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Phone Barometer/Altimeter

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Phone Barometer/Altimeter

Postby jdorje » Thu Apr 25, 2013 5:55 pm

Got a new Android (note), and this one has a barometer. Seems like there's no respectable software to use the barometer, so I made a quick test app for measuring pressure and calculating altitude from it.

Accuracy is hard to tell, since calibration is not easy. Ambient sea level pressure can be downloaded from the internet, but doesn't seem very consistent at all for an out-of-the-way location.

But the first thing I noticed was the incredible precision: I'd say there is about +-1 foot of error to it (individual measurements have a higher error, but if averaged over a 1-second period much of this goes away). If I raise the device by 2 feet, the altimeter increases by 2 feet. No joke! This would be a hell of a lot better for measuring vertical gain than a GPS.

Problem is as I said above, no apps seem to use the barometer. Almost all "altimeter" apps just use the GPS (both inaccurate and imprecise. There are a couple pressure-measurement apps I found, but these don't have any useful tools for tracking altitude.

Anyone have anything to add to my quest for the perfect hiking toy?
-Jason Dorje Short

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Re: Phone Barometer/Altimeter

Postby GregMiller » Thu Apr 25, 2013 6:40 pm

I wonder if you could tie weather into it to automatically adjust for weather effects on pressure altitude.
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Re: Phone Barometer/Altimeter

Postby dsunwall » Thu Apr 25, 2013 8:10 pm

Garmin GPS's with barometers had an autocalibrate function that used GPS to work with the barometric pressure that somehow gave a pretty accurate altitude. I never completely understood how that worked. I doubt Garmin will release a smartphone app, although I see they do have some for pilots.

DS Altimeter app claims it works with barometers on phones, not sure what all it does. Glad to see smartphones adding the barometer, I'm sure usefull apps will follow. backcountry use for them keeps getting better.

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Re: Phone Barometer/Altimeter

Postby jdorje » Thu Apr 25, 2013 10:11 pm

There are a few Android barometer/altimeter apps, which I have tested to varying degrees. I may edit this if I find more (that are worth reviewing).

DS altimeter, Runtastic Altimeter, GPS Altimeter, Android Altimeter - may or may not include a barometer, but the altimeter on these apps just uses the GPS.

Barometer Monitor, Barometer and others - Include simple barometers. Some may show the altitude. Any app that does not include a QNH adjustment isn't worth looking at however. Android Sensor Box is worth mentioning because, though the barometer is extremely basic, it includes semi-interesting display for all sensors.

SyPressure is an interesting little app for monitoring pressure, however, it's geared toward weather rather than altitude. It appears to assume your altitude is constant and then predicts weather change based on the pressure. The pro version does include an altimeter but I have not tested it.

Barometer.WSK. Lets you "calibrate" the altitude by setting your current elevation and (?)temperature, but the calibration is not persistent.

Barometer and Altimeter is a far more technical app that probably mirrors an airplane's altimeter. By setting the QNH/QFE it does track your actual altitude (both AMSL and AGL). And if you don't know what those acronyms mean, you're screwed. On the up side, it has my altitude accurate to within just a few feet; it seems to load from a much larger database of ambient pressures than my toy app. It lacks any GPS integration (GPS is used to download the QNH), and being aviation-themed is probably more complicated than what a hiker would need. It has a widget, but this doesn't seem to display altitude. I cannot figure out what units it uses for QNH and QFE, but they certainly aren't the correct ones.

Barometer & Altimeter+DashClock. This grandly named fellow is very close to what I want in basic altimeter (no GPS use at all). Before starting, go into settings and change metres->feet, set the pressure range for the barometer spin wheel, and enter the 4-letter ICAO code for your nearest weather station (find a list here, i.e., KDEN for Denver). Scroll right to the altimeter. Up at the top you can reload the QNH (calibration) from that weather station, and you can also set the QNH by hand (essentially self-calibrating). It has a feature for recording elevations, which also tracks elevation gain, which I have not tested yet. Three problems: it lacks a widget that displays altitude, the QNH can only be set to the nearest millibar (~30 feet), and the output appears to be rounded off to the nearest metre (3+ feet) before being converted into feet. Ad-free.

----------

Also, the following is more than I ever wanted to know, but now that I know it, here goes. At reasonable altitudes, pressure drops by 1 mbar per 30 feet, meaning all calibration adjustments are basically linear. And if your barometer is accurate to .1 mbar, given the correct calibration adjustment you should know your altitude to 3 feet.

QNH = Q code; NH means nautical height. The QNH value is an adjustment for the ambient pressure, being the sea-level-adjusted pressure (mbar) for the current location and roughly equal to "pressure + altitude / 30". Putting this into your altimeter calibrates it for the current weather at your location.
QFE = FE means field elevation. This is the elevation of the local airport or ground (or maybe trailhead), so that when you land you get to 0. It lets you convert from AMSL to AGL. I think this is also given in millibars, so is a "pressure height", which means at reasonable altitudes you can just stick this into the altimeter in place of the QNH value and get your AGL height.
AMSL = above mean sea level
AGL = above ground level
WGS84 = GPS coordinates. Without an adjustment (via EGM84/EGM96/EGM2008), the GPS will ***not*** give you AMSL coordinates. Does not apply to barometric altimeters, but if you want a GPS altimeter you need that adjustment.

These Q codes are aviation related, where you know the pressure at certain benchmark locations (airports) and want to throw that data into your airplane altimeter to get an accurate elevation reading. The QNH value is sent via radio to the airplane. Hiking is a bit different in that we don't want the user to deal with the QNH value, but simply with altitude. If you enter the trailhead elevation, an app can then determine the QNH from the pressure at the trailhead, and will then be extremely accurate the rest of the way as to your altitude (until the weather changes). Carried further, this data can be applied to your GPS to greatly "smooth" the track it creates without introducing error (as described in an earlier post), though then you need to worry about the AMSL/WGS84 adjustment.

More to come.
Last edited by jdorje on Fri Apr 26, 2013 8:02 pm, edited 9 times in total.
-Jason Dorje Short

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Re: Phone Barometer/Altimeter

Postby dsunwall » Fri Apr 26, 2013 6:41 am

thanks for researching all that Jason, let us know when you find the right app or have one developed, by then I may be ready to upgrade my phone to one with a barometer.

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Re: Phone Barometer/Altimeter

Postby jeremy27 » Fri Apr 26, 2013 7:21 am

dsunwall wrote:thanks for researching all that Jason, let us know when you find the right app or have one developed, by then I may be ready to upgrade my phone to one with a barometer.

dsunwall,
In an earlier thread you mentioned you had a Galaxy S3 (and PMed me info regarding GPS apps). The S3 has a barometer - http://www.samsung.com/global/galaxys3/specifications.html. I just loaded the app recommended by Jason. It seems to be working just fine. I might go ride the elevator in my 30 story building later to see what happens.
-Jeremy

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Re: Phone Barometer/Altimeter

Postby dsunwall » Fri Apr 26, 2013 9:39 am

jeremy27 wrote:In an earlier thread you mentioned you had a Galaxy S3 (and PMed me info regarding GPS apps). The S3 has a barometer - http://www.samsung.com/global/galaxys3/specifications.html. I just loaded the app recommended by Jason. It seems to be working just fine. I might go ride the elevator in my 30 story building later to see what happens.
-Jeremy


wow, it appears nowhere in settings, (that I can find) thanks for letting me know, something new to try out this weekend.

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Re: Phone Barometer/Altimeter

Postby dsunwall » Fri Apr 26, 2013 2:57 pm

coming soon rugged Samsung S4 smart dudes there at Samsung, must be outdoorsy types.

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Re: Phone Barometer/Altimeter

Postby jdorje » Tue Apr 30, 2013 8:00 pm

The internet claims the s4 will have humidity and temperature sensors too. Perhaps I picked my phone too soon.

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