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Nasty GPSMap 60csx accuracy issue - low battery, or . . .?


JohnInDC
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This morning (April 26), I fired up my GPSMap 60csx to use as an odometer on a bike ride. I thought I'd also take the opportunity to mark my house as a waypoint, a data point I lost a while ago during a firmware downgrade.

 

The unit had a view of 6-7 satellites, all showing the little "D", and was confidently reporting accuracy of 22-24 feet. So imagine my surprise when, in the map view, it showed me being a full quarter mile to the east of my house! This error persisted without resolution for several minutes (I thought maybe it was just transient) and so I powered the unit off and went for my ride. At my destination I powered it up again, only to encounter the identical problem - everything seems fine except for the quarter mile map error.

 

I have never had a problem like this at either location, and, until this morning the unit seemed to be working fine.

 

I can think of three possibilities, and solicit views on those or others. One is that there's something going on that's affecting GPS accuracy generally right now - solar storms, weather (it's overcast here in Washington DC today). I tend to think this isn't it, because the unit would, should, in that case self-report greater uncertainty than 24 feet. (More like 1200!) Two is, low batteries. (I have NiMH batteries in it, showing a quarter bar of power; the unit is set for these batteries.) I will be able to test this after putting in a fresh set later. Here too I can't help but think that the unit would report the inaccuracy. The third is, "defective unit". This is a rebuilt replacement model that Garmin gave me after my original one went belly-up a few weeks ago.

 

My prior unit was really great, and this one was fine too until today.

 

Any thoughts, anyone?

Edited by JohnInDC
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If you had left it on during your bike ride, and saved the location of your starting point when you got back, it would have shown correctly.

 

GPSrs are kinda like people.....they don't always think clearly when they first "wake up". You woke your unit up and asked it a question, then put it back to sleep when you didn't like it's answer. Then you left it sleeping for a while longer and then woke it up again and asked it the question again......and got a similar "sleepy" answer.

 

When GPSrs have been off for "a while", and then turned on, they may show to be "locked on" to satellites but not have a good "almanac" of satellite locations so their calculations may not be as accurate for the first few minutes.

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I understand that it can take a few minutes for the device to settle in but 1) that's why I stood still for several minutes, waiting for the thing to sort itself out; 2) I've never seen this kind of warm-up error before, in a year's worth of use; and 3) why would the unit report accuracy of 22-24 feet when it was more like 1250? Finally (4) - someone else reported the identical problem just minutes after I posted this topic.

 

http://forums.Groundspeak.com/GC/index.php?showtopic=161878

 

I'll put in fresh batteries tonight, and see if that makes an immediate difference. I will also let the unit sit for half an hour or so and see if it works its way back to the right spot.

Edited by JohnInDC
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You might also download Trimble Planning software (free) and use it to determine what the conditions were in your location at that specific time.

Be sure to get the latest almanac.

 

There may have been a spike in the PDOP values at the time when you were starting.

 

With the software, you can actually tell which specific satellites your unit will see before you go outside . You'll also start to understand why there are times when it is impossible to get good position readings with ANY GPSr....including $6000+ survey quality units.

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Well, whatever the problem was, 12 hours later it seems to be resolved. The unit is back on track, and has me once again pegged, on the map, to within a few feet of my location.

 

It almost sounds like you were experiencing a similar problem I had a few months ago in Mobile, AL. For no apparent reason when traveling down I-65 South to Mobile my GPSr instantly started showing a greatly degraded signal - went from receiving 11 satellites to receiving only 6 or 7. The location I held the unit in my vehicle made a hugh difference now when prior to this it has never made a difference on satellite reception. This strange phenomena continued for the entire week I was in the Mobile, AL area and at times I would loose all satellite signal for just a brief moment, but for the majority of that entire week I was getting a greatly degraded satellite signal. Now my trust in my GPSr is waivering.

 

So, I called Garmin questioning them as to what may have been happening. They had no real explanation and said that they were not aware of any degraded signals in that area. "Degraded Siganls ???" Garmin did explain that there are places in the country that the satellite signals are greatly degraded for security reasons - White House, Pentagon, some military bases, etc.

 

Since these degraded satellite siganls can be turned on and off as was my experience in Mobile, it is possible you may have been experiencing the same thing in Washington D.C. After many return trips to Mobile, AL I have not experienced this degraded signal any other times.

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I suppose it could have been just about anything. Again the weirdest part to me was that the unit was so - *confident* that I was several blocks away. "Yes, yes, I'm 95% sure you're within 22 feet of this spot!" If it were a matter of general signal degradation or interference, I'd expect the unit to detect the anomalies in the satellite signals and report a much higher margin of error.

 

Hm. Maybe the unit just uses some cheap shortcut algorithm to estimate accuracy, and that while it's more-or-less right most of the time, when you come down it the number is just kind of an invention, and not really accurate in usual circumstances.

 

It reminds me of Mac OS X, 10.4. When you boot a Macintosh, there's a blue progress bar that tells you how far along in the process you are. Prior to 10.4, the bar corresponded to different points in the process; and while the bar advanced a bit jerkily, it gave a generally accurate view of where you were. In 10.4 they abandoned the "real" reporting with the bar -- now the computer just averages the time it took to boot on a few preceding occasions, and draws a blue bar that smoooooothly fills the box in that calculated length of time. It's more or less right, most of the time, but not when something new is introduced into the boot process.

 

Big digression, huh. Anyhow, that's the kind of thing I mean. Maybe something happened that completely foiled the unit's ability to talk about it with the 'accuracy' algorithm it uses.

Edited by JohnInDC
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Try the Trimble Planning software mentioned above .......you will start to understand what is going on and can even do some "experiments" with your unit. Pick a time when the software shows that the conditions are lousy at your location , and go out and try it.

 

It will erase a lot of misunderstanding and ???????

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I posted this on the related thread also :

 

Yesterday I took my dog for a hike. I hadn't used my Map60csx for awhile, and so I thought I would take it along. I noticed right away the accuracy was way off. I usually get 9-12 ft., and it was showing 50 - 80, and varying all the time. After my walk, I looked at the "trip', and it said almost 3 miles. This, on a route I know to be 1 1/4 mile. It was cloudy, so I thought, bad signal because of weather, although I never had that happen before.

So today I get the unit out and fire it up. Beautiful blue sky's. My accuracy is showing from 24 ft. to as high as 100 ft +. varying again, all the time. I am at a loss, and looked on this site for any others problems. Seems it is something many others are experiancing. I thought at first maybe it was the recent software upgrade, as I hadn't used my unit since I upgraded. It appears this is not the problem though.

Just posted so others are aware many are having problems.

Thanks to anyone that can give us help with this issue.

 

Dave

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I had a similar problem the other day. (I don't remember if it was the same day or not) I went looking for a new cache, so turned on my 60csx. Gps was leading me into the middle of the harbour. Went back to the car and noticed my gps had me standing in the lake when I was clearly parked on dry land. Checked the waypoint on the Quest in my car (which was showing me on land. Both units were using CN8 maps) The quest and 60csx were reading about 250-300' off. I could have taken the quest and went and lookid for the cache, but I descided to come back another day.

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