It works well below deck when you are in cell range. How does it work below deck with just a GPS signal offshore? I don't want to belabor the point. Jerry
Sent from my iPhone > On Oct 2, 2015, at 4:36 PM, Graham Collins via CnC-List > <cnc-list@cnc-list.com> wrote: > > Hi Jerome > I must disagree with that statement. My sony tablet with built in GPS works > perfectly below decks, it is what I use for anchor watch. > Graham Collins > Secret Plans > C&C 35-III #11 >> On 2015-10-02 12:42 PM, Jerome Tauber via CnC-List wrote: >> Joe - that is a common misunderstanding. While the Iphone does not need >> cell service for positioning it actually does use cell tower triangulation >> for position and is not very accurate or fast without it. Moreover, if you >> are below deck you will not get an adequate GPS signal. This is from the >> internet. >> MotionX-GPS >> >> Does MotionX-GPS require a cellular network? >> >> The iPhone 5, 4S, 4, 3GS and 3G use an A-GPS (Assisted-GPS) chipset which >> uses cell tower triangulation to speed up GPS signal acquisition. Cellular >> coverage is not needed to acquire a signal, however the signal acquisition >> will be much quicker if you have data coverage. >> Without data services, it can take 15 minutes or longer to acquire a signal. >> This is simply because it takes longer to determine which satellites to use >> out of the 31 available around the world. With data services, it typically >> takes under a minute, but it can take up to 5 minutes. >> >> How the iPhone knows where you are >> >> By Glenn Fleishman, Macworld >> iPhone users' experience with GPS is so quick, so instant-on, that Apple's >> Wednesday response about location tracking on iOS might almost seem baffling: >> Calculating a phone’s location using just GPS satellite data can take up to >> several minutes. iPhone can reduce this time to just a few seconds by using >> Wi-Fi hotspot and cell tower data to quickly find GPS satellites. >> Several minutes? Doesn't my iPhone take just seconds to figure out where I >> am? >> Well, yes… but only when it engages in a set of tricks to avoid a lengthy >> process that was de rigueur when GPS receivers first appeared. >> In simplifying matters, Apple’s not being entirely accurate about how this >> all works and what it's doing. So let me explain where Wi-Fi and cell phone >> towers fit into the equation. >> 12.5 minutes to locate >> >> Early GPS receivers took 12.5 minutes from a cold start to obtain a lock; >> later locks in the same region could still take minutes. If you turned a GPS >> receiver off for a few weeks or moved it more than a few hundred miles, a >> cold start might be required again. >> GPS relies on two factors to create a set of accurate coordinates for where >> you’re standing: time and space. GPS satellites broadcast precise time >> signals using a built-in atomic clock along with their current location. >> They also broadcast the location of all other satellites in the sky, called >> the almanac. >> Every 30 seconds, a GPS satellite broadcasts a time stamp, its current >> location and some less precise location information for other >> GPS satellites. It takes 25 of these broadcasts (thus, 12.5 minutes) to >> obtain the full list of satellite locations. This information has to be >> decoded for a receiver to then properly interpret signals from the >> satellites that are within range. >> If you know the position of four satellites and the time at which each sent >> their position information, you—or, rather, your GPS receiver—can calculate >> to within 10 meters the latitude, longitude, and elevation of your current >> location along with the exact current time. With three satellites, you lose >> elevation, but a device can still track movement fairly accurately. >> Standalone GPS receivers can lock in simultaneously on multiple satellites, >> and track more than four. Other techniques can improve accuracy, too. >> But, heck, I don’t have 12.5 minutes. I’m a busy man! Give me that location >> faster! >> Giving GPS an assist >> >> So GPS chip and gear makers came up with a host of ways to shorten the wait, >> called Assisted GPS (AGPS). Instead of relying on live downloads of position >> data from satellites, future locations can be estimated accurately enough to >> figure out rough satellite positions, and get a fix at which point even more >> up-to-date information is retrieved. These estimates can be downloaded via a >> network connection in seconds or even calculated right on a device. >> The current time can also be used as a clue. With a precise current time, >> fragmentary satellite data can be decoded to gain a faster lock or figure >> out the appropriate information to use. In CDMA networks, such as that used >> by Verizon, GPS-synchronized atomic time is required for the network’s basic >> operations, making it a simple matter to have such information available. >> (In fact, CDMA cell towers have GPS units built in to maintain better atomic >> time synchronization.)These extras are what makes GPS into >> AGPS. Though a lot of people misunderstand AGPS and think it’s some faux GPS >> system, that’s not the case: AGPS requires a GPS receiver to work. Apple’s >> iPhone and 3G iPad models include AGPS, as do nearly all competing devices >> with GPS chips, notably Android phones. (AGPS allows the use of much cheaper >> and simpler GPS circuits in phones, reducing cost and battery drain.) >> >> This is where Apple’s statement on Wednesday deviates from full accuracy. >> Apple uses AGPS for native GPS-lock improvements, and Wi-Fi network and cell >> tower locations are additional factors in providing a fast initial >> connection along with improving GPS accuracy. >> Cellular carriers have extremely precise GPS measurements of the locations >> of all their towers. With a database of such towers, you can take >> measurements of the signal strength of those within range—which may be >> dozens—and trilaterate to find an area that overlaps among them. >> (Trilateration involves overlapping regions to find an intersecting area; >> triangulation uses the measurement of angles to find a center point.) >> But cell towers are too far away from one another to provide GPS-like >> precision, and they don’t work well in less-populated areas, even suburbs, >> where less coverage is necessary than in an urban environment. >> >> >> _______________________________________________ >> >> Email address: >> CnC-List@cnc-list.com >> To change your list preferences, including unsubscribing -- go to the bottom >> of page at: >> http://cnc-list.com/mailman/listinfo/cnc-list_cnc-list.com >> > > _______________________________________________ > > Email address: > CnC-List@cnc-list.com > To change your list preferences, including unsubscribing -- go to the bottom > of page at: > http://cnc-list.com/mailman/listinfo/cnc-list_cnc-list.com >
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