[kman42]

Is there a way to turn off all the radios, except the GPS? I want to turn off the cell radio so the battery lasts longer, but Airplane mode also turns off the GPS. Would removing the SIM card work? Any other ideas?

[asxless]

I'd be interested in some way to improve battery life when hiking too.

I used our 3Gs during a bird survey the other day. I ran Motion X GPS to keep the track and record 8 way points during a 4 hour hike. Even though I started with a freshly charged battery, the 20% warning came on just as we got back. FWIW Wi-fi was turned off, i was not using the iPod function and the whole hike was in an area of 4-5 bars AT&T 3G service.

I now consider the iPhone's GPS as a backup to our Garmin eTrex. The iPhone only has enough battery capacity for very occasional use to see the aerial photos of the locale during any serious hiking.

asxless in iLand

[-Q-]

I don't think you can selectively disable the radios unless you jailbreak the phone. I saw an app to do that, but I can't track it down at the moment. When I find it, I'll post a link.

[kman42]

I've been searching for some solution without jailbreaking and removing the SIM seems the only plausible one, but I'm not sure if the phone searches for a network without a SIM card (I'd guess not).

We might just lug my wife's 3G iPad on the hike for the longer battery life (that is, if it ever shows up in the store). Can you disable the 3G on an iPad? Even if you can't, the battery will last longer.

We're going on a day hike to the Mendenhall Glacier so we aren't concerned about the added weight, but the trail is a bit off the beaten path, so it would be nice to have some nav with us. I'm pretty good with a compass and a map, but I'd hate to miss the boat!

[asxless]

Originally Posted by kman42 

....
We're going on a day hike to the Mendenhall Glacier so we aren't concerned about the added weight, but the trail is a bit off the beaten path, so it would be nice to have some nav with us. I'm pretty good with a compass and a map, but I'd hate to miss the boat!

FWIW what I do is....
Trace a Path in Google Earth -> Export it as a .kml -> Read it into MacGPS Pro -> Upload it to our Garmin eTrex.

This give us a track on the eTrex that we can monitor as we go. And the eTrex has both great battery life AND replaceable batteries But this is a fairly complex procedure, that requires a dedicated GPS device (e.g. eTrex), a Mac running Google Earth & MacGPS Pro and a little pre-planning

The poor battery life of the iPhone 3Gs when used as a GPS, reduces it to a handy accessory to our dedicated eTrex, on anything more than brief hikes (e.g. 2-4 hours).

asxless in iLand

[boy8cookie]

How would the phone pull the data necessary without being connected to the cell network? Unless there's an app you're using with cached versions of the maps, the map data has to be pulled over the cell network. Besides that, the iPhone (& iPad) use AGPS, which, I think, requires the cell network.

[kman42]

GPS Kit caches the maps and I think that while AGPS requires a cell network, you can still get unassisted GPS without it. It just takes longer to acquire the satellites.

[ghporter]

The 3G has less capable GPS (all AGPS I think) while the 3Gs has full GPS. No need for any network when you are depending only on the satellites. But kman42 is right, it does take longer to acquire the satellites.

Me, I keep my eTrex for hiking.

[Dork.]

Originally Posted by kman42 

I think that while AGPS requires a cell network, you can still get unassisted GPS without it. It just takes longer to acquire the satellites.

What he said. Assisted GPS is actually "better" than unassisted GPS. Assisted GPS gets satellite orbit (ephemeris) data and coarse position data through the cell network in order to speed up acquisition time. (The information can come from any other data channel, but cell phones already have another data channel, so the cell network is used.)

The ephemeris data is actually transmitted by the satellites themselves at an extremely low rate, and by obtaining the data through another channel the GPS receiver gets that data much faster. And with coarse position data, the receiver has a better idea which satellites to look for first. This can reduce the time to first fix to just a few seconds. Assisted GPS is pretty much required for GPS use in cell phones -- unassisted GPS would take too long. But even if out of range of cell towers, AGPS receivers ought to be able to get a fix like a non-assisted receiver would (if given enough time).

[Simon]

Both the 3G and 3GS have AGPS.

AGPS is full GPS (what would non-full GPS be???), but it ads some 'assistance' in that it gets rough positional information from the cellular network which speeds up getting a fix from satellite data.

AGPS is not inferior to GPS. It's just GPS plus an extra.

If an iPhone's GPS performance is worse than that of a dedicated GPS it most likely has to do with antennas and software. The A in AGPS has nothing to do with it.

[Dork.]

If the phone can't see enough satellites to get a fix (which is more likely than you think, especially in urban areas), the only position information it will have is the coarse positioning from cell tower triangulation, which is accurate enough to get you in the right part of town, but that's about it. When phone users see how crappy their position fix is, they may blame it on the "AGPS" feature on their phones, and not on the lack of signal in general.

[ghporter]

Originally Posted by Simon 

Both the 3G and 3GS have AGPS.

AGPS is full GPS (what would non-full GPS be???), but it ads some 'assistance' in that it gets rough positional information from the cellular network which speeds up getting a fix from satellite data.

AGPS is not inferior to GPS. It's just GPS plus an extra.

If an iPhone's GPS performance is worse than that of a dedicated GPS it most likely has to do with antennas and software. The A in AGPS has nothing to do with it.

My mistake. Maybe I was thinking of something about the original iPhone...? Anyway, some smart phones use a hybrid of the terrestrial "assist" from AGPS to produce somewhat more accurate location data than simple network translation will. This is fine in urban areas, but for hiking, you have either limited (and single tower) phone network access or none at all, which makes this hybrid system useless. There are also single-receiver "GPS assisted" location systems in some phones, which augment network triangulation with a high latency GPS location-which is not terribly accurate because the single receiver has to reacquire a satellite every few seconds. (No, I can't remember the brands. These lame excuses for positioning systems don't interest me enough to keep those names on my mind.)

I'd like to see portable Differential GPS systems in consumer packages. DGPS provides much higher accuracy by providing a terrestrial broadcast of known satellite inaccuracies, which allows the receiver to compensate and provide a much finer grained result. But that ain't gonna show up in a phone for a long, long time, if ever.

[anthology123]

I have used my iPhone 3G at Point Reyes National Seashore, which has almost no 3G (or barely even Edge). When I used Motion-X there, I can get a good positioning signal. I have to think that AGPS has little effect in this location, the phone signal was usually listed as No Service. It is a wide open area with little outside interference. OTOH, I tried to do GPS locating in Airplane mode with location services on, and I never got a GPS fix in Motion-X in Europe (UK and Italy). My Garmin 250 did get a GPS fix in both countries, though.

[BoulderDash]

Hey there,
So... there's no way that anyone has found (without jailbreaking) to make use of an iPhone 3GS' GPS while in Airplane Mode with WiFi enabled, correct?

I'm traveling to Cape Town and would like to use Gowalla to check in to some Spots while there. I called AT&T about its "Data Global Add-On" and the news isn't good for the country of South Africa. South Africa is not included in the list of countries with discounted rates. So, the only plan that they have is:

Data Global Add-On Non-Discounted Country
$59.99/month with ZERO megabytes included

No megabytes included... the price just gives you access to a network. Lame. I love Gowalla, but I won't be paying that much to play. ;-)

Does anyone have any ideas on how to get an iPhone app to use GPS while on a WiFi network with Airplane Mode enabled? Thanks so much,
BD