Support the barometer on the Galaxy Nexus

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The barometer on the Galaxy Nexus should give a more accurate altitude than 
doea GPS.

Original issue reported on code.google.com by dgehlhaa...@gmail.com on 28 Dec 2011 at 3:51

• Merged into: #553

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Please notice a barometer doesn't give an altitude reading - it just gives a 
barometric pressure. Getting an altitude from that involves other variables 
that have to be measured (e.g. QNH) and which the device has no good way to 
determine (or at least not with enough precision to be of use for determining a 
precise altitude. The closest we could get would be reading QNH from METAR, but 
the potential distance from the current position to the closest METAR station 
can be up to hundreds of miles (afaik only Europe has a dense METAR network), 
so the reading would still be imprecise.

What the barometer can measure correctly, though, is altitude variation - 
knowing that you climbed or descended X feet along your ride - the pressure 
variation is pretty much linear in low altitudes (low as in, anywhere on the 
surface of the planet).

Original comment by rdama...@google.com on 28 Dec 2011 at 4:52

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Two notes.

1) The way that this is usually handled on GPS devices is that they let you 
calibrate the altimeter by entering a known altitude for your current location. 
 This is how, e.g. GARMIN devices do this.

2) Reasonable defaults are likely to give very usable results, e.g. 30.00 
inches / 1000 mB = zero elevation.  This will hold quite well -- and provide 
more accurate data than does GPS -- unless you are living in an extreme weather 
area.

Original comment by dgehlhaa...@gmail.com on 28 Dec 2011 at 7:39

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For sport tracking change in height is more important than absolute height. 
Using a GPS height as the initial value would do. Even better would be an 
average of GPS heights over a reasonable period compared to an average from the 
barometer over the same period. Then height = (barometer - average barometer) x 
scaling value + average GPS height.

Original comment by kenep...@gmail.com on 29 Dec 2011 at 9:29

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Original comment by sandordo...@google.com on 20 Jan 2012 at 5:11

• Changed state: Duplicate