[lug] OT: android elevation app accuracy

[Quentin Hartman]

I've done some experimenting w/ altitude measurements on my android
devices, and the most precision I got was a couple feet. I imagine though
that those are GPS-based measurements rather than an actual digital
barometer.

I really doubt that anything included in a phone would give you the
resolution you need. If the water-level technique really won't work (I've
used water levels for similar tasks, it required a lot of hose, but was
doable) then your best bet is probably to rent or borrow some surveying
equipment and taking the measurements that way. Modern transits are pretty
automagical, so even with no experience at all I bet you get get a very
precise measurement in just a few minutes. Even with old school equipment
once you have your fixed points, a small bit of trig will get you there.

QH


On Mon, Sep 30, 2013 at 9:03 AM, Davide Del Vento <
davide.del.vento at gmail.com> wrote:

> Thanks for all these suggested (which of course I knew already, being
> a physicist by training.
>
> They are all very unpractical for what I need to do, because the
> corners are opposite and not in sight, the gutter is not level (and
> has a large "gap") and there is lots of additional small tricky
> details. The only feasible technique would be the bucket with the
> hose, but by no means easy or quick.
>
> Regarding the joke, that was probably true in the old times, but now
> things are different. Air pressure is about 84kPa at our altitude and
> here there is a differential of about 1kPa every 100m (330 ft).
>
> A barometer such as this http://www.omega.com/pptst/HHP360.html claims
> to be able to measure 0.015% or 0.01kPa or 1m (3ft) of ABSOLUTE
> pressure. So it can certainly measure the height of a building even if
> it's not as tall as a skyscraper! It can't go down to inches as
> absolute pressure, but maybe it can go there for relative one, which
> is what I need. However it's too expensive to try (or even spending
> time reading its specs to understand).
>
> According to http://what-if.xkcd.com/64/ an Android device is able to
> measure the pressure difference between head and feet of a person, so
> that's why I asked here in the first place: maybe it can measure an
> inch. Has anybody tried?
>
> Thanks!
> Davide
>
> On Sun, Sep 29, 2013 at 4:48 PM, Bear Giles <bgiles at coyotesong.com> wrote:
> > Actually I just remembered a second approach. If you can run a hose
> between
> > two buckets of water you can use it as a level. You'll need to make sure
> > that the hose is completely full so the water can freely flow between the
> > buckets but other than that it's a matter of putting the buckets on each
> > corner of the building and figuring out a way to measure the height of
> the
> > water to what you're trying to check.
> >
> >
> > On Sun, Sep 29, 2013 at 4:40 PM, Bear Giles <bgiles at coyotesong.com>
> wrote:
> >>
> >> This reminds me of the old physics major joke about how you determine
> the
> >> height of a skyscraper with a barometer.
> >>
> >> A: find the building super and tell him you have a neat barometer for
> him
> >> if he tells you the height of the building.
> >>
> >> You'll need a level. A barometer isn't going to cut it, not even
> remotely.
> >>
> >>
> >> On Sun, Sep 29, 2013 at 4:35 PM, Jed S. Baer <blug at jbaer.cotse.net>
> wrote:
> >>>
> >>> On Sun, 29 Sep 2013 16:28:03 -0600
> >>> Jed S. Baer wrote:
> >>>
> >>> > > i.e. how much slope there is, if any,
> >>> > > between these two corners
> >>> >
> >>> > I think your best bet will be to use a string level. Or, a 4 foot or
> >>> > longer beam level, working along your gutter.
> >>>
> >>> Or,
> >>>
> >>>
> http://www.homedepot.com/p/Johnson-Hand-Held-Sight-Level-80-5556/202911589
> >>>
> http://www.homedepot.com/p/Johnson-Torpedo-Laser-Level-40-0915/202258085
> >>>
> >>> Might be you know someone who has a laser level already?
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> >>
> >
> >
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