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Does the iPhone actually have real GPS, or is it just based on 3G towers?

• jessedhillon 16y ago
  It has A-GPS, which is inferior in some ways to true GPS, but is much more accurate than triangulating from towers (which it will resort to under certain conditions.) http://en.wikipedia.org/wiki/List_of_devices_with_Assisted_GPS http://en.wikipedia.org/wiki/List_of_devices_with_Assisted_G...
  • tienshiao 16y ago
    The iPhone (3G, 3GS, and 4) and the 3G iPads have fully functional GPS hardware, and also use A-GPS to acquire a position fix. If you've ever used a normal standalone GPS in one city and gotten on a plane and flown across the country and tried to use the GPS again, you'll know that it can take 5+ minutes to reacquire a fix that first time off the plane.
    • ugh 16y ago
      Assisted GPS seems to be a very poor choice of name. I have repeatedly met people who wrongly believe that Assisted GPS is not actual GPS.
      • jessedhillon 16y ago
        Some AGPS devices cannot determine their own position from a satellite signal, whereas others can as long as they have received an almanac from a server in the recent past. It depends what you mean by "actual GPS". Some implementations are completely incapable of acting in a standalone capacity.
        • ugh 16y ago
          Here is what the Wikipedia article you linked to says: "Standalone" or "Autonomous" GPS operation use radio signals from satellites alone. A-GPS additionally uses … Wrong?
          • jessedhillon 16y ago
            I don't see how this contradicts what I said, which is that some AGPS implementations require assistance in order to accurately determine your location. Not every AGPS device can map radio signals to a lat-long; some can only do that with assistance. It also lists some ways that various implementations require assistance: Assistance falls into two categories: Information used to more quickly acquire satellites It can supply orbital data or almanac for the GPS satellites to the GPS receiver, enabling the GPS receiver to lock to the satellites more rapidly in some cases. The network can provide precise time. The device captures a snapshot of the GPS signal, with approximate time, for the server to later process into a position. Accurate, surveyed coordinates for the cell site towers allow better knowledge of local ionospheric conditions and other conditions affecting the GPS signal than the GPS receiver alone, enabling more precise calculation of position. (See also Wide Area Augmentation System and CellHunter and openBmap.) Calculation of position by the server using information from the GPS receiver The assistance server has a good satellite signal, and plentiful computation power, so it can compare fragmentary signals relayed to it
            • ugh 16y ago
              That’s not what the article says. It says that AGPS devices are just like GPS devices. The only difference is that they use additional information to improve startup times. Assistance is described as something that’s entirely optional. Why do you think that’s not the case? I googled around for a bit and it seems as though every source I can find tells me that AGPS is just like GPS if you have no data connection.
              • jessedhillon 16y ago
                I'm sorry but I don't know how to make it more clear than I already said before: some AGPS implementations are not capable of operating in standalone mode. The Wikipedia A-GPS article states: A typical A-GPS-enabled receiver will use a data connection (Internet or other) to contact the assistance server for aGPS information. If it also has functioning autonomous GPS, it may use standalone GPS, which is sometimes slower on time to first fix, but does not depend on the network, and therefore can work beyond network range, and without incurring data usage fees.[3] Some aGPS devices do not have the option of falling back to standalone or autonomous GPS. I've added emphasis. The last point is all I was saying.
  • asmosoinio 16y ago
    Inferior in what ways? My understanding is totally opposite, would you mind explaining a bit more?
    • blastek 16y ago
      It is better. He has no idea what he's talking about.
      • jessedhillon 16y ago
        Actually I do. I answered the question on sibling posts.
  • nl 16y ago
    Assisted GPS is better than normal GPS. It uses towers to work out how to find the GPS satellites quicker than normal, and additionally can provide some location information when no GPS is available.
    • jessedhillon 16y ago
      > Assisted GPS is better than normal GPS. Really? My Garmin device can locate itself without entailing the possibility of communicating my position to a third-party. There is no possibility that my checking my position can enable anyone else to know it as well. That's not true with AGPS. That is one pretty significant way that standalone is superior.
      • nl 16y ago
        That is one pretty significant way that standalone is superior. Maybe. The majority of people just want to know where they are and the quicker the better.
      • ugh 16y ago
        If that’s important to you, sure. I’m, however, a bit foggy on the actual implementation of AGPS and don’t really know whether it actually sends your location info to a server. Would be nice to get some implementation details about that. I think it was pretty clear that we were talking about performance – time until and precision of the first lock (which AGPS does improve), overall precision (which AGPS doesn’t improve) and so on.