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Help, I need an education.

MVS 0 Points
edited April 2014 in Smartphone Navigation
This is crazy. I need to resolve an issue. I am about to invest my life in someone. We have been to Cancun together a few times in the last 1.5 years. Recently, she went to Cancun without me. 6 nights, 6 days. She decided to communicate with me via Facebook IM. We never communicated this way before. On the 4th day, I accidentially click on one of her messages and I realize that all the messages we sent each other are pinned using location services via GPS on our phones. I am ignorant to these technologies. I don't spent much time on FB. She has the newer Galaxy, I have the Iphone 5. Upon review of the last 4 days - she's where she is saying she is and supposed to be 90% of the time. On 2 different nights, however, it shows her at another hotel @ 15 miles away. God, the anxiety that came over me instantly. I cant overeact. I trust her, but I would be a fool to pretend I am not seeing her phone placed inside another hotel. So I confront her calmly. Neither of us can explain it. Although she makes a suggestion that we both were at the same hotel over a year ago and it possible something has a memory of past locations, and its some glitch in the system? I must tell you she has like a genius mind. Is this actually possible. I mean she is moving around at times -- always in the right place, (generally, the pin shifts slightly here and there -- but never miles) can it be possible the GPS hooks into another satellite with low signals with old records of locations? Another odd thing reviewing all the messages is that at certain times one minute she is at the right hotel and the next minute at the hotel 15 miles away. Can that be explained? I read somewhere yes -- that GPS updates every hour. True? I know this sounds crazy and I trust my girl -- but, I cant pretend this did not all just fall into my lap. I want answers if it possible understanding how GPS actually works. I am an odds, facts and statistics kind of guy - and it not adding up. Thank you for the feedback, sincerely, Anxious Joe.


  • nutcase 91 Points
    Dear Anxious:

    Here's a good website on how the satellite-based GPS system works:

    And here's a good primer on how cellphones can locate themselves using GPS and cellphone towers:

    There are also companies that map Wi-Fi networks around the world (e.g. SkyHook Wireless).

    The GPS receiver does not "hook[] into [a] satellite with low signals with old records of locations" since the satellites only broadcast (not record) data.

    However, a cellphone uses more than just the satellites to figure out where it is.

    If it can sense a cellphone tower, it can look up where that tower is located and know that it must be somewhere near there.

    If it can see (even if it cannot connect to) a Wi-Fi network, it can look at a database to find out where in the world that Wi-Fi network is.

    However, knowing the location of a cellphone tower or a Wi-Fi network isn't going to give the phone a precise location.

    Sorry I can't help you out with your personal concerns, but I hope the information above gives you some idea of how cellphone positioning works.
  • MVS 0 Points

    OK thank you. So in my case, I see the exact same location in 3 days back and forth from two different spots....15 miles apart from each other, statistics say the phone most likely is in that area?

    also, if moving in a car, from point a to point b..... can anything explain the location A at 11:50AM and location B at 11:51?

    Thank you. Again, Sincerely.
  • Tim 1500 Points
    GPS is accurate to within 10 meters, 95% of the time. GPS also does not work reliably indoors, so smartphones rely on augmentation systems (such as wifi positioning and cell tower triangulation) to determine location. How applications like FB then take that data and determine a location is entirely another matter.

    Someone I know moved from Hawaii to Maine. Their home wifi router had been added to a wifi positioning database (extremely common and routine) so when they moved to Maine their smartphone would always show them being in Hawaii when they were connected to their home wifi. It took nearly a year for it to figure out the correct new location.

    If your questions were simply about GPS, and GPS alone it would be much easier to answer. But you will never know how applications like FB use much less accurate and less reliable mechanisms (often not GPS) to determine your location.

    Applications like Facebook should never be used to prove or disprove that someone was or was not in a particular place at a particular time. They are not reliable for that.
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