I am researching to find out how a iPhone/Anroid cell phone GPS works.

I've heard that some phones get GPS data from cell towers while other phones have a stand alone GPS receiver/system.

I'd appreciate some feedback and references.

Thank you,

Blake

www.outdoorquest.blogspot.com

All the "smart phones" have a GPS receiver. I suspect you are confused by E911 capability. This is the system to provide a location when you make a 911 call from a cell. Phones without GPS or with their GPS turned off will get an approximate location via cell site triangulation.

However, I have read that most smart phones don't maintain local copies of the maps, so you still need to be in cellphone range to use GPS mapping. I also wonder if you can get topo maps on a cellphone.

There are apps that allow maps to be uploaded, but I haven't tried them as yet. I still rely on "real" GPS units for my navigation - both on the road and off ... in addition to paper maps.

I have a friend (actually my son's Scoutmaster) who works for a recently purchases mobile phone company. I asked him about the details of GPS location on smart phones, and he pretty much said what Doug just said. They have GPS chip sets AND have the ability to triangulate via cell towers using signal strength to provide pretty good location without the GPS chip.

I lost my faith in the smart phone navigation when this Scoutmaster missed several turns on the way up to summer camp because his smart phone lost signal (or at least "hesitated" in its updating) just before the turns came up. My Garmin Nuvi simply does not do that.

My previous Nuvi had a tendency to reboot spontaneously and ultimately refused to start up one evening ... in downtown Detroit ... in the pouring rain ... with the battery in my smart phone almost dead. Sigh. Luckily my smart phone had enough power to get me back up onto the highway - where at least I knew where I was. I bought a new Nuvi on the way home the next morning.

Both iphone and Android have internal GPS. When they don't recieve a satellite signal (for example indoors) my understanding is that they triangulate from cell towers, which is less accurate.

There are aps available for the iphone with which one can download local copies of maps. I have not tried them, so I cannot speak to how well they work.

While I use my iphone extensively as a GPS in town, and sometimes carry it as a back when hiking, I don't consider it a substitute for a regular GPS for wilderness use. My experience is that using the GPS sucks the iphone batteries down rather fast. Also, iphones are somewhat fragile and don't like getting wet. Other smart phones may be less susceptable to these problems.

I really like my iphone for in town use, but out in the woods, I rely primarily on traditional navigation with a map and compass, using a stand alone GPS when necessary.

I really liked iTopoMaps on iThings for downloadable maps, but it stopped working with current iOS software and didn't seem to get any updates. Now I'm using MotionX-GPS for that purpose. Just make sure to download any maps you're going to need in advance, preferably over Wifi.

When I'm out and about, I'll drop a "pin" at my campsite, car, trailhead, or any other place that I might want to be able to find again. Then I put the gizmo away (in a water- and shock- resistant case) and navigate with map and compass. For me, it makes a good backup.

I currently use a Samsung GT-B2710 phone which has an inbuilt LED flashlight, Electronic Compass, FM Radio and GPS (which is sensitive enough to work indoors) using a JAVA app called 'UTM Data', which will convert the GPS WGS-84 coordinates generated from the internal GPS receiver to a host of other datums such as OSGB36, MGRS and UTM etc for paper map use i.e the UK Ordnance Survey 1:50,000 and 1:25,000 Topographic paper maps. The phone is unlocked, has excellent battery life, and easily charged using a Sunlinq 6W panel or external Lithium Battery pack etc.

www.youtube.com/watch?v=0vHfKq8CREk

Do not attempt this with your $600 iPhone.

For electronic mapping I also use a Ployer Momo 9 (Android) Tablet PC with the Maverick Pro App (no inbulit GPS or 3G, although a 3G USB dongle can be attached to the USB port). This allows me to cache most download maps that are available including OSGB (except it seems Google Maps). This gives me even more extensive electronic mapping capabilities for the UK than even the Satmap Active 10 Plus GPS (typically costs £300). SD cards for complete OSGB electronic map coverage of the UK may add another £300-400

The Ployer is cheap at around £100 and maps are cached on a 16GB micro SD card when working without any WiFi or 3G connection.

The main problem with electronic mapping and navigation is the compromise between display size and weight, battery life, fragility and the manufacturers insistence of using their own non standard mapping formats, for which you pay a hefty price, whilst the some companies (Google, Apple ahem) like to keep a track of where you are.

The main advantage is the amount of data that can be stored on a microSD is very impressive. i.e Coverage of just Scotland on highly detailed OSGB 1:25000 topographic paper maps would weigh many times the weight of the tablet computer itself.

If going lightweight for a weekend I would just take a paper map/compass and the Samsung Phone (mainly for communications if within network coverage and for the occassional GPS fix if visibility is very poor). The Ployer Momo 9 might come along if it was a bug out situation.

My phone can use GPS (5 meters accuracy), and if it's off it'll use cell tower triangulation (500~1000 meters or so accuracy, or if wifi is on and there are access points around it'll use WPS (almost as good as GPS in populated area with a lot of WIFI signals).

As far as map goes, if you use an ONLINE map service such as google map obviously it won't work when there is no signal (though you can pre cache area in gmap if you choose). You can download navigation apps or topo map apps that will store them locally, I have sygic navigation installed for back up. (though you do need a couple of GB of free space for the maps, 4.7 GB in my case)

Well I have never had luck with my iPhone off grid, out of cell range, using my GPS. I just don't rely on it out of cell range.

But for those of you who geocache in cell areas, the geocaching.com app is amazing on the iPhone. I haven't had to use my dedicated gps in years to look for caches.

Google Maps recently added an option to store selected maps on the phone. Actually they've had it for a while, but it was a "Lab" beta feature. Now it is part of the core product.

It's in version 6.9.0. Press Menu, then "Make available offline".