[lug] OT: android elevation app accuracy

Mon Sep 30 11:59:00 MDT 2013

I'm sure there are some apps that will do averaging, but that's not
terribly useful for survey-grade precision. Most of the accuracy that is
present in professional-grade GPS gear comes from a correction signal they
get from a basestation that has a known fixed location. When I worked for
the University of Oregon I had some exposure to this stuff while I was
working on mapping our underground telecom infrastructure. It was neat
stuff, but ridiculously expensive. Some more info:

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

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

QH

On Mon, Sep 30, 2013 at 11:43 AM, Bear Giles <bgiles at coyotesong.com> wrote:

> 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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>>
>>
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>
>
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