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Topic # 113319 13-Jan-2013 20:02
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A few newer phones like my Nexus 4 have a barometer to measure air pressure. Apparently this is used by the phone’s GPS system to determine your altitude to get a faster GPS lock.

I have seen a few apps that do something interesting with this data, one of these is pressureNET which crowd sources the data and displays it on a map (screenshot below). You can also get your own devices trend over time.


Anyone else find an interesting use for the barometer?

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BDFL - Memuneh
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  Reply # 744197 13-Jan-2013 20:25
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Interesting... Using a barometer to represent altitude? These measure atmospheric pressure, and this varies depending on conditions, even on same altitude. Not sure this can help GPS that much. AGPS helps with a coarse location and from there it is easier for the GPS to know where to "look for" signals in the sky. Once there are enough signals then the GPS can have a fine location and altitude.

From the link: "The primary purpose of the barometer is (at least, I've been told)..." sounds more like "a friend of a friend told me" than first hand technical knowledge.







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  Reply # 744211 13-Jan-2013 20:39
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Well Dan Morrill (the author of the post) is an android engineer working Google so I assume that he got good advice!

But yes my thoughts were the same as yours regarding weather conditions affecting the barometer, perhaps it is just "good enough" for the job, if a bit inaccurate.

 
 
 
 


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  Reply # 744214 13-Jan-2013 20:43
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freitasm: Interesting... Using a barometer to represent altitude? These measure atmospheric pressure, and this varies depending on conditions, even on same altitude. Not sure this can help GPS that much. AGPS helps with a coarse location and from there it is easier for the GPS to know where to "look for" signals in the sky. Once there are enough signals then the GPS can have a fine location and altitude.

From the link: "The primary purpose of the barometer is (at least, I've been told)..." sounds more like "a friend of a friend told me" than first hand technical knowledge.



The Barometer provides course altitude information to the GPS, a little like the a-GPS gives course 2D data.

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  Reply # 744220 13-Jan-2013 20:50
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freitasm: Interesting... Using a barometer to represent altitude? These measure atmospheric pressure, and this varies depending on conditions, even on same altitude. Not sure this can help GPS that much.


Barometers are the primary method of determining altitude in a lot of electronic devices.. including dedicated GPS receivers. Also prominent here are altimeters for hobby rocketry.




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  Reply # 744294 13-Jan-2013 22:15
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They can be used for altitude sure, but they aren't absolute as the pressure varies with weather conditions. That's all.





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  Reply # 744301 13-Jan-2013 22:42
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Altitude (or the 'Z' vector ) is the least accurate component of a GPS fix.
But I can see how Google would use it to assist to a fix. It's likely they use reference information from local sources, which would be used to get a local offset over a larger area, that way the device barometer would provide users with a faster first fix and Google would/could improve their maps for 3D and collect a more accurate reference geoid....

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  Reply # 744558 14-Jan-2013 14:31
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freitasm: They can be used for altitude sure, but they aren't absolute as the pressure varies with weather conditions. That's all.



Remember that Google will know the mean sea level pressure for anywhere in the world so would be able to use that as a reference for altitude...

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