OpenStreetMap

iPhone vs Garmin HCx

Posted by gormur on 16 April 2009 in English (English)

Two traces made on same journey by car.
Some roads were primary roads with 40-70 km/h and some residential areas with no more than 30km/h.
Garmin HCx (Tracking in fastest auto-mode):
http://openstreetmap.org/user/gormur/traces/359738

iPhone (set to track in some fast auto-mode I don't know):
http://openstreetmap.org/user/Antwelm/traces/359664

If you compare the two, you will see that the iPhone always has the "outer" curve when the road curves, while the Garmin sometimes "cuts" sharp corners.
Seems like the iPhone is a bit "ahead" of itself, while the Garmin doesnt always "react" to curves that well.

Still I believe that the track from the Garmin is the most accurate as it gives more detail in lower speed residential areas.

Location: Tananger, Kolnes, Sola, Rogaland, Norway

Comment from Longbow4u on 16 April 2009 at 17:03

It might be that the accelerometer affects the tracking in the IPhone 3G. I have an older Win Mobile PDA and a sirf3 GPS mouse which I think are pretty reliable, and an IPhone. I will track with those sets in parallel and check for discrepancies. My so far only tracks with the Iphone were in the forest, and accuracy might have been affected negatively by foliage.

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Comment from comsomol on 16 April 2009 at 18:29

What application were you using to get iPhone tracks? I'm using MotionX - this has an option to use accelerometer or not, which does indicate that you might get divergent results with iPhone. In general I believe I'd probably trust my Garmin more.

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Comment from Remiguel on 22 April 2009 at 19:05

Hi I have also made some tests with my Garmin 205 and my iPhone. You are right Gormur the iPhone seems to be more accurate than the Garmin tracking in curve and direction changing. It seems the Motion-X on iPhone allows to save much more points per second and works a lot with interpolation thanks to the accelerometer. In other hand the Garmin 205 has a Gps cell with a better refresh rate than the iPhone.
According my little experience, my Garmin is much more accurate on my position (less than 10 m) where my iPhone accuracy is worst than 15 m, but draws better traces and mostly follow better natural curves or direction changing.
I combine by now both results ...

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Comment from Antwelm on 3 May 2009 at 18:32

The iPhone trace mention here was recorded using MotionX-GPS. On the trace in question, the Accelerometer filter and Accuracy filter was turned on.

After a dialog with the MotionX/Fullpower staff, I now turn off the accelerometrix filter during all activities, as the only real thing it does is help with speed-calcultation while at very low speeds. The Accuracy filter is also turned off all the time, except while flying, since it's only real use is to better 'keep up' with speed-calculation and accuracy while at speeds exceeding 200km/t.

Recap: Both "A" filters off for any (by bike or car) OSM'ing..

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