GPSlim 236 - Accuracy is misteriously gone!

gus779 · Occasional Visitor Joined: Nov 30, 2005 Posts: 10

Hello!

I'm from Brazil and have a Dell Axim x51v with a Holux GPSlim 236. My navigation software is Destinator PN (as it is the only option available here) and I've been using them for over 6 months without a single problem.

On this Sunday, at 8am, I was driving in Sao Paulo and, as usually, it was working flawlessly. Then I arrived at the place I wanted to get, stopped the car and turned all the gear off. Later, at 2pm, I got back to the car, soft resetted the Axim (as it was kind of slow) and turned on the GPS.

For my surprise, the accuracy was awfully bad... According to the GPS, I was most of the time driving between streets and Destinator would pick the one I was closest to, which wasn't always right. Telling me that I'm around 50 meter (or 160 feet) from my original location is very bad... And almost at every turn, the problem kept getting worse. Route recalculation was constantly annoying me. To sum it up: Holux GPSlim's so far perfect accuracy was gone!

I was using the same car I've had for over 3 years and the windshield wipers were turned off all the time. My first thought for the problem was that the number of satellites was insufficient, but it was never below 9 during the whole time of the trip (around 30 minutes). Destinator GPS icon was always green. I even tried turning the GPS off and then on again, but the problem continued. Then, the next day, everything was back to normal...

Does anyone have a clue of what might have happened? Does satellites have momentaneously problems? If I had another GPS (a substitute), would it work the same way, positioning me at the wrong place? Or can it be a flaw of my GPS? Or of Destinator?

A friend of mine once told me (he has the same gadgets as I have) that he had this problem when he spent the weekend in another city (Porto Alegre). He could only get a perfect position during 40% of the time while driving, but as it was his first time there, he thought the GPS could be right and the map could be messed up. But in Sao Paulo, the map is perfect, I can only blame the GPS. Or can the Destinator map get all messed up?!

Any thought would be very appreciated! Sorry if I wrote too much!

Thanks! :D

AllyCat · Posted: Mon Jul 17, 2006 12:05 pm Post subject:

Hi,

The most likely cause of your temporary problem is that the satellite "reference" data stored within the GPS became slightly corrupted. New data (from the satellites) is carefully checked before it is stored in the GPS, but there's always a small possibilty that "bad" data will be used. The reference data normally has a "life" of from some hours to days before it is considered "unusable" and is re-loaded. This determines whether the GPS performs a "hot", "warm" or "cold" start (so just switching the GPS off and on won't necessarily help).

If at any time you suspect that the GPS has bad data you could force a warm or cold start using software such as "GPSViewer", but eventually it will correct itself automatically. Alternatively, removing the battery for a few minutes might clear the memory, but many GPSs have a separate "backup" battery or capacitor to keep the data (and time/date) valid for several days.

Your friend's problem sounds more like bad map data or poor GPS coverage. But there can be many reasons for "inaccurate" GPS positions which usually can only be resolved by making more observations.

Cheers, Alan.
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gus779 · Occasional Visitor Joined: Nov 30, 2005 Posts: 10

Hey Allan!

Many thanks for your reply!

That was probably what happpened, now the next time this happens I'll force a cold start to get things get back to normal! You know, I was already considering buying a second GPS unit to the replace the other for these "inaccuracy moments", because without GPS I absolutely can't drive at all at big cities!

Thanks again!

Regards,
Gustavo.

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