iPhone accuracy

We ran some field tests in darwin with Bill Wade at CDU and noted there were discrepant readings across our various GPS sensors; iPhone 3GS, Garmin 60CS, Garmin 60CSX, and a bolt-on GPS toggle for a mid-range digital SLR camera.

I discussed this last week with an ongoing supporter of our project, Andy Roberts from NT Land Information Services, and was able to get very accurate survey point readings on our street to 'calibrate' the accuracy of our GPS sensing units. Armed with blueprints of points, accurate down to the centimetre level, my son and I went out and crunched the numbers across the Garmin 60CSx and the iPhone 3GS.
Cutting to the chase; we were able to get below 3 metres with the Garmin. The iPhone averaged out around 20 meters, got as accurate as 10 and twice was about 50 meters out [12 readings].  With the Garmin there is an Average function that allows one to leave the unit reading, over time, to sharpen its focus and we achieved around <3 metres after a 3 min sit. I don't think the iPhone has this higher end 'average' function ability to 'read over time'.  All things considered the iPhone does a pretty good job, the GPS transceiver is tiny from the pics I've web sourced, this is its 1st iteration [and will either get better next version and/or someone will offer an accurate GPS bolt on].  Now if they offered this bolt-on as Wi-Fi connected it would be ideal, fingers crossed.
The other thing to be aware of is the manufacturers guarantee which goes something like this for Garmin; for 95% of the time it will get you within 10 metres radius, for 4.5% of the time you'll get within 30 metres and for 0.5% of the time you may be as much as 300 metres out.  Nice waiver eh?
Another option we intend to interrogate is reverse geocoding the route entirely; that is lay the route out along the roads and tracks depicted on the map photographs, without having to log the route with a GPS navigator first.
As is mentioned in earlier posts, 60 to 78% of Australia, depending who you talk to, is without 3G signals.  Here in the Alice, surrounded by a desert the size of Europe... we loose our 3G connectivity 10 to 15Km out.  Hence our work and research on a system that will overlay Augmented Reality information to the outback/remote tourist or professional.

As well as the tests we ran in The Alice here's a London based scenario that backs up the conclusions we have come to.  Remember also that the iPhone is gaining extra location fix position information from cell phone towers.

I've just started testing the fidelity of the iPhone GPS in outback locations [no 3G signal ergo no cell phone tower triangulation assists.] Early results are confusing!!

You tube

Purple line is route taken White line is iPhone GPS track Cycle computer indicated total distance travelled as 3.56 miles, iPhone track indicated 3.4 miles