GPS vs Assisted GPS

10-15 meters in GPS isn't bad. The normal variances for GPS data for E911 is 11 meters.

Yes, google will still be able to triangulate your position (accurately too) without any form of cellular signal. it will pin point you perfect, but will just take a little longer as it's not using cell towers to triangulate too. however without a cell signal you cant download maps, so while the iphone will know exactly where you are... you wont! LOL!

the iPhone still remains a TERRIBLE GPS device to use when travelling at speed though as this review shows:
http://www.iphoneuserguide.com/apple/2008/07/28/iphone3g/report-gps-whilst-drivi ng/

I am on an oil rig in the middle of the GOM with no cell service and the GPS is not finding me. If anyone wants me to try some stuff while I am out here, post it and I will try it.

Without data (which is provided by the cell network) you may need line of sight from the phone to the sky and need to leave the phone still for 5 minutes while it gets its initial lock.

After it has a lock you should get a lock again fairly quick if you regularly use the GPS. If you don't use GPS for a week or two then it will be slower to get a lock.

@gilesjuk,
Minor correction: according to the GPS network specs, it takes 12+ minutes to download the complete data tables, and that assumes a reliable data channel from the satellite. Five minutes may not be enough to download the entire set of almanac data.

For precise GPS calculation, GPS technology needs clear line of sight to 3 satellites, which may be any place in the sky. (not quite any place; they tend to be more in equatorial skies). Hence, sitting at a window or beside a building with a clear view of the sky in one direction may not be enough to acquire lock.

@Danny,
You could download the TrackThing app from the App Store (free) and install it on your iPhone. Turn on Location Services, then start 'er up. TrackThing should be able to lock on to the GPS satellites and locate you. Once it acquires lock, it will display your co-ordinates (latitude, longitude, altitude), as well as speed, heading, and distance travelled. Unless your rig is moving, about the only non-zero readings will be lat and long. Maybe you'll see altitude changing with the tides. But at least you'll know the GPS receiver in your iPhone is working 🙂

You'll know you have GPS lock when the "GPS" label in the lower-right corner of the "Vitals" screen turns green. If it's red, you're not getting any GPS signals, and if it's orange, you have weak reception. I would imagine that in the middle of GOM, you'll get a solid green signal pretty quickly.

Do you have WiFi on the rig? If you do, and the iPhone is connected to it, and TrackThing doesn't find you, try turning WiFi off so the only means of location finding is from the satellites.

If you do have WiFi, once TrackThing has determined your location using GPS, it should display your location on its little map (the map info coming from Google Maps over the WiFi connection).

Stay safe - I can't imagine being on a rig in hurricane season.

Dave

Minor correction: according to the GPS network specs, it takes 12+ minutes to download the complete data tables,

That's only true if you can see only one satellite.

If you leave gps switched on all the time, it will build and maintain it's own 4 day almanac. This will generally be sufficient to yield 1 second lock times, if you keep the phone on with GPS turned on and take it outside.

I really appreciate the good information posted in response to my query, and thank all who provided it. It answers my question about the way the iPhone GPS works. But it also leaves me pretty cold, with respect to the device's capability in the wilderness. Since you cannot load Google Maps, you cannot "see" where you are, even if GPS does "know" where you are. Not exactly useful. I guess one can hope that, someday, someone will produce an app that will at least allow one to carry a database of maps on the iPhone that will work in conjunction with the GPS function, even when out of cellphone/wireless range. Until then, however, I think it would be fair to mention how the GPS relies on connectivity as well as satellite coverage, and not just the latter. That point is important to anyone who might think, as I used to think, that you could take the iPhone into the woods and use the GPS function to help find your way. (Most people should always bring a hard map and compass--and know how to use them--anyway, but you know most people. . . .)

With the way the IP "eats" the battery in GPS mode, IMHO the GPS is a nice toy, but not worth beans for any meaningful GPS navigational leg. On my unit, even with it plugged into my cigarette lighter port, it drains the battery faster than it can recharge although I suppose you can go a little farther with it plugged in to a DC port.

@d.r.c.

I have d/l trackthing and will try it offshore when i get out there monday. will let you know if it does work. i do have wi-fi inside the rig however, i could not get the gps signal due to all the metal.

A relevant article has been posted on Ars Technica that sheds a little more light on this topic.
http://arstechnica.com/journals/apple.ars/2008/10/20/using-the-iphones-gps-witho ut-a-network-connection

One thing I noticed in London is that if the iphone has an active Wifi connection, the GPS wa working OK, but the mas would not load in. As soon as I turned off wifi, and went back to 3g the maps loaded immediately

On another note theough, the maps located the theatre I was looking for and guided me faultlessly!

@GaryRam,
While in London, was your WiFi connection working for anything else? Could you receive mail, surf the web with Safari, watch YouTube videos, etc.?

It's possible that you were indeed connected to a WiFi access point ("associated with", to use technical jargon), but that the particular WiFi AP did not permit you to access the internet. I've noticed this several times while out and about - the little "wifi" symbol appears in the upper-left corner of my 3G, but I don't obtain any internet connectivity. This is one of the interesting quirks about WiFi. An AP can let you associate with it, but it won't assign you an IP address needed to connect to the internet.

You may well be right. I checked the id of the AP, which was BTopenzone which I thought was included in the O2 Iphone package. Interesting though that the iphone will not drop back to 3g wen the AP has a restricted access

@d.r.c.

I tried both trackthing and g-spot and i was able to get the gps to give me coordinates in the middle if the GOM. I took snapshots of the lat/*** and when i got into wi-fi, i punched them into maps and there i was.

so you can use the gps without and other means