[ale] WAY [OT] but geeky - how do I calibrate GPS barometric altimeter

[Mike Harrison]

Ya'll do realize that the pressure changes constantly, right?

http://en.wikipedia.org/wiki/Atmospheric_pressure

Measure the same spot for a few days...


btw:

Androsensor on an Android phone with a barometer is pretty kewl..

And it shows me at 983.29 millibars or approx 252.3 meters / 827.9 feet
at my desk at work. And now that I have a record, I wonder what tomorrows 
will be.






On Mon, 25 Feb 2013, Pete Hardie wrote:

> Go down to the airport - it's a well-specified lat/lon and alt, and a weather station.
> 
> Pete Hardie
> --------
> Better Living Through Bitmaps
> 
> 
> On Mon, Feb 25, 2013 at 5:53 PM, Ron Frazier (ALE) <atllinuxenthinfo at techstarship.com> wrote:
>       Hi all,
>
>       I just got my hands on a neat Garmin Etrex Vista H handheld GPS on clearance for hiking trails and such.  It has a barometric
>       altimeter that I wish to calibrate.  I have to either enter an accurate known  barometric pressure; or I have to enter an
>       accurate known elevation.
>
>       I've checked Weatherbug (for Cumming, GA), The Weather Channel, and the Firefox ForecastFox plugin.
>
>       The barometric pressure readings are: 29.85, 29.92, and 29.90.  As I understand it, these variations would be enough to create
>       altimeter reading differences of around 70 feet.
>
>       I can't necessarily use my weather station as a good barometric pressure gauge, since it depends on elevation.  (I usually
>       calibrate that instrument by putting in the barometric pressure from The Weather Channel.)
>
>       I don't know the exact elevation of my house, nor the exact elevation at the trail at the park.
>
>       I can calibrate to GPS elevation, but that's not very accurate.
>
>       Garmin says the altimeter is accurate to 10 feet if properly calibrated.  Of course, it will change with the weather.
>
>       So, how can I determine accurate barometric pressure for a location, or accurate elevation, so I can calibrate this thing?  Is
>       there a way to get elevation from google maps, or something?
>
>       Note, this is not critical, not life threatening if I don't find the answer, not even exceedingly important.  But, I just want
>       to get the most usage out of the device that I can.  And, you guys are a great source of geeky information of all sorts.
>
>       Any help, as always, is appreciated.
>
>       Sincerely,
>
>       Ron
> 
>
>       --
>
>       (PS - If you email me and don't get a quick response, you might want to
>       call on the phone.  I get about 300 emails per day from alternate energy
>       mailing lists and such.  I don't always see new email messages very quickly.)
>
>       Ron Frazier
>       770-205-9422 (O)   Leave a message.
>       linuxdude AT techstarship.com
>
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