... in the wilds of Knoydart.

So you take your phone/mobile device, probe for the nearest wi-fi networks, and based on the signal strength, you can estimate your position from the "known" position of the wi-fi assuming that the position of the wi-fi units are accurate.

You would still suffer the same issues of GPS when you're indoors, depending on the building.

Having a Nokia E90, I can tell you that in an urban environment, your accuracy is within 100 feet. (I just tested my phone with a beta of Maps 2.0.) The issue is really bad when you can't get a good fix on the sat signals.

Of course I'm told that the chips in the phones are not the same as in the car based nav systems or Garmin like devices. (Much greater accuracy, down to 1.5 meters or so.)

But if you want to improve the accuracy of the sat systems, just add a base station at a known location. Like something atop of the Sears Tower. Then you can improve your accuracy greatly. Phone companies which already have Cell towers could add base stations at strategic locations so your accuracy improves without the costs of maintaining a database of wi-fi spots (mostly private), and extending the life of the cell phone battery.

While its a nice technology, I don't think its one for the phones.

A better use would be to track individuals within a building or a warehouse. There you can use a small wi-fi device to pin point workers within a complex...

;-)

My mate's got an iPod touch with Google Maps, and that seems to already do this. He's tried it in several locations, and the accuracy varies, but generally it'll pick out which building you're in.

Does anyone know how it works?

The technology you're referring to is already in extensive use by farmers, so they can automate their tractors going around their fields, using GPS with a base station located on site broadcasting the GPS correction info; this makes it accurate to about 2.5 inches.

I agree that for the network operators to install it on their masts would be best, but that would involve investment by the operators in something that can't be marketed, or limited to their customers... the marketing bods wouldn't be able to convey that GPS is a one-way system! (and in a phone, it needn't be either)

The iPhone and iPod Touch do indeed do wifi based locating, not to a level of 5 metres granted, but it's pretty good. They use technology from these people: www.skyhookwireless.com/

I believe Google maintains a database of mobile cells along with their geographical locations. The maps application can use this to divine your current location if your device supports it - quite a few phones do.

I assumed that google maps works the same way as the system in the article. Then I thought that it might work by knowing the physical location of the IP address of the base stations. Some database somewhere that tracks them all.

Initially when I got my Touch the locate feature didn't work and I kept trying it out wherever I went. One evening I was at a friends house in the wilds of Harrow and logged into his BT home hub (to show him how much better the web browser was on the Touch than the browser on his N95!) We then went onto the maps - he's got GPS, I haven't. But to my surprise, the map came straight in and within about 3 seconds, a circle of about 50m radius was drawn and I would say that his house was probably about 20m from the centre of the circle. When I got home I tried it again and the new map came up and the circle was less than 30m and my house was bang in the centre. Now I have 2 base stations, an Apple mushroom and a BeBox. The Touch connects automatically to the Mushroom.

A couple of days later I was at a client's house in Hammersmith. I tried it there and the map came up but the circle was probably 80-100m radius and the house was off-centre by about 10-15m (it's hard to judge at that scale). After about half an hour I tried it again and this time the map zoomed right in and I had a circle of about 10m with his house dead in the centre.

In the last couple of days my mushroom has decided to misbehave and so I have turned it off. Now connected to the BeBox (rubbish thing that it is) the Touch still gives me the same accuracy on my house.

You already can do it with Wifi - I'm currently trialing a wireless solution from a supplier that lets you plot your buildings, plot where the access points are, then it can trianulate where your wifi device is.

They're starting to do it in hospitals with the medical equipment/trollies/wheelchairs e.t.c. This is simply an extension of this type of service. Should be OK, but in central london, google maps 'My Location' is good enough on a WinMob as all you need to do is look at the map and compare that to the nearest street junctions and you know where you are, as attested at the weekend when GPS was ultimatly too slow.

Yes, I know.

Use of a base station set up for 48-72 hours prior to use can give you accuracy in cm. (You have to allow for some time so that the base station can auto correct.)

The point was that the tecos could add these base stations at a minimal cost and over time, the TCO would be less than trying to rely on wi-fi spots which will not give you the 5 meter accuracy because you don't know the "exact" position of the wi-fi antenna.

There's another system that could also be used. LORAN-C.

http://en.wikipedia.org/wiki/Loran-C

Now I'm not sure, but doesn't the radio signal also travel through the walls of buildings? So in theory you could triangulate against those signals, and depending on the clock in your portable device, time of day, etc .. your accuracy will vary.

The point is that in addition to GPS, you could also use LORAN-C

The Google my location service does not work on my handset, which would explain why I managed to get lost walking round Portsmouth and end up 4 miles from where I was supposed to be.

I hope this works, would be amazingly useful for me, I think in the mean time though I may have to purchase GPS...

Yes, that would be a better use of "wi-fi" because you can find your position relative to the wi-fi transmitter and you don't need to know your position relative to the outside world, which is what GPS is used for.

Like I said, its neat technology, however, with respect to GPS positioning, its not going to be accurate enough to be viable. It would be cheaper to implement GPS within the phone than to try and use Wi-Fi.

LORAN-C would be a better augmentation to GPS for purposes of navigation.

Navizon's database is now pretty big and world wide, they have been collecting for several years now. Its not just limited to area's around commercial AP's either and covers phone cells points as an additional check.

Works on all phone platforms and they pay you for mapping - its rather lucrative..

The area inside the m25 has over 500K mapping points in their database for instance and in busy areas like central London accuracy can be with a couple of meters.

why are companies trying to put wi-fi into everything regardless of whether it will a deliver 'real' benefit that can also be commercialised? All it does is waste money, effort and talent that could have been used for something that would last because it is useful.

http://www.theregister.co.uk/2007/03/20/aim_location_plug-in/

"corrected" GPS- GPS augmented with known-location base stations- is called DGPS, or Differential GPS.

It really is great, we use it at work for positioning ships, laying pipelines, and other such underwater construction stuff. Decimeter precision accuracy just about anywhere in the world IIRC.