric pressure system  200  may include a plurality of electronic sensor devices configured to record first barometric pressure data describing a first barometric pressure associated with the vehicle  123 . Each of the electronic sensor devices records a separate barometric pressure reading associated with the vehicle  123 . 
         [0199]    The analysis module  208  of the barometric pressure system  200  may include code and routines configured to (1) analyze the separate barometric pressure readings associated with the plurality of electronic sensor devices to determine, for each of the electronic sensor devices, a confidence factor indicating confidence in the accuracy of the barometric pressure reading for each of the electronic sensor devices and (2) determine whether to provide a sensor service recommendation based on the confidence factor. In some implementations, analysis module  208  may include code and routines configured to analyze variation of the separate barometric pressure readings among the plurality of electronic sensor devices to determine the confidence factor. 
         [0200]    The barometric pressure system  200  of the vehicle  123  may also include an onboard vehicle computer  182  that is communicatively coupled to the plurality of electronic sensor devices. The onboard vehicle computer  182  may be programmed by the analysis module  208  to (1) analyze the separate barometric pressure readings associated with the plurality of electronic sensor devices to determine, for each of the electronic sensor devices, a confidence factor indicating confidence in the accuracy of the barometric pressure reading for each of the electronic sensor devices and (2) determine whether to provide a sensor service recommendation based on the confidence factor. 
         [0201]    In some implementations, the onboard vehicle computer  182  may be programmed by the analysis module  208  to analyze variation of the separate barometric pressure readings among the plurality of electronic sensor devices to determine the confidence factor. In some implementations, the confidence factor may be based in part on one or more of (1) time to live data associated with the plurality of electronic sensor devices and describing an estimate of how long the plurality of electronic sensor devices are estimated to live and (2) time since calibration data associated with the plurality of electronic sensor devices and describing how long since the plurality of electronic sensor devices was calibrated. 
         [0202]    In some implementations, the barometric pressure system  200  also includes a network  105  and a mobile device  195 . The vehicle  123  and the mobile device  198  may be communicatively coupled to the network  105 . The mobile device  198  may include functionality to determine a barometric pressure reading for the mobile device  198 . For example, the mobile device  198  may include a second barometric pressure system  200 . The vehicle  123  may receive second barometric pressure data describing a second barometric pressure reading associated with the mobile device  198 . For example, the communication unit  245  of the vehicle  123  may receive the second barometric pressure data from the network  105 . 
         [0203]    The onboard vehicle computer  182  may be programmed by the analysis module  208  to (1) analyze the second barometric pressure reading associated with the mobile device and the separate barometric pressure readings associated with the plurality of electronic sensor devices to determine, for each of the electronic sensor devices, the confidence factor indicating confidence in the accuracy of the barometric pressure reading for each of the electronic sensor devices and (2) determine whether to provide the sensor service recommendation based on the confidence factor. 
         [0204]    The second mobile device  198  may be communicatively coupled to the network  105 . The second mobile device  198  may be configured to receive the first barometric pressure data describing the acceleration-adjusted reading and determine an estimate of altitude separation based on the first barometric pressure data and second barometric pressure data describing a second barometric pressure associated with the second mobile device  198 . The estimate of altitude separation may describe an estimate of whether the first mobile device  198  and the second mobile device  198  are located at substantially the same altitude. 
         [0205]    In some implementations, the barometric pressure system  200  is an element of a mobile device  198 . The analysis module  208  of the barometric system  200  may include code and routines configured to determine the location of the mobile device  198  based on an acceleration-adjusted barometric pressure. The barometric pressure system  200  may include a memory  227  storing altitude map data  282 . The altitude map data  282  may describe an altitude map for a geographic area and a plurality of altitudes associated with a plurality of locations included in the geographic area. The barometric pressure system  200  may also include a GPS system configured to determine location data  284  describing an estimate of a location of the mobile device  198 . The barometric pressure system  200  may also include a set of first electronic sensor devices configured to record barometric pressure data describing a barometric pressure associated with the mobile device  198 . The barometric pressure system  200  may also include a second electronic sensor device configured to record acceleration data describing an acceleration of the mobile device  198 . 
         [0206]    The analysis module  208  of the barometric pressure system  200  may include code and routines configured to (1) adjust the barometric pressure data based on the acceleration of the mobile device  198  so that the barometric pressure data describes an acceleration-adjusted reading of the barometric pressure associated with the mobile device  198 , (2) determine an altitude-based geographic location of the mobile device  198  by analyzing the altitude map to identify a location having an altitude indicated by the barometric pressure data and (3) adjust the location data based on the altitude-based geographic location so that the location data more accurately describes the location of the mobile device  198 . In this way, the barometric pressure system  200  may in some implementations be configured to improve the accuracy of a GPS system by increasing the accuracy of the GPS system. 
         [0207]    The barometric pressure system  200  may also include a processor  225  communicatively coupled to the memory  227 , the GPS system, the set of first electronic sensor devices and the second electronic sensor device. The processor  225  may be programmed by the analysis module  208  to (1) adjust the barometric pressure data based on the acceleration of the mobile device  198  so that the barometric pressure data describes an acceleration-adjusted reading of the barometric pressure associated with the mobile device  198 , (2) determine an altitude-based geographic location of the mobile device  198  by analyzing the altitude map to identify a location having an altitude indicated by the barometric pressure data and (3) adjust the location data based on the altitude-based geographic location so that the location data more accurately describes the location of the mobile device  198 . 
         [0208]    In some implementations, the barometric pressure system  200  is an element of a vehicle  123  and the analysis module  208  includes code and routines configured to automatically generate an altitude map for a lane of a roadway in a geographic area based on an acceleration-adjusted barometric pressure. The barometric pressure system  200  may include a GPS system configured to determine location data  284  describing an estimate of a location of the vehicle  123 . The barometric pressure system  200  may also include a roadway imaging device configured to determine which lane the vehicle is located in while at the location. The roadway imaging device may include a LIDAR camera or some other imaging device (e.g., a non-high definition camera, a high definition camera, etc.). The barometric pressure system  200  may also include a set of first electronic sensor devices configured to record barometric pressure data describing a barometric pressure associated with the vehicle  123 . The barometric pressure system may also include a second electronic sensor device configured to record acceleration data describing an acceleration of the vehicle  123 . 
         [0209]    The analysis module  208  may include code and routines configured to (1) adjust the barometric pressure data based on the acceleration of the vehicle  123  so that the barometric pressure data describes an acceleration-adjusted reading of the barometric pressure associated with the vehicle  123 , (2) adjust the location data  284  to include one or more bits of data describing the lane the vehicle  123  was located in while at the location, (3) determine an altitude for the lane based on the first barometric pressure data and (4) store altitude map data  282  describing the location data  284  and the altitude for the lane the vehicle  123  was located in while at the location. The altitude map data  282  may be stored by the analysis module  208  in a memory  227  of the barometric pressure system  200 . 
         [0210]    The analysis module  208  may also include code and routines configured to generate a geographic location vector for the vehicle  123  based on one or more of: (1) the location data  284 ; (2) a first speed of the vehicle  123 ; (3) the barometric pressure data describing the acceleration-adjusted reading of the barometric pressure associated with the vehicle  123 ; (4) the altitude map data  282 ; (5) a current time; (6) a direction of the vehicle  123  and (7) the an acceleration of the vehicle  123 . 
         [0211]    The barometric pressure system  123  may also include an onboard vehicle computer  182  communicatively coupled to memory  227 , the GPS system, the roadway imaging device, the set of first electronic sensor devices and the second electronic sensor device. The onboard vehicle computer  182  may be programmed by the analysis module  208  to (1) adjust the barometric pressure data based on the acceleration of the vehicle  123  so that the barometric pressure data describes an acceleration-adjusted reading of the barometric pressure associated with the vehicle  123 , (2) adjust the location data  284  to include one or more bits of data describing the lane the vehicle  123  was located in while at the location, (3) determine an altitude for the lane based on the first barometric pressure data and (4) store altitude map data  282  describing the location data  284  and the altitude for the lane the vehicle  123  was located in while at the location. 
         [0212]    In some implementations, the onboard vehicle computer  182  is further programmed by the analysis module  208  to generate a geographic location vector for the vehicle  123  based on one or more of: (1) the location data  284 ; (2) a first speed of the vehicle  123 ; (3) the barometric pressure data describing the acceleration-adjusted reading of the barometric pressure associated with the vehicle  123 ; (4) the altitude map data  282 ; (5) a current time; (6) a direction of the vehicle  123  and (7) the an acceleration of the vehicle  123 . 
         [0213]    In some implementations, the barometric pressure system  200  is an element a vehicle  123  that is autonomous or semi-autonomous. The barometric pressure system  200  may be configured to automatically steer the vehicle  123  based on an acceleration-adjusted barometric pressure determined by the analysis module  208 . 
         [0214]    The memory  227  of the barometric pressure system  208  may store altitude map data  282 . The altitude map data  282  may describe an altitude map for a geographic area and a plurality of altitudes associated with a plurality of lane locations included in the geographic area. 
         [0215]    The barometric pressure system  200  may also include a GPS system configured to determine location data  284  describing an estimate of a location of the vehicle  123 . The barometric pressure system  200  may also include a roadway imaging device configured to determine which lane the vehicle  123  is located in while at the location and detect an instance where a trajectory of the vehicle  123  will cause the vehicle  123  to leave the lane without authorization if not corrected. For example, the vehicle  123  may be on a path that will cause the vehicle to swerve into an adjacent lane, thereby endangering the safety of one or more drivers on the roadway. 
         [0216]    The barometric pressure system  200  may also include a set of first electronic sensor devices configured to record barometric pressure data describing a barometric pressure reading associated with the vehicle  123 . The barometric pressure system  200  may also include a second electronic sensor device configured to record acceleration data describing an acceleration of the vehicle  123 . 
         [0217]    The analysis module  208  of the barometric pressure system  200  may include code and routines configured to (1) adjust the barometric pressure data based on the acceleration of the vehicle  123  so that the barometric pressure data describes an acceleration-adjusted reading of the barometric pressure associated with the vehicle  123 , (2) determine an altitude-based geographic location of the vehicle  123  by analyzing the altitude map to identify a location having an altitude indicated by the barometric pressure data, (3) adjust the location data based on the altitude-based geographic location so that the location data  284  more accurately describes the location of the vehicle  123  and which lane the vehicle is located in while at the location, (4) determine a corrective action including which direction to steer the vehicle  123  so that the trajectory of the vehicle  123  will cause the vehicle  123  to remain in the lane and (5) cause the vehicle  123  to be steered based on the corrective action so that the trajectory of the vehicle  123  will cause the vehicle  123  to remain in the lane. 
         [0218]    The barometric pressure system  200  may also include an onboard vehicle computer  182  communicatively coupled to the GPS system, the roadway imaging device, the set of first electronic sensor devices and the second electronic sensor device. The onboard vehicle computer  182  may be programmed by the analysis module  208  to (1) adjust the barometric pressure data based on the acceleration of the vehicle  123  so that the barometric pressure data describes an acceleration-adjusted reading of the barometric pressure associated with the vehicle  123 , (2) determine an altitude-based geographic location of the vehicle  123  by analyzing the altitude map to identify a location having an altitude indicated by the barometric pressure data, (3) adjust the location data  284  based on the altitude-based geographic location so that the location data  284  more accurately describes the location of the vehicle  123  and which lane the vehicle  123  is located in while at the location, (4) determine a corrective action including which direction to steer the vehicle  123  so that the trajectory of the vehicle  123  will cause the vehicle  123  to remain in the lane and (5) cause the vehicle  123  to be steered based on the corrective action so that the trajectory of the vehicle  123  will cause the vehicle  123  to remain in the lane. 
         [0219]    In some implementations, the barometric pressure system  200  includes a network  105  communicatively coupled to a first mobile device  198  and a second mobile device  198  which is located at substantially the same altitude as the first mobile device  198 . The barometric pressure system  200  may also include a memory  227 . 
         [0220]    The first mobile device  198  may include a set of first electronic sensor devices, a second electronic sensor device and a first processor  225 . The set of first electronic sensor devices may be configured to record first barometric pressure data describing a first barometric pressure reading associated with the first mobile device  198 . The second electronic sensor device may be configured to record acceleration data describing an acceleration of the first mobile device  198 . 
         [0221]    The analysis module  208  of the barometric pressure system  200  may include code and routines configured to adjust the first barometric pressure data based on the acceleration of the first mobile device  198  so that the first barometric pressure data describes an acceleration-adjusted reading of the first barometric pressure associated with the first mobile device  198 . 
         [0222]    The first processor  225  may be communicatively coupled to the network  105 , the memory  227 , the set of first electronic sensor devices and the second electronic sensor device. The first processor  225  may be programmed by the analysis module  208  to adjust the first barometric pressure data based on the acceleration of the first mobile device  198  so that the first barometric pressure data describes an acceleration-adjusted reading of the first barometric pressure associated with the first mobile device  198 . 
         [0223]    The second mobile device  198  may be communicatively coupled to the network  105 . The second mobile device  198  may be configured to transmit second barometric pressure data describing a second barometric pressure associated with the second mobile device  198 . The second mobile device  198  may transmit the second barometric pressure data to the network  105 . 
         [0224]    The first processor  225 , which may also be communicatively coupled to the network  105 , may receive the second barometric pressure data from the network  105 . The analysis module  208  of the barometric pressure system  200  may include code and routines configured to determine a variance between the first barometric pressure and the second barometric pressure. For example, the smaller of the two barometric pressures may be subtracted from the larger of the two barometric pressures to determine the variance. The first processor  225  may be programmed by the analysis module  208  to determine the variance between the first barometric pressure and the second barometric pressure. 
         [0225]    The memory  227  may store a plurality of historical variances determined based on a plurality of second barometric pressure data received from a plurality of second mobile devices  198 . 
         [0226]    The analysis module  208  of the barometric pressure system  200  may include code and routines configured to analyze the variance and the historical variance to determine an adjustment for the acceleration-adjusted reading of the first barometric pressure so that the acceleration-adjusted reading of the first barometric pressure is more accurate. 
         [0227]    The first processor  225  of the first mobile device  198  may be programmed by the analysis module  208  to analyze the variance and the historical variance to determine an adjustment for the acceleration-adjusted reading of the first barometric pressure so that the acceleration-adjusted reading of the first barometric pressure is more accurate. 
         [0228]    In some implementations, the first mobile device  198  is a first vehicle  123 A and the second mobile device is a second vehicle  123 B. The second vehicle  123 B may be traveling in the same direction as the first vehicle  123  and passing the first vehicle  123 A. For example, the first mobile device  123 A is heading in a northbound direction in lane one of a freeway. The second mobile device  123 B is also heading in the northbound direction in lane two of the same freeway. The second mobile device  123 B is traveling at a faster speed than the first mobile device  123 A so that the second mobile device  123 B is passing the first mobile device  123 A. The barometric pressure system  200  may be an element of the first mobile device  123 A. 
         [0229]    The analysis module  208  may include code and routines configured to (1) determine vehicle motion and air flow noise associated with the second vehicle  123 B passing the first vehicle  123 A, (2) determine an effect of the vehicle motion and air flow noise on the acceleration-adjusted reading of the first barometric pressure associated with the first vehicle  123 A and (3) modify the acceleration-adjusted reading of the first barometric pressure so that the effect is filtered from the acceleration-adjusted reading of the first barometric pressure. 
         [0230]    In some implementations, the first processor  225  of the first vehicle  123 A is programmed by the analysis module  208  to (1) determine vehicle motion and air flow noise associated with the second vehicle  123 B passing the first vehicle  123 A, (2) determine an effect of the vehicle motion and air flow noise on the acceleration-adjusted reading of the first barometric pressure associated with the first vehicle  123 A and (3) modify the acceleration-adjusted reading of the first barometric pressure so that the effect is filtered from the acceleration-adjusted reading of the first barometric pressure. 
         [0231]    In some implementations, the first processor  225  of the first vehicle  123 A applies a signal processor to filter the effect from the acceleration-adjusted reading of the first barometric pressure. For example, the first processor  225  applies a Winsorising outlier filtering technique. 
         [0232]    In some implementations, the set of first electronic sensor devices and the second electronic sensor device are mounted in the first mobile device  123 A in a configuration designed to reduce the effect of the of the vehicle motion and air flow noise on the acceleration-adjusted reading of the first barometric pressure associated with the first mobile device  123 A. 
         [0233]    In some implementations, the barometric pressure system  200  includes a third mobile device  198 . The third mobile device  198  may be communicatively coupled to the network  105 . The third mobile device  198  may be configured to transmit third barometric pressure data describing a third barometric pressure associated with the third mobile device  198 . The third barometric pressure data may be transmitted to the network  105 . 
         [0234]    The third mobile device may include a stationary roadside device. For example, the third mobile device is an element of a traffic signal, a pedestrian crosswalk signal, a roadway camera system configured to monitor and determine traffic flow or detect traffic ordinance violations, a special-purpose device configured to provide the functionality of the third mobile device, or any other processor-based computing device mounted along a roadway. 
         [0235]    The analysis module  208  may include code and routines configured to determine a variance among two or more of the following: (1) the first barometric pressure associated with the first mobile device  198  or the first vehicle  123 A; the second barometric pressure associated with the second mobile device  198  or the second vehicle  123 B; and the third barometric pressure associated with the third mobile device  198 . 
         [0236]    The analysis module may also include code and routines configured to analyze (1) the variance associated with the first barometric pressure, the second barometric pressure and the third barometric pressure and (2) the historical variance to determine an adjustment for the acceleration-adjusted reading of the first barometric pressure so that the acceleration-adjusted reading of the first barometric pressure is more accurate. 
         [0237]    The first processor  225  may be programmed by the analysis module  208  to receive the third barometric pressure data from the wireless network and determine a variance among the first barometric pressure, the second barometric pressure and the third barometric pressure. The first processor may be further programmed by the analysis module  208  to analyze (1) the variance associated with the first barometric pressure, the second barometric pressure and the third barometric pressure and (2) the historical variance to determine an adjustment for the acceleration-adjusted reading of the first barometric pressure so that the acceleration-adjusted reading of the first barometric pressure is more accurate. 
         [0238]    In some implementations, the barometric pressure system  200  is an element of a vehicle  123  configured to determine three dimensional location data describing the three dimensional location of the vehicle  123 . The three dimensional location data may be stored on the memory  227 . The memory  227  may also store altitude map data  282 . The altitude map data  282  may describe an altitude map for a geographic area and a plurality of known barometric pressures associated with a plurality of locations included in the geographic area. The barometric pressure system  200  may include a GPS system configured to determine location data  284  describing an estimate of a location of the vehicle  123 . The barometric pressure system  200  may include a roadway imaging device configured to determine one or more items of interest surrounding the vehicle  123 . The barometric pressure system  200  may include a set of first electronic sensor devices configured to record barometric pressure data describing a barometric pressure reading associated with the vehicle  123 . The barometric pressure system  200  may include a second electronic sensor device configured to record acceleration data describing an acceleration of the vehicle  123 . 
         [0239]    The analysis module  208  of the barometric pressure system  200  may include code and routines configured to (1) adjust the barometric pressure data based on the acceleration of the vehicle  123  so that the barometric pressure data describes an acceleration-adjusted reading of the barometric pressure associated with the vehicle  123  and (2) determine the three dimensional location data describing the three dimensional location of a vehicle  123  based on the (a) one or more items of interest surrounding the vehicle  123  matching one or more known items of interest associated with the estimate of the location of the vehicle  123  and (b) the acceleration-adjusted reading of the barometric pressure associated with the vehicle  123  matching a known barometric pressure and a location associated with the matching known barometric pressure included in the altitude map. 
         [0240]    The barometric pressure system  200  may include an onboard vehicle computer  182  communicatively coupled to the GPS system, the roadway imaging device, the set of first electronic sensor devices and the second electronic sensor device. The onboard vehicle computer  182  may be programmed by the analysis module  208  to (1) adjust the barometric pressure data based on the acceleration of the vehicle  123  so that the barometric pressure data describes an acceleration-adjusted reading of the barometric pressure associated with the vehicle  123  and (2) determine the three dimensional location data describing the three dimensional location of a vehicle  123  based on the (a) one or more items of interest surrounding the vehicle  123  matching one or more known items of interest associated with the estimate of the location of the vehicle  123  and (b) the acceleration-adjusted reading of the barometric pressure associated with the vehicle  123  matching a known barometric pressure and a location associated with the matching known barometric pressure included in the altitude map. 
         [0241]    In some implementations, the barometric pressure system  200  is an element of a vehicle  123 . The barometric pressure system  200  may include a network  105  communicatively coupled to the vehicle  123  and a mobile device  198 . The vehicle  123  may include a first set of electronic sensor devices, a second electronic sensor device and an onboard vehicle computer  182 . The set of first electronic sensor devices may be configured to record first barometric pressure data describing a first barometric pressure reading associated with the vehicle  123 . The second electronic sensor device configured to record acceleration data describing an acceleration of the vehicle  123 . 
         [0242]    The vehicle  123  and the mobile device  198  may be communicatively coupled to the network  105 . The mobile device  198  may transmit second barometric pressure data describing a second barometric pressure reading associated with the mobile device  198 . The mobile device  198  may transmit second barometric pressure data to the network  105 . 
         [0243]    The analysis module  208  may determine an estimate of the altitude separation data based on the lateral differential data and data describe the known interval of increase or decrease in altitude for each unit of lateral distance. For example, the altitude may be known to increase or decrease at an estimated interval for each unit of lateral distance in a particular geographic area. Interval data describing the known interval of increase or decrease in altitude for each unit of lateral distance may be stored in the memory  227  or retrieved from the network. The interval data may be an element of the altitude map data  282 . 
         [0244]    The analysis module  208  may include code and routines configured to: (1) adjust the first barometric pressure data based on the acceleration of the vehicle  123  so that the first barometric pressure data describes an acceleration-adjusted reading of the first barometric pressure associated with the vehicle  123 , (2) determine a variance between the second barometric pressure reading and the acceleration-adjusted reading of the first barometric pressure associated with the vehicle  123 , (3) determine lateral differential data describing a lateral distance from the vehicle  123  and the mobile device  198  based on the variance and (4) determine an estimate of altitude separation between the vehicle  123  and the mobile device  198  based on the lateral differential data and interval data describing the known interval of increase or decrease in altitude for each unit of lateral distance. 
         [0245]    The onboard vehicle computer  182  of the vehicle  123  may be communicatively coupled to the network  105 , the set of first electronic sensor devices and the second electronic sensor device. The onboard vehicle computer  182  is programmed by the analysis module  208  to (1) adjust the first barometric pressure data based on the acceleration of the vehicle  123  so that the first barometric pressure data describes an acceleration-adjusted reading of the first barometric pressure associated with the vehicle  123 , (2) determine a variance between the second barometric pressure reading and the acceleration-adjusted reading of the first barometric pressure associated with the vehicle  123 , (3) determine lateral differential data describing a lateral distance from the vehicle  123  and the mobile device  198  based on the variance and (4) determine an estimate of altitude separation between the vehicle  123  and the mobile device  198  based on the lateral differential data and interval data describing the known interval of increase or decrease in altitude for each unit of lateral distance. 
         [0246]    In some implementations, the barometric pressure system  200  is an element of the vehicle  123 . The barometric pressure system  200  may include one or more third electronic sensor devices. The one or more third electronic devices may be configured to measure and record temperature and humidity associated with the vehicle  123 . For example, the one or more third electronic devices may measure and store environment data  280  describing the temperature and the humidity of the outside environment proximate to the vehicle  123 . In these implementations, the onboard vehicle computer  182  may be further programmed by the analysis module  208  to adjust the first barometric pressure data based on the acceleration, the temperature and the humidity associated with the vehicle  123 . 
         [0247]    In some implementations, the analysis module  208  includes codes and routines configured to determine whether the alarm system  250  will trigger a collision threat alarm based at least in part on the lateral differential data and the estimate of altitude separation between the vehicle  123  and the mobile device  198 . 
         [0248]    In some implementations, the sensor set  252  may include one or more MEMS sensors configured to measure barometric pressure. The barometric pressure data may be determined based on MEMS sensor deflection and the temperature of the MEMS sensor. Deflection nonlinearity may indicate inaccuracy in the readings of the MEMS sensor. The nonlinearity may be corrected by the calibration module  210  using calibration data determined by the analysis module  208  based on a calibrated pressure source (e.g., a barometric pressure reading received from another object) and a temperature reading taken from the onboard temperature sensor of the vehicle  123  or mobile device  198 . The MEMS sensor may include a non-transitory, non-volatile memory such as memory  227 . The calibration data may be stored in the memory of the MEMS sensor and used to calibration the barometric pressure data recorded by the MEMS sensor. 
         [0249]    In some implementations, the analysis module  208  may determine the differential barometric pressure for two objects based at least in part on a temperature of a column of air between the objects and in part by the temperature of the MEMS sensor. For example, temperature of the MEMS sensor may affect the barometric pressure measurement provided by the MEMS sensor. The value of the barometric pressure measurement provided by the MEMS sensor may vary based on temperature measured on the MEMS sensor. Similarly, the estimated separation distance between the objects based on the column of air may also vary based on the measured temperature of the column of air. 
         [0250]    In some implementations, the barometric pressure system  200  is configured to provide data describing an estimate of the elevation of the object which includes the barometric pressure system  200  to within plus or minus 3 meters of the actual elevation of the object. 
         [0251]    In some implementations, the barometric pressure system  200  may be implemented using hardware including a field-programmable gate array (“FPGA”) or an application-specific integrated circuit (“ASIC”). In some other implementations, the barometric pressure system  200  may be implemented using a combination of hardware and software. The barometric pressure system  200  may be stored in a combination of the devices and servers, or in one of the devices or servers. 
       Example Environment Data  280  and Motion Data  290   
       [0252]      FIG. 2B  is a block diagram illustrating an example of the environment data  280 . The environment data  280  may include one or more of the following: barometric pressure data  291 ; temperature data  292 ; altitude data  293 ; humidity data  203 ; and roadway imaging data  205 . 
         [0253]    The barometric pressure data  291  may describe one or more measurements of the barometric pressure proximate to the device which includes the barometric pressure system  200 . “Proximate to the device” may include the column of air above the device. The barometric pressure reading described by the barometric pressure data  291  may be measured and recorded, for example, by one or more barometric pressure sensors included in the sensor set  252 . The barometric pressure data  291  may be adjusted based on the forces affecting the device which includes the barometric pressure system  200 . For example, the barometric pressure data  291  may be adjusted based on one or more of the following: acceleration; temperature; humidity; roadway noise; or the forces described by the motion data  290 . In some implementations, the barometric pressure data  291  may describe the differential barometric pressure determined by the analysis module  208  and used to determine the estimate of altitude separation. 
         [0254]    The temperature data  292  may describe one or more measurements of the temperature proximate to the device which includes the barometric pressure system  200 . The temperature reading described by the temperature data  292  may be measured and recorded, for example, by one or more temperature sensors included in the sensor set  252 . The temperature sensor may include an onboard temperature sensor of a vehicle  123 . 
         [0255]    The altitude data  293  may describe one or more altitudes received in a DSRC communication or included in data from a GPS signal. The altitude data  293  is described in more detail below with reference to  FIG. 11 . For example, a DSRC full position vector may include data describing the elevation or the altitude of an object which transmits the DSRC full position vector. 
         [0256]    The humidity data  203  may describe one or more measurements of the humidity proximate to the device which includes the barometric pressure system  200 . The humidity reading described by the humidity data  203  may be measured and recorded, for example, by one or more humidistats, humidity sensors or moisture sensors included in the sensor set  252 . 
         [0257]    The roadway imaging data  205  may describe one or more images of the roadway proximate to the device which includes the barometric pressure system  200 . The roadway images described by the roadway imaging data  205  may be captured, for example, by one or more cameras or range imaging systems included in the sensor set  252 . 
         [0258]    The environment data  280  may include other data. For example, the environment data  280  may include data describing any physical attribute of the environment proximate to the device which includes the barometric pressure system  200 . 
         [0259]      FIG. 2C  is a block diagram illustrating an example of the motion data  290 . The motion data  290  may include one or more of the following: gyrometer data  294 ; accelerometer data  295 ; and wheel motion data  296 . 
         [0260]    The gyrometer data  294  may describe one or more measurements of the orientation of the device which includes the barometric pressure system  200 . The gyrometer data  294  may describe any measurements of the one or more gyrometers. The orientation reading described by the gyrometer data  294  may be measured and recorded, for example, by one or more gyrometers included in the sensor set  252 . The gyrometer data  294  may describe any measurements of the one or more gyrometers. 
         [0261]    The accelerometer data  295  may describe one or more recordings of the acceleration of the device which includes the barometric pressure system  200 . The acceleration reading described by the accelerometer data  295  may be measured and recorded, for example, by one or more accelerometers included in the sensor set  252 . 
         [0262]    In some implementations, the barometric pressure system  200  is an element of a mobile device  198 . For example, the barometric pressure system  200  is an element of a smartphone. A driver of a vehicle  123  may be traveling with the smartphone. The accelerometer data  295  may describe the acceleration of the vehicle  123 . 
         [0263]    The wheel motion data  296  may describe the motion of a steering wheel of a vehicle  123  which includes the barometric pressure system  200 . 
         [0264]    The motion data  290  may include other data. For example, the motion data  290  may include data describing any dynamic motion of a device which includes the barometric pressure system  200  or a device which is proximate to the device which includes the barometric pressure system  200 . 
       Altitude Separation 
       [0265]      FIG. 3  is a block diagram illustrating an operating environment  300  including an example altitude separation between a first vehicle  123 A and a second vehicle  123 B according to some implementations. The top of the Earth&#39;s atmosphere may be indicated by element  305 . For the purposes of explanation, assume that the top of the Earth&#39;s atmosphere is 230,000 feet above sea level. Lines “A” and “B” may indicate boundaries forming a column of air starting at the surface of the Earth and extending to the top of the Earth&#39;s atmosphere. The column of air formed by lines “A” and “B” will be referred to herein as “the column of air.” 
         [0266]    A first roadway may be indicated by element  335 . The first roadway  335  may be located on the surface of the Earth. A first vehicle  123 A may be traveling on the first roadway. A second roadway may be indicated by element  330 . The second roadway is located at an altitude that is higher than the first roadway. A second vehicle  123 B is traveling on the second roadway. The estimate of altitude separation between the first vehicle  123 A and the second vehicle  123 B is indicated by element  325 . 
         [0267]    Element  310  may indicate an altitude of approximately 27,900 feet above the surface of the Earth. 
         [0268]    Element  320  may indicate a portion of the column of air that corresponds to air parameters associated with the first vehicle  123 A. The air parameters for the first vehicle  123 A and element  320  may include the pressure (i.e., barometric pressure), humidity and temperature associated with the column of air which corresponds to the first vehicle  123 A. 
         [0269]    Element  315  may indicate a portion of the column of air that corresponds to air parameters associated with the second vehicle  123 B. The air parameters for the second vehicle  123 B and element  315  may include the pressure (i.e., barometric pressure), humidity and temperature associated with the column of air which corresponds to the second vehicle  123 B. 
         [0270]    Element  340  is a signal line indicating that the first vehicle  123 A and the second vehicle  123 A each include wireless antenna hardware (e.g., communication unit  245 ) configured to enable wireless object-to-object communication with one another. For example, the element  340  may indicate that the first vehicle  123 A and the second vehicle  123 B may communicate with one another via one or more of the following: DSRC; Wi-Fi; Bluetooth™; etc. 
         [0271]    The first vehicle  123 A may include a first barometric pressure system  200  and the second vehicle  123 B may include a second barometric pressure system  200 . The first barometric system  200  of the first vehicle  123 A may measure and record the air parameters associated with the first vehicle  123 A and element  320 . The second barometric system  200  of the second vehicle  123 B may measure and record the air parameters associated with the second vehicle  123 B and element  315 . The vehicles  123 A,  123 B may wirelessly communicate their air parameters to one another via the signal line  340 . 
         [0272]    Example deficiencies of the prior art barometric pressure systems will now be described. Element  335  indicates a first roadway. Assume that the first roadway  335  is located at zero feet above sea level and that the column of air is located above a point on the first roadway  335  that is in the proximity of the first vehicle  123 A. 
         [0273]    Prior art barometric pressure systems always rely on absolute barometric pressure that is adjusted for humidity and temperature. Any measurement of absolute barometric pressure that is adjusted for humidity is a humidity-adjusted absolute barometric pressure measurement. Any measurement of absolute barometric pressure that is adjusted for temperature is a temperature-adjusted absolute barometric pressure measurement. Any measurement that is adjusted for humidity and temperature is a humidity and temperature-adjusted absolute barometric pressure measurement. By contrast, in some implementations the barometric pressure system  199 ,  200  may include a standard air column temperature and humidity for generating the transmitted barometric pressure. In some implementations, the barometric pressure system  199 ,  200  further contrasts with prior art barometric pressure systems by using a MEMs sensor temperature measurement for adjusting a calibration of a MEMs barometric pressure measurement. 
         [0274]    Prior art barometric pressure systems generally provide a humidity and temperature-adjusted absolute barometric pressure measurement. For example, the absolute barometric pressure above the point in the first roadway  335  is a function of the weight of the column of air from zero feet above sea level (as indicated by element  335 ) to 230,000 feet above sea level (e.g., as indicated by element  305 ). Prior art barometric pressure systems work in the following way: (1) a barometric pressure sensor may measure absolute barometric pressure at the point on the first roadway  335 ; (2) a temperature sensor measures the temperature of the column of air; (3) a humidity sensor measures the humidity of the column of air; (4) the prior art barometric pressure system then adjust the reading of absolute barometric pressure based on (a) the temperature of the column of air and (b) the humidity of the column of air; and (5) the prior art barometric pressure system outputs a humidity and temperature-adjusted absolute barometric pressure measurement. Prior art barometric pressure systems never rely on the relative barometric pressure measurements between two objects or two points. 
         [0275]    A typical humidity and temperature-adjusted absolute barometric pressure measurement at sea level (as indicated by element  335 ) is about 1 bar or 1,000 millibar. Absolute barometric pressure is generally inversely proportional to altitude. In other words, absolute barometric pressure generally decreases with an increase in altitude. Assuming a temperature of 60 degrees Fahrenheit, an increase in altitude of 27.4 feet generally corresponds to a decrease in absolute barometric pressure by 1 millibar. For example, assuming a temperature of 60 degrees Fahrenheit, absolute barometric pressure may be 1,000 millibars at sea level (as indicated by element  335 ) and then decrease to 999 millibars as the altitude increases to 27.4 feet above sea level and the temperature remains substantially constant. 
         [0276]    Absolute and relative measurements of barometric pressure may be used to estimate the altitude of objects. For example, if a barometric pressure sensor indicates an absolute barometric pressure measurement of 999 millibars and the temperature is 60 degrees Fahrenheit, then the estimated altitude of the sensor is substantially 27.4 feet above sea level. An absolute barometric pressure measurement of 998 millibars at a temperature of 60 degrees Fahrenheit corresponds to an estimated altitude of 54.8 feet above sea level. Accordingly, a change in the reading of absolute barometric pressure indicates a significant change in altitude when applied to a paradigm where the barometric pressure measurements are used for determining the altitude of objects located on the ground such as vehicles and mobile devices. 
         [0277]    For example, referring to  FIG. 3 , element  335  is a first roadway and element  330  is a second roadway. The second roadway  330  is an overpass which is above the first roadway  335 . A typical overpass is elevated about 35 feet above other roadways. For example, the second roadway  330  is 35 feet above the first roadway  335 . A consequence of this is that prior art barometric pressure measurements may not be used to determine whether a first vehicle  123 A traveling on the first roadway  335  is at the same altitude as a second vehicle  123 B traveling on the second roadway  330 . 
         [0278]    For example, assume that the operating environment  300  is located in Denver, Colo. The highest point in Denver is 5,690 feet above sea level. In this example, the first roadway  335  is 5,690 feet above sea level. Humidity and temperature sensors are inaccurate, particularly so when measuring humidity across a column of air as in  FIG. 3 . The accuracy of a humidity sensor measuring humidity across a column of air as in  FIG. 3  is generally plus or minus 10% and the accuracy of a temperature sensor measuring temperature across a column of air is generally plus or minus 1%. Experimentation has shown that determining altitude using absolute barometric pressure measurements that are adjusted for humidity results in a plus or minus 1% miscalculation of altitude. In other words, using a prior art barometric pressure system, the altitude of the first roadway  335  may be determined to be anywhere from 5,746.9 feet (1% greater than 5,690 feet) to 5,633.1 feet (1% less than 5,690 feet). 
         [0279]    Assume that the first vehicle  123 A and the second vehicle  123 B are both traveling on the first roadway  330 . Using prior art barometric pressure systems, the first vehicle  123 A may be determined to be traveling at an altitude of 5,633.1 feet and the second vehicle  123 B may be determined to be traveling at an altitude of 5,746.9 feet. If the first vehicle  123 A includes an alarm system  250  and a prior art barometric pressure system, then the onboard vehicle computer  182  of the first vehicle  123 A may erroneously determine that the first vehicle  123 A and the second vehicle  123 B are located at different altitudes, and so, it is safe to suppress a collision threat alarm incident. The consequence of this error may be that the first vehicle  123 A and the second vehicle  123 B collide and humans are killed. Because of this, prior art barometric pressure systems are not compatible with safety systems that determine the altitude of objects such as vehicles and mobile devices. 
         [0280]    By contrast, the barometric pressure system  199 ,  200  of  FIGS. 1 and 2A  always rely on relative barometric pressure measurements, which has been proven by experimentation to be sufficiently accurate for safety systems that determine the altitude of objects such as vehicles and mobile devices. For example, the barometric pressure system  199 ,  200  always determines a differential barometric pressure for two objects. The barometric pressure system  199 ,  200  may then determine an altitude separation for the two objects based at least in part on the differential barometric pressure value. 
         [0281]      FIG. 4  is a chart  400  depicting barometric pressure variation during an example first journey according to some implementations. In this example, “work” is a location in Mountain View, Calif. and that home is a location in Los Altos Hills, Calif. 
         [0282]      FIG. 5  is a chart  500  depicting barometric pressure variation during an example second journey according to some implementations. In this example, “work” is a location in Mountain View, Calif. that is 86 feet above sea level and the Shoreline Kayak Ramp is a location in Mountain View, Calif. that is 0 feet above sea level. The second journey goes from work to the Shoreline Kayak Ramp and then back to work. The portion of the journey located at the Shoreline Kayak Ramp corresponds to the pressure data of the X and Y axis converging on zero. 
         [0283]      FIG. 6  is a block diagram illustrating an example process flow  600  for determining a sensor signal output according to some implementations. A plurality of sensors provides an input to a manufacturing and material technology parameter derived outlier filter. The signal may include sensor data. The manufacturing and material technology parameter derived outlier filter processes the signal and outputs a signal to a Winsorising outlier filter. The Winsorising outlier filter processes the signal and outputs a signal to a linear signal filter. The linear signal filter processes the signal and outputs a sensor signal output. The processor flow  600  may be an example of signal processing implemented by the processor  225 . The processor  225  may be programmed to implement the process flow  600  by the analysis module  208 . 
         [0284]      FIG. 7  is a block diagram of a system  700  for generating altitude map data  282  describing an altitude map for a geographic area. The first vehicle  123 A may include a barometric pressure system  200 . The first vehicle  123 A may be traveling in a geographic area. As the first vehicle  123 A travels, it may record data describing one or more of the following: its present location; the present time; and the barometric pressure recorded at the location and time. This data may be stored in a memory  710  as altitude map data  282 . The memory  710  may include a non-transitory storage medium such as memory  227  described above with reference to  FIG. 2A . The altitude map data  282  may be transmitted to the network  105 . As the first vehicle  123 A is on a journey, a cell tower  705  may receive the altitude map data  282  and transmit it to a server such as server  155 . If the first vehicle parks at a trusted location  715  such as a home or work place, then the altitude map data  282  may be wirelessly transmitted to a memory  720  of the trusted location  715 . The memory may be a non-transitory memory of a wireless router  717 . The wireless router  717  may then transmit the altitude map data  282  to a server such as server  155  via the network  105 . 
         [0285]      FIG. 8  is a block diagram of an example barometric pressure system  800  according to some implementations. 
         [0286]      FIG. 9  is a chart  900  depicting a specification of an example barometric pressure sensor included in the sensor set  252  of the barometric pressure system  200  according to some implementations. 
         [0287]      FIGS. 10A and 10B  are charts depicting example data that may be stored in a memory. 
         [0288]      FIG. 11  is a block diagram illustrating an example DSRC full position vector  1100  according to some implementations. The DSRC full position vector  1100  includes data describing, among other things, time, latitude and longitude (e.g., location data  284 ), altitude (e.g., barometric pressure data  291  or altitude data  293 ), speed and confidence factors (e.g., quality data  297  related to sensors that measured the time, latitude and longitude, altitude (or elevation) and speed). 
         [0289]    In some implementations, the DSRC full position vector  1100  may be an example of object data  286  transmitted from one object to another object. An example of this is described in more detail below with reference to  FIGS. 14 and 15 . 
         [0290]      FIG. 12  is a chart  1200  depicting a specification of an example capacitive humidity sensor included in the sensor set  252  of the barometric pressure system  200 . 
         [0291]      FIG. 13  is a chart  1300  depicting a specification of an example thermistor temperature sensor included in the sensor set  252  of the barometric pressure system  200 . 
         [0292]      FIG. 14  is a block diagram of an operating environment  1400  including a first vehicle  123 A and a second vehicle  123 B wirelessly communicating with one another via DSRC. The second vehicle  286  includes object data  286 . The object data  286  may describe a barometric pressure measurement recorded by a second barometric pressure system  200  (not pictured) that is an element of the second vehicle  123 B. 
         [0293]    The second vehicle  123 B is communicatively coupled to the first vehicle  123 A. A signal line  1405  indicates a wireless communicative coupling between the second vehicle  123 B and the first vehicle  123 A. The signal line  1405  may indicate a DSRC communication among the second vehicle  123 B and the first vehicle  123 A. 
         [0294]    The second vehicle  123 B may provide the object data  286  to the first vehicle  123 A via the wireless communication indicated by the signal line  1405 . The object data  286  depicted with a dashed line and located above element  1405  indicates the object data  286  is being provided to the first vehicle  123 A. 
         [0295]    The first vehicle  123 A may include a first barometric pressure system  200  (not pictured). The first barometric pressure system  200  may include a calibration module  210 . The first vehicle  123 A and the second vehicle  123 B may be located at substantially the same altitude. 
         [0296]    The first vehicle  123 A may use the object data  286  to determine if the sensor set  252  (not pictured) of the first vehicle  123 A is to be calibrated. For example, the object data  286  may include the barometric pressure data  291  of the second vehicle  123 B. The object data  286  may include quality data  297  indicating the quality of the barometric pressure data  291  of the second vehicle  123 B. The analysis module  208  (not pictured) of the first vehicle  123 A may compare the barometric pressure data  291  of the second vehicle  123 B to barometric pressure data of the first vehicle  123 A. The analysis module  208  of the first vehicle  123 A may determine, based at least in part on the object data  286 , that one or more electronic sensors of the sensor set  252  (not pictured) included in the first vehicle  123 A is to be calibrated. 
         [0297]    Optionally, one or more of the first vehicle  123 A and the second vehicle  123 B may be a mobile device  198 . 
         [0298]      FIG. 15  is a block diagram of an operating environment  1500  including a vehicle  123  and a stationary roadside device  1510  wirelessly communicating with one another via DSRC. 
         [0299]    The stationary roadside device  1510  includes object data  286 . The object data  286  may describe a barometric pressure measurement recorded by a second barometric pressure system  200  (not pictured) that is an element of the stationary roadside device  1510 . 
         [0300]    The stationary roadside device  1510  is communicatively coupled to the vehicle  123 . A signal line  1505  indicates a wireless communicative coupling between the stationary roadside device  1510  and the vehicle  123 . The signal line  1505  may indicate a DSRC communication among the stationary roadside device  1510  and the vehicle  123 . 
         [0301]    The stationary roadside device  1510  may provide the object data  286  to the vehicle  123  via the wireless communication indicated by the signal line  1505 . The object data  286  depicted with a dashed line and located above element  1505  indicates the object data  286  is being provided to the vehicle  123 . 
         [0302]    The vehicle  123  may include a first barometric pressure system  200  (not pictured). The first barometric pressure system  200  may include a calibration module  210 . The vehicle  123  and the stationary roadside device  1510  may be located at substantially the same altitude. 
         [0303]    The vehicle  123  may use the object data  286  to determine if the sensor set  252  (not pictured) of the vehicle  123  is to be calibrated. For example, the object data  286  may include the barometric pressure data  291  of the stationary roadside device  1510 . The object data  286  may include quality data  297  indicating the quality of the barometric pressure data  291  of the stationary roadside device  1510 . The analysis module  208  (not pictured) of the vehicle  123 A may compare the barometric pressure data  291  of the stationary roadside device  1510  to barometric pressure data of the vehicle  123 A. The analysis module  208  of the vehicle  123  may determine, based at least in part on the object data  286 , that one or more electronic sensors of the sensor set  252  (not pictured) included in the vehicle  123  is to be calibrated. 
         [0304]      FIG. 16  is a block diagram of a system  1600  including a vehicle  123 . The vehicle  123  includes a first set of electronic sensor devices  1605 A,  1605 B,  1605 C and a second electronic sensor device  1610 . The first set of electronic sensor devices  1605 A,  1605 B,  1605 C may include a plurality of barometric pressure sensors. The second electronic sensor device  1610  may include an accelerometer. Element  1615  indicates a vehicle acceleration force and a gravitational acceleration force applied to the vehicle  123 . The second electronic sensor device  1610  may measure the vehicle acceleration force and the gravitational acceleration force of element  1615 . The first set of electronic sensor devices  1605 A,  1605 B,  1605 C may be distributed in the vehicle  123  to account for forces applied to the vehicle  123  and to minimize the effect of these forces based on the acceleration measured by the second electronic sensor device  1610 . 
         [0305]    For example, the first set of electronic sensor devices  1605 A,  1605 B,  1605 C may be distributed in the vehicle  123  so that the barometric pressure system  200  of the vehicle  123  may: (1) measure and record the acceleration of the vehicle  123 ; (2) detect the impact of acceleration on the measurement of barometric pressure by one or more of the electronic sensor devices  1605 A,  1605 B,  1605 C; (3) quantify the effect of the acceleration on the barometric pressure measurement recorded by one or more of the electronic sensor devices  1605 A,  1605 B,  1605 C; and (4) adjust the barometric pressure data  291  recorded by the electronic sensor devices  1605 A,  1605 B,  1605 C affected by the acceleration of the vehicle  123  so that the barometric pressure data  291  describes an acceleration-adjusted reading of the barometric pressure associated with the vehicle  123 . For example, some of the electronic sensor devices  1605 A,  1605 B,  1605 C may not be affected by the acceleration of the vehicle  123  based on their placement within the vehicle  123  while other electronic sensor devices  1605 A,  1605 B,  1605 C may be affected. The barometric pressure system  200  may determine which electronic sensor devices  1605 A,  1605 B,  1605 C were affected and adjust the barometric pressure data  291  associated with the affected electronic sensor devices  1605 A,  1605 B,  1605 C so that the barometric pressure data  291  is more accurate because it is not affected by the acceleration of the vehicle  123 . The barometric pressure data  291  may also be adjusted based on noise caused by open windows of the vehicle or a vehicle ventilation system. 
         [0306]    The implementations of the specification can also relate to an apparatus for performing the operations described herein. This apparatus may be specially constructed for the required purposes, or it may include a special-purpose computer selectively activated or reconfigured by a computer program stored in the computer. Such a computer program may be stored in a non-transitory computer-readable storage medium, including, but is not limited to, any type of disk including floppy disks, optical disks, CD-ROMs, and magnetic disks, read-only memories (ROMs), random access memories (RAMs), EPROMs, EEPROMs, magnetic or optical cards, flash memories including USB keys with non-volatile memory, or any type of media suitable for storing electronic instructions, each coupled to a computer system bus. 
         [0307]    The specification can take the form of some entirely hardware implementations, some entirely software implementations, or some implementations containing both hardware and software elements. In some implementations, the specification is implemented in software, which includes, but is not limited to, firmware, resident software, microcode, etc. 
         [0308]    Furthermore, the description can take the form of a computer program product accessible from a computer-usable or computer-readable medium providing program code for use by or in connection with a computer or any instruction execution system. For the purposes of this description, a computer-usable or computer-readable medium can be any apparatus that can contain, store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device. 
         [0309]    A data processing system suitable for storing or executing program code will include at least one processor coupled directly or indirectly to memory elements through a system bus. The memory elements can include local memory employed during actual execution of the program code, bulk storage, and cache memories which provide temporary storage of at least some program code in order to reduce the number of times code must be retrieved from bulk storage during execution. 
         [0310]    Input/output or I/O devices (including, but not limited to, keyboards, displays, pointing devices, etc.) can be coupled to the system either directly or through intervening I/O controllers. 
         [0311]    Network adapters may also be coupled to the system to enable the data processing system to become coupled to other data processing systems or remote printers or storage devices through intervening private or public networks. Modems, cable modem, and Ethernet cards are just a few of the currently available types of network adapters. 
         [0312]    Finally, the algorithms and displays presented herein are not inherently related to any particular computer or other apparatus. Various general-purpose systems may be used with programs in accordance with the teachings herein, or it may prove convenient to construct more specialized apparatus to perform the required method steps. The required structure for a variety of these systems will appear from the description below. In addition, the specification is not described with reference to any particular programming language. It will be appreciated that a variety of programming languages may be used to implement the teachings of the specification as described herein. 
         [0313]    The foregoing description of the implementations of the specification has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the specification to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. It is intended that the scope of the disclosure be limited not by this detailed description, but rather by the claims of this application. As will be understood by those familiar with the art, the specification may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. Likewise, the particular naming and division of the modules, routines, features, attributes, methodologies, and other aspects are not mandatory or significant, and the mechanisms that implement the specification or its features may have different names, divisions, or formats. Furthermore, the modules, routines, features, attributes, methodologies, and other aspects of the disclosure can be implemented as software, hardware, firmware, or any combination of the three. Also, wherever a component, an example of which is a module, of the specification is implemented as software, the component can be implemented as a standalone program, as part of a larger program, as a plurality of separate programs, as a statically or dynamically linked library, as a kernel-loadable module, as a device driver, or in every and any other way known now or in the future to those that practice the art of computer programming. Additionally, the disclosure is in no way limited to implementations in any specific programming language, or for any specific operating system or environment. Accordingly, the disclosure is intended to be illustrative, but not limiting, of the scope of the specification, which is set forth in the following claims.