BT-338 Speed out?

DwayneDibbley · Lifetime Member Joined: Jul 01, 2005 Posts: 2

I have a BT338 and ipaq 2755 running GPSinfo COM8: 38400 when testing in my car at 40 indicated on the car the GPS info report 22 MPH at 70 reports 50 seems to be 10-20 MPH out anyone else seen this?

Thanks

andyjenkins · Regular Visitor Joined: Apr 02, 2005 Posts: 74

Given the [usual] accurace of GPS units, are you 100% confident that your car's speedo, is not the one that is wrong ?
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iankb · Posted: Sat Jul 02, 2005 4:56 pm Post subject:

The speed is calculated by the software, based upon the change of GPS positioning. The BT-338 would only be at fault if it were reporting positions with varying inaccuracies. It might do this if you have poor satellite acquisition when, I believe, the Sirf III chipset will try and make senses of the last positions received. If you aren't using map data, that could prevent the positions being snapped to the nearest road, and so could report positions oscillating either side of the true position. However, that would increase the distance travelled and so increase the estimated speed. Given that GPSinfo seems to be underestimating the speed, there is either a bug in GPSinfo, or your speedo is way out.

Do you get the impression that everybody drives faster than you, and do people behind keep flashing you? Wink

Do you have navigation software, and do you know whether it is accurately reporting your position? I don't know what GPSinfo would make of incorrect positions if, for instance, you had the time set incorrectly on your PDA.
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Ian

iPaq 2210
Globalsat BT-338
Seidio G2500 Amplified Vent Mount
CoPilot 6, GPS Tuner 4.2, Navio 3.01
BMW 330ci Sport

DwayneDibbley · Lifetime Member Joined: Jul 01, 2005 Posts: 2

GPS looks OK, its GPSINFO that displays incorrect info. repeated the same run with MemoryMap and TomTom both report correct speed. So i guess GPSINFO is a bit naff and shouldn't be taken for granted.

Thanks Anyway

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