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post #11 of 21 Old 07-14-2009
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Not true at all. AGPS is an improvement over just GPS, doesn't need a data connection unless the satellites aren't available for whatever reason. There should be no extorting data here unless you have a "no data" plan. Here is the excerpt from Apple's site:

GPS (Global Positioning System) technology uses information from earth-orbiting satellites to find locations. A-GPS (Assisted GPS) on iPhone 3G goes a step further, finding the closest satellites to more quickly identify your position. If you’re not within a clear line of sight to a GPS satellite, iPhone finds you via Wi-Fi. If you’re not in range of a Wi-Fi hotspot, iPhone finds you using cellular towers. The size of a location circle tells you how accurately iPhone is able to calculate that location: The smaller the circle, the more accurate the location.
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post #12 of 21 Old 07-14-2009
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Apple has said they have "agps" which means "assisted GPS" which in turn means it doesn't work without a data network connection. "agps" phones receive the gps satellite signal but are incapable of processing it. Or so I've been told.
As I understand it, the assist does use the data connection to go out and query info about the tower(s) you are connected to when you first start up the GPS, it then sends those coordinates to the GPS receiver and tells it that is where you are. The receiver then goes and gets a fix like normal, but is speeded up because it already has a pretty good idea where you are on the globe to start with.

Most auto GPS units (and my chartplotter) do something similar in that they store the last known position in memory and use that as the starting point the next time they are turned on.

so in short, if you don't have data service the gps unit should still be able to function in normal mode, but it could take 20-30 minutes to get a lock (I've heard of some samsung blackjack II's taking up to 45 minutes to get a lock when the assist was turned off, but less than 30 seconds with it enabled).

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post #13 of 21 Old 07-14-2009
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Graeme, in the US the carriers will sell you "agps" nav plans for $10 per month. Without that plan--you can't use the apgs feature in the phones. There's no way to access the gps capabilities. As opposed to phones (mainly not available in the US except from Sprint/Nextel) which actually have on-board GPS that can be used stand-alone.

If Apple or someone else has redefined how they are using the feature, or what they are calling it, that's just "newspeak".

By and large? An "agps" cell phone in the US is just a brick, if you are in the woods or at sea out of range of the nearest cell towers. It is not simply 'assisted' it is "requires the assistance of". The phone only contains a GPS receiver, it is unable to compute the position form the signals it obtains. The cell phone system does the computation and then returns the result to the phone, so the "assistance" is mandatory.

Clever way to force users to pay an extra ten bucks a month, instead of just looking at their phones.
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post #14 of 21 Old 07-14-2009
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That's quite interesting, I've yet to hear that here in Canada but they do try to sell data plans which just make sense to have with a 3G equipped phone.

I'm not entirely sure that the GPS doesn't work without the towers because when we were sailing around it was able to figure out where we were despite having no reception in certain spots. Granted it was a bit slower to find us (I think..) it still managed to do it. I'm definitely going to look into that more though, thanks for the info.

Here we have two carriers, Fido and Rogers (same company though) and you can't buy a phone from one and use it with the other. Which in turn makes me think that the carriers are adjusting the OS of the phone itself to turn off the GPS abilities if you don't pay the extortion fee? That sounds harsh but completely reasonable from what I understand of how north american cell phone carriers work (compared to other countries like Japan for example).
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post #15 of 21 Old 07-14-2009
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Quote:
Originally Posted by hellosailor View Post
Without that plan--you can't use the apgs feature in the phones. There's no way to access the gps capabilities. As opposed to phones (mainly not available in the US except from Sprint/Nextel) which actually have on-board GPS that can be used stand-alone...
That is generally false. I (and many others I know) have never once paid for the cell companies GPS service on any cell phone, and I frequently use the GPS features on my current, and previous phones.

What is correct is that AT&T (and probably other carriers as well) does try to block the GPS unit on some units within the phone software so that it will only work with their telenav software (BlackJack II with windows mobile 6 was locked) and sometimes require a hack to access the GPS unit from programs like google maps or Live, (the windows mobile 6.1 software update, on the same exact phone, required no hack and the gps would work with any program)

From Wikipedia Assisted GPS article:
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A typical A-GPS-enabled cell phone will use a data connection (internet, or other) to contact the assistance server or a standard network connection for A-GPS information. If it also has functioning autonomous or standalone GPS, it may use standard GPS, which is sometimes slower on Time To First Fix, but does not lead to network dependent downsides, such as failure to work outside of network range, or charges for data traffic.[3] Some A-GPS solutions do not have the option of falling back to standalone or autonomous GPS.

You are correct that without a data connection to the cellular network (it uses the cell tower to determine it's starting position) the "assist" feature will not function on the A-GPS receiver, but virtually all gps unites in phones are of the type that features a standalone receiver as well, and while they may take a long time (I've personally seen 30+ minutes, and heard of 45+ minutes in extreme cases with weak signals) to get the initial lock without the assist, they will still get the lock, and once done, they will operate as any other GPS unit.

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post #16 of 21 Old 08-10-2009
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True, iPhone become quietly quite a navigation device. Cheap Navionics charts and quite good iNavX software. It's doing even AIS now!!! Also real-time chart plotting, it supports waypoints & routes including KML (Google Earth) and GPX import/export, track log, measuring bearing/distance, GRIB weather forecast, tides/currents

iPhone – one of the best sailing gadgets ever ę Sailing Gadgets

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Last edited by jaakennuste; 08-10-2009 at 10:19 AM.
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post #17 of 21 Old 08-10-2009
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I stand corrected about A-GPS. Just recently read an article that explained it actually comes in FOUR flavors. In the best of these, there is a full GPS chip in the phone and it is assisted by the cellular network to enhance the position results, i.e. using tower triangulation when there is no sky view.

In the worst of these modes, the phone only contains 1/2 of a GPS chip, and can't even compute a position (let alone reveal it to the user) without the assistance of the network. Sadly this is what the US carriers have mainly done, our typical A-GPS phones can't be used except by paying an extra $10/month for "navigator" services. (Nextel/Boost being the big exception, but they're tiny players in the market.)

I haven't been able to get a clear reply from AT&T or Apple, but it sounds like the iPhone includes unlocked AGPS, i.e. that the GPS in the phone can be used while off the network, without extra charge. Although, of course, you can't get the phone without a data plan ($30/month extra?) so the carrier is getting their dime one way or the other.
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post #18 of 21 Old 08-27-2009
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Send a message via Skype™ to LydiaD
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I realize this is an old thread but I wanted to make sure you all know this if you have the app and tried to update it recently.

Last week Navionics uploaded the newest version of the app (3.0) to iTunes. There was a bug in the upload that caused several regions to display incorrectly and were subsequently removed from iTunes. We apologize for any inconvenience!

More information about the regions affected and the new version can be found on our web site. http://www.navionics.com/MobileMarineFeatures.asp

Today, version 3.1 is live on iTunes. If you tried to download the 3.0 update and it failed, you can now get 3.1. Of course, itís a free update.

Version 3.1 has a new feature that many of you have been asking for. You can now input a lat/long directly and go to that point on the chart. You can still send those via email to anyone else etc. and add them to Google Earth.

Lydia/Navionics CS Manager

Last edited by LydiaD; 08-27-2009 at 03:21 PM.
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post #19 of 21 Old 08-28-2009
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Quote:
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why not just download the already calibrated charts from NOAA, for free? They are also going to be more up to date than the paper ones you purchased and scanned...

NOAA Raster Navigational Charts

edit: the URL won't save correctly because of the tag at the end, so I changed it to a tinyurl
I doubt NOAA has charts for my region at GMT +8.00hrs

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post #20 of 21 Old 08-28-2009
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I doubt NOAA has charts for my region at GMT +8.00hrs
heh, no... looks like the closest they get is the Mariana islands, which is GMT +10

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