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Thread: GPS inaccuracy

  1. #1
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    GPS inaccuracy

    Hello -

    My carputer is mostly up and running - screen installed, MP3s playing, etc. I've been experimenting with GPS, and having a problem that I wanted to ask about. I'm using a Garmin eTrex Summit with a serial cable to my PC, and I find that the position it shows is consistently around 1500' off. It doesn't actually matter if I'm using iGuidance, or a GPS app on my Mac (for example) or even just pulling the coordinate data and looking it up with Google Maps; it's always wrong. I just tested this standing on my porch - the Mac sees the GPS is tracking 7 sats, and the GPS is reporting 25' accuracy, but it shows me being five blocks away. Nothing weird about my current location either - I had this problem while driving two/from work yesterday and today.

    I just upgraded the firmware of my GPS to the latest, but there was no change. I don't know what else to try - anyone have any ideas? It definitely seems confined to my GPS itself.

  2. #2
    lez
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    GPS is never wrong, its either user error or a duff unit.

    I know ppl are now going to go on about how gps can be wrong etc, but please dont waste time, if a unit is off more than 30ft all the time its a bad setting in the units options or a dufff unit.

    As an ex-etrex user I can say they are spot on accurate all the time with 3+ sats, I do not know the summit model but mine had lots of options in the menu's

  3. #3
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    I fixed the problem. I found a set of debug commands for the Garmin GPSes, and one for mine forced it to do a cold start. I performed this, and took it outside to let it reacquire satellites and build a new position almanac. This took about 10 minutes, after which it had a 30' accuracy as I've seen before. Back inside with it hooked up to the laptop, it finally showed my position with good accuracy, much more like what I expected.

    If anyone else has this issue or wants to experiment with the debug commands for their Garmin, the site is here:

    http://www.gpsinformation.org/dale/secret.htm

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