Location issue?Support


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  1. shantytownbrown

    shantytownbrown Well-Known Member This Topic's Starter

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  2. marctronixx

    marctronixx Moderator Moderator

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    carrier based aGPS is nto as accurate as satellite based GPS. its the nature of the beast. the mobile phone towers can approximate where you are based on triangulation (which im sure you know this). if your handset can not see any GPS birds LOS (Line Of Sight) then it reverts to cell/wifi(if available) triangulation.

    now seeing as your location is miles off is not commonly reported but does not mean it does not happen...

    are you going outside and letting the birds (GPS antennas in the sky) see you?

    smoke over this thread:

    http://androidforums.com/htc-evo-4g/148228-how-good-your-gps.html

    install that app and see how many birds your handset can see.
     
  3. shantytownbrown

    shantytownbrown Well-Known Member This Topic's Starter

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    I am seeing 10 out 10 max at 10ft accuracy....

    how does that affect my cell tower innacuracy?
     
  4. EarlyMon

    EarlyMon The PearlyMon Moderator

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    I've read that other thread twice and I'm still not sure what you're looking for.

    If you're trying to improve your tower accuracy, I do not think that's possible.

    The tower location is a good approximation, usually, but so long as gets your aGPS properly assisted, and you're ending up with 10' location accuracy, then what's the problem?
     
  5. shantytownbrown

    shantytownbrown Well-Known Member This Topic's Starter

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    I will try to be clearer...

    with GPS off my maps program and weather program thinks i am 4 or so miles to the northeast of where i really am. I assume it is triangulating my location with cell towers...(no???)

    with gps on, everything point to the roof of my home...

    why the discrepancy...

    talk to me as if i am in second grade, i dont know too much about how this stuff works....
     
  6. EarlyMon

    EarlyMon The PearlyMon Moderator

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    Ok. Imagine you are in between two radio transmitters so that you and the two are in straight line. Imagine that they send out a signal at precisely the same time. Imagine that you receive those signals at precisely the same time.

    For that to happen you would have to exactly halfway between the two antennas. If we knew where those transmitters were, we'd know precisely where you were.

    Using the arrival times, we could calculate your exact location anywhere along that line.

    Now, let's add a third transmitter, not on the line - the three form a triangle. You can move anywhere in that triangle and using the same signal-arrival-time math, we could precisely locate you. That's triangulation. To work requires the highest precision time, radios, and knowledge of the transmitters' location.

    GPS has that precision, cell towers do not.

    With GPS, that translates to closely getting your position right no matter where you go.

    With cell towers, the approximation of your location varies as you move about within the network, making it more luck of the draw.

    Does that help?
     
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  7. shantytownbrown

    shantytownbrown Well-Known Member This Topic's Starter

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    ok, so i understand the concept, however, is "less accurate" [the cell towers] miles vs feet? that just doesnt seem "normal" maybe it can be...do tell me if in some situations i could expect that...

    if not, is there anyway to correct this...?
     
  8. EarlyMon

    EarlyMon The PearlyMon Moderator

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    From:

    Sprint - FAQs[FAQs]

    The error term will depend upon where in the country you're located - and cannot be corrected.

    The original intent of the cell tower location is to foreshorten GPS position acquisition (the whole aGPS thing) and then they added to augment GPS positioning when you don't have ideal GPS signal reception.

    That's my understanding.
     
  9. shantytownbrown

    shantytownbrown Well-Known Member This Topic's Starter

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    So last nite i looked at my wife's EVO...It pointed her to within 1/4 mile of our home...so I looked at mine...same...!!! fixed I thought....maybe google "learned"???

    then...this morning...mine back to 4 miles away! her's down the street 1/2 mile or less...

    same settings, her GPS is off as well...

    sorry, just don't get it...

    UPDATE: just a few minutes later, now i am getting the same location as wife's phone...

    still confused...
     
  10. kamikazekyle

    kamikazekyle Well-Known Member

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    Cell tower triangulation is not very precise the majority of the time. It can vary, even between cell phones sitting next to one another. This is why your wife's phone can show one location via triangulation and yours another (it also has to do with tower location and time). Once the triangulation is done, your weather app then "rounds" your location to the nearest weather location in the database, and then gives you that weather.

    For reference, my average in-city triangulation variance for my area is 1.5 km radius. Out near my girlfriends house where cell phones are still struggling to be adopted, I'm hit around 6km accuracy. At her house, Google Maps can put me several miles north, closer to the nearest Sprint tower. While on vacation, Beautiful Widgets liked to approximate my location in the middle of the Atlantic.

    So, in short, tower triangulation is a relative crap shoot for precision and very dependent on the location and distance of towers and the alignment of the moons. There's also no real way to improve it by settings or the like.
     
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  11. EarlyMon

    EarlyMon The PearlyMon Moderator

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    OK - I was trying to avoid the too-much tech - but it's all about the timing - and perhaps a little of what we call multipath.

    GPS timing accuracy: First and foremost - GPS satellites are all sending the same information - they're aware of each other - and the details of their timing accuracy are classified (GPS was originally built for the Department of Defense). All I'm at liberty to say is that each satellite is in as perfect as technically possible synchronization with every other satellite - they all agree on the exact same time - and the time is insanely accurate by any measure. (I worked on a piece of GPS in an earlier part of my career, so this isn't re-hased info I'm tossing out.)

    GPS satellite flight: The satellites are stationed in half-geosynchronous orbit. Unlike a communications satellite or satellite TV that appear stationary in the sky - each GPS sat orbits mother earth twice a day. There are a few reasons for this - but only one I'll toss out here: while you theoretically need three sources for triangulation, with GPS you'll get multiples and your receiver's intelligence can choose for best signal quality of those available in the sky - because of atmospheric effects and maybe a few other factors, not all signals from all visible satellites will arrive to you equal in quality. Remember, even though we're talking digital signals - we care about time and we care about time of arrival. The better skyview you have, the better your accuracy - the signal is hitting your receiver directly.

    Tower timing: close enough to coordinate with other towers and lock-on to talk/listen to phones - that's it. No more.

    Tower signal: can be affected by any number of terrestrial or man-made effects - interference, you name it.

    Tower accuracy: for location, signaling, timing - good enough for phone calls, not deploying anywhere near the accuracy of satellites. Calibration performed as needed/scheduled, not _closely monitored_ in real-time by the Department of Defense.

    Why does your tower accuracy vary by time of day and by phone? Terrestrial, calibration, or man-made effects are in play.

    Call your wife's cell while you stand right next to her - listen to the delay. Do the same to various landlines. Lots of variance there due to telecommunications switching - and the nature of terrestrial-based signals.

    If you gave the job of tower location to the Department of Defense, they'd solve every single aspect of this task - and they'd put the towers in orbit.

    If you consider that a radio wave in the atmosphere is kinda traveling near the speed of light - 186,000 miles/second - and then consider that you're ONLY bouncing around from a 1/4 mile to a few miles in location accuracy, you'll appreciate just how very close the timing accuracy of the cell towers already is.

    A four mile error can be roughly expressed as being 22 millionths of a second off. Not bad when you think of it that way.

    Your phone's ok, the cell network is ok, if you want location accuracy and stability - you simply want GPS.

    Does this help any?

    If interested, see also -

    http://en.wikipedia.org/wiki/Global_Positioning_System#Basic_concept_of_GPS
     
  12. shantytownbrown

    shantytownbrown Well-Known Member This Topic's Starter

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    @EarlyMon....

    excellent dissertation.(no sacasm intended) i get it now..thanks for putting in the effort to post...

    ( i think i understand at more than the second grade level...lol)

    again, many thanks
    also thanks to kamikazekyle...
     
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