[lug] OT: android elevation app accuracy

Mon Sep 30 11:43:52 MDT 2013

GPS elevation is less accurate than GPS position, at least for (most)
consumer-level gear. It makes sense since you usually don't care about
elevation as much as long-lat. You're on the ground. 'nuf said.

(That's also why they strongly state you shouldn't use them for aviation.)

Related question - are the mobile phone apps that will do the averaging for
you? Just put the phone on a table outside for a few hours and get a much
more accurate position. (I Know survey equipment can do this.)

I've accidently left my GPS watch recording after a run and it's fun to
look at the starburst as the calculated position roams around.

On Mon, Sep 30, 2013 at 11:37 AM, Quentin Hartman <qhartman at gmail.com>wrote:

> 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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