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Colorado's Position Jumping About!


Didjerrydo
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Is this kind of wandering about of position normal in the Colorado?: 1524jo2.jpg

 

This track log "occured" in a matter of 30 minutes or so while the unit was stationary at a fixed location. Seems like I never seen this much wandering occur with my 60CSx.

 

How drunk WERE you? :)

 

Kidding. Clear satellite view, I suppose? I haven't seen that (so far.)

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Is this kind of wandering about of position normal in the Colorado?: 1524jo2.jpg

 

This track log "occured" in a matter of 30 minutes or so while the unit was stationary at a fixed location. Seems like I never seen this much wandering occur with my 60CSx.

 

How drunk WERE you? :)

 

Kidding. Clear satellite view, I suppose? I haven't seen that (so far.)

Hey, just a few beers!..Yeah, actually the unit was laying on my coffee table indoors (but showing a a 14' accuracy. I will retry it outdoors but I really believe I'll see the same behavior.

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If you had a good view of the sky and a nice distributed satellite constellation (so the HDOP was low), I'd say the Colorado wasn't doing a very good job.

 

If the sky view wasn't very good and there were good reflecting surfaces to create multipath then what you are seeing isn't unusual.

 

I could take your 60CSx and put it in a location where it would record a range on the order of 50 ft. with one type of satellite constellation and 250 ft. with another. It could even record spikes out to 400 ft. or more.

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I will retry it outdoors but I really believe I'll see the same behavior.

It's been my experience that this is the expected behavior indoors. I don't think it's the expected behavior outdoors. I kinda wish that they could use some kind of analysis so that it wouldn't make track points out of those.

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You have a GPSr with a high sensitivity chip, trying it's darnedest to maintain a "lock" INSIDE, without a clear view of the satellites,WITH all kinds of reflected signals.........what do you expect??????

 

You'll get some of that "wandering" outside while stationary, but not to that degree.

 

Well, here's 30 minutes outside in a clear area: http://img152.imageshack.us/img152/282/outsidebm2.jpg

 

It's actually worse in some directions, plus I had to scale it out to 50' just to contain it.

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Mine is doing the same thing. I had it sitting on the desk, but with a good signal, running for an hour or so, and I was seeing errors of 100 feet or more. I will also set the unit on a tripod and see what it does. I did notice when I picked the unit up to look at the tracks the wandering got worse. Might try turning the compass to see if that affects it.

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Was this from a cold start, or after it had been on for 20 minutes?

Cold start

That's somewhat expected behavior. I wouldn't expect to see that kind of wandering, after the unit had been on for 20 minutes, and had a clear view of the sky. By clear view, I mean no obstructions at all, and no reflective surfaces (like tall buildings, cliffs, etc.)

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When my Map60Cx was new, I ran tests on it, laying down versus standing up using my bean bag mount, and when it was laying down, it had tracks going out a mile or so at times, but when I had it standing up vertical next to my PC, the position was stable with little wandering. so many people have compained about the 60Cx/CSx GPS units wandering, and figured that those people were not holding them as close to verical as possible. When A high sensitivity GPS is laying down inside or on a metal bench, they will be amplifying reflected and other bad signals. It is best to mount or hold the GPS vertical, to insure it will get higher quality signals.

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Well put , Got GPS

......however, when Poster after Poster chimes in with "GPS laying inside", "Cold Start", "Sitting on my desk",etc., while complaining about perceived problems, I don't know that there is much hope.

 

I wonder if a person could hear and see perfectly if they wore noise canceling headphones and had a tub over their head?

 

There are numerous posts in this forum and elsewhere (Manual) covering the correct procedures for assuring the best satellite reception and GPS operating instructions.

 

Your way is the absolute best, Experiment for yourself, and Learn.

Edited by Grasscatcher
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I seem to remember reading somewhere that these high sensitivity receivers use a thousand or more correlators in their architecture to look at the weak gps signals. The "wandering around" has something to do with this. My 76CSx does the same thing. The way to deal with it is to average the readings - something that the Colorado doesn't do yet. And even then, with a 1 second update rate, you can't average when you are moving. When placing a cache you should always average the coordinates for a couple of minutes to centroid on this "wandering around" behavior.

 

Hopefully waypoint averaging is in the next firmware update.

 

What is frustrating is when you're quite close to the cache and one second the unit says you are 8 ft. away in one direction and the next second you are 14 ft. away in the opposite direction...

 

I have seen one etrex receiver that had a systematic error of nearly 200 ft. The owner had placed some caches with it and nobody could find them unless their mojo was really working well. He ended up losing it before he could send it in for repairs (probably down under the car seat). Every fix was off by the same amount in the same direction.

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I seem to remember reading somewhere that these high sensitivity receivers use a thousand or more correlators in their architecture to look at the weak gps signals.

I've never seen any hard facts, but it's "known" that the old style receivers, like what you have in a GPSmap 60CS, uses around 20000 correlators, while the SiRFstar III and similar use about 200000 correlators. That's what makes them able to track in much worse situations.

 

As a general rule, older units didn't wander that much, because at these conditions, where modern GPS units do seem to ramble around, the old ones simply said "Lost satellite reception".

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I have a 400t (just got a replacement unit from REI since my previous 400t failed to keep time) and I went out hiking today for the first time with a 400t and a DeLorme PN-20. The terrain is mountainous with a lot of pine / fir trees.

 

Both units tracked about the same number of satellites (though at times the 400t was superior) and both gave similar EPE (varied from 16 feet to 30 feet or so depending upon conditions; the PN-20 lost reception a few times compared to 0 times for the 400t). I had WAAS enabled on both GPS units.

 

I noticed that, at times, the 400t seemed to get confused on the direction I was hiking: for example, I was going North, but it thought I was going East. The PN-20 was dead on track and didn't wander around like the 400t. I eventually disabled WAAS on the 400t which seemed to help for a while. But later, it happened again twice, and both times I did a compass calibration and it calmed the 400t down (which doesn't make sense since the compass can be disabled as of the 2.3 firmware, so isn't critical for navigation).

 

I'm confused...

Edited by jmedlock
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