[lug] OT: android elevation app accuracy

Mon Sep 30 12:08:44 MDT 2013

There was a story on NPR about just that.  Apparently people have been
putting GPS jammers into their company vehicles so that they can go park
and take a nap or speed on the highway.  N. Korea was reported to have
done some rather heavy duty GPS jamming which did make aviation navigation
more difficult.

On Mon, 30 Sep 2013, Bear Giles wrote:

> I knew about the correlation stations but didn't realize averaging wasn't
> enough.
> 
> I wonder how they solved (or IF they solved) the concern about rogue
> stations that would broadcast signals to skew the results. It wouldn't
> really matter with survey gear but aircraft could get into trouble if the
> crew isn't paying close attention.
> 
> 
> 
> On Mon, Sep 30, 2013 at 11:59 AM, Quentin Hartman <qhartman at gmail.com>wrote:
> 
> > 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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> >
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