[ampere]

Originally Posted by praful

With a AGPS you are already connected to the Mobile tower and just the information needs to be downloaded, hence it is faster to get a lock.

With a standalone it first connects to the satellites and then downloads the location data and is slower. But it is far far more accurate than a AGPS. Some phone have both AGPS and GPS, i.e. they get a initial lock using AGPS and then further get a accurate lock via the GPS receiver.

Which means that AGPS is not just a cell tower based location finder. It just uses the cell tower to lock to the position faster. But it still uses the satellite. In other words, it still has a GPS RX in the phone.

In that case it should work, even if there is not network, by locking on to the satellites through the regular procedure (with using the cell tower info).

[salbin]

Originally Posted by Technocrat

Simply put a device with a GPS receiver will work even if there is no network while the one which does not have it will not.

Yes.
That is what I use.
It is satguide navigation software installed on Asus P320 (windows mobile).
No worry about the GPRS data transfer and mobile networks
Most of the time it gives an accuracy of within 20m.
All India map with Destinator software costs ~Rs.2200.
Single state maps are still cheaper @ around Rs.1000.
Satguide has got softwares for Symbian OS also.
Those who does not have in-built GPS receiver can get "Go GPS Kit" external receiver and pair it with the phone using bluetooth and use the same navigation software (around Rs.4000).
MapmyIndia also has got similar softwares in the same price range, but I have not used it. So no comments
Here is the photograph of my set-up:

[skdking]

Let us come back to the original point.

I have a postpaid BSNL 3G connection.

In my E72 I have got pre-loaded Ovi Map (updated by me from time to time). Since usage of Ovi is free now I do not have to spend anything if I stay offline.

I have also loaded Google Map into my phone as it is more content rich and easy to use. But Google Map tries to hook on to net whenever I am out of the cached area and attempt to connect to it. This leads to 3G charges.

My query is that is there some way by which I can download Google map's database via my PC, like Ovi Map, and load it to my mobile so that I can connect to Google Map while remaining offline.

[praful]

Originally Posted by Technocrat

Praful by that definition phones with AGPS would not latch on to the satellites right?

Can any Nokia 5230 owners confirm this i.e. whether it uses satellites for navigation or not?

Phones with 'only' AGPS would not be latching onto satellites, the cell towers would be doing that!

Originally Posted by ampere

Which means that AGPS is not just a cell tower based location finder. It just uses the cell tower to lock to the position faster. But it still uses the satellite. In other words, it still has a GPS RX in the phone.

In that case it should work, even if there is not network, by locking on to the satellites through the regular procedure (with using the cell tower info).

Again, most of the AGPS phones in the market are AGPS only and not AGPS+GPS Rx. So they would fail to work in a no network zone.

[Technocrat]

Praful the doubt is how does one know? Most of the phones which do triangulation & that I know of, do not mention AGPS or any such thing yet can show one's location on gmaps.

Now we have phones like Nokia 5230 which mentions AGPS & so far most of us are under impression that it has GPS.

So can Nokia 5230 users confirm if their phone is only AGPS or A+GPS?

[tsk1979]

AGPS has nothing to do with location. AGPS is just a map of the sky, which is given to GPS receiver. The reason for this is that if GPS chip knows where the satellites are, fix is quick. Otherwise, it needs to do a cold fix, which can take 2-3 minutes if signal is not strong.
However, on GSM phones, using tower triangulation, rough location can be determined. Thats using cellphone towers, and signal is necessary for that.
However, for GPS operation, no network is needed.

[Technocrat]

Thanks for the info Tanveer.

So AGPS too would work without a network right?

[santosh.s]

From what I know, positioning based on only GSM towers is called "cell-id". On map display it shows location as circle with about 1km radius, indicating you are somewhere within that area. A-GPS is used to speed up initial locking of usual GPS with satellites as others have explained. I believe it needs GSM network (and probably internet too, not sure) through which it works. So, I guess "only A-GPS without GPS" doesn't really make sense. A-GPS should imply presence of GPS hardware otherwise what else will it "assist"?

[tsk1979]

Originally Posted by Technocrat

Thanks for the info Tanveer.

So AGPS too would work without a network right?

Nope, How do you download the map of the sky if you got no network

[sanjayc]

Originally Posted by Technocrat

Thanks for the info Tanveer.

So AGPS too would work without a network right?

Nope, AGPS cannot work without network, since it has to talk to the service provider server for getting additional info (that is why A is for assisted), which includes tower location, current time etc.

http://www.intomobile.com/2007/06/21...assisting.html

"The A in AGPS stands for assisted. Your mobile takes a snapshot of what current satellites are visible and talks to a server that knows where the closest cell phone towers are. The server calculates your exact location and spits it back out to your device. "

There are other type of "assisted" technologies as well..more info here Assisted GPS - Wikipedia, the free encyclopedia

[Technocrat]

Ok so a device which advertises AGPS feature would work uses assist for quick locking when in network would be only GPS & not AGPS when not in network?

Like Sanjay said earlier if AGPS is only based on cell-id then its nothing but marketing gimmick by Phone maker.

[sanjayc]

Originally Posted by Technocrat

Ok so a device which advertises AGPS feature would work uses assist for quick locking when in network would be only GPS & not AGPS when not in network?

Like Sanjay said earlier if AGPS is only based on cell-id then its nothing but marketing gimmick by Phone maker.

Think of it like this..AGPS can be enabled on any GPS-enabled cellphone via a firmware/software upgrade, since "Assisted" function is a software function. Nokia N95 is a prime example..during its launch period getting a gps fix was a nightmare but post the firmware upgrade it is damn quick.

AGPS requires network connection and sometimes internet connection as well depending on the service provider and package bundling.

AGPS will work where pure GPS may not (provided network coverage is avlbl). For example, in my iPhone, if I am using google maps, it will show my location inside my residence (using AGPS+integration with iPhone OS) but MapMyIndia software will not until I am in the open.

As per my understanding goes, with AGPS, the mobile sends the information of nearest cell tower and current time to the server. On the server, data regarding satellite positions are continuously avlbl and updated. This position is transmitted back to the mobile which now gets the appx long/lat co-ordinates from the server instead of the in-built gps receiver..over some minutes, if the inbuilt-gps is able to get a fix, this coords gets updated.

Bottomline is, pure GPS will give the best/accurate location in favourable conditions (under open sky,that is any place on earth) but will take some time, whereas AGPS will always give a near-approximation (which will vary based on distance from tower) almost instantly under all conditions with network coverage avlbl.

[salbin]

Is it possible to use turn by turn navigation with AGPS?
If so how about the accuracy of navigation?

[Sutripta]

Hi,
I thought this GPS - AGPS thing had been discussed before.

To work, traditional GPSrs require a valid signal from >3 satellites, and some additional information to make sense of what is being received. This additional information is called the Ephemeris Table, and is also downloaded from the satellite. This table download requires a higher signal strength than just location information, and has to be downloaded correctly. Any error, and the whole process has to be repeated. The Ephemeral data is normally valid for 4 hrs. GPSrs normally download it every 0.5 hr. It takes time to download this data. And in a moving situation, chances of errors are extremely high.

It is this which delays initial lock, time to first fix (TTFF) after a cold start. Also, initial calculations are quicker if the GPSr knows approximately its location in space and time.

AGPS assists the gps by providing these information. If this information is not available, the GPSr will work as a normal GPSr. Initial lock-on will be delayed. After lock is achieved, there should be no difference in performance between AGPSrs and unassisted GPSrs

There is another technology which is long term Ephemeris data. This also falls under the broad umbrella of AGPS.

This additional initial data has to be downloaded to the AGPSr by some data link. GPRS, or computer connected to internet and to the GPSr via data cable, bluetooth, or WLAN or....

Regards
Sutripta

[NetfreakBombay]

Originally Posted by sanjayc

As per my understanding goes, with AGPS, the mobile sends the information of nearest cell tower and current time to the server. On the server, data regarding satellite positions are continuously avlbl and updated. This position is transmitted back to the mobile which now gets the appx long/lat co-ordinates from the server instead of the in-built gps receiver..over some minutes, if the inbuilt-gps is able to get a fix, this coords gets updated.

APGS primarily speeds up GPS fix by:

Downloading current satellite positions (ephemeris data) over GPRS

Usual GPS chips would download it from any satellite it sees for the first time, that is slow.