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Odd Gpsr Behavoir?


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Let me start by saying that I'm a ways from being new at this. I've owned my Magellan Meridian GPS receiver for nearly 4 years. That being said, I've noticed some "odd" (annoying?, peculiar?, unexpected?) things that it does that I've come to accept as "normal". I adjust for these "anomalies" when I'm out finding and placing caches. These no longer bother me but it's just one of those things that've been rolling around in the back of my mind and I *finally* decided to post about it and see what others experience.

 

I'd be very interested to know what others have noticed with their GPS units. Odd or unexpected behavior? How do you compensate? I know (believe?) that the (vast?) majority of cachers own Garmin units. I bought a Magellan because when I discovered Geocaching one night while searching the web for something else, the stores were closed and I couldn't wait to get started. So... I ran to that "big box" store that stays open late and Magellan was what they were selling. I bought one and the rest, as they say...

 

Now, for my Magellan pecularities:

 

1. When I'm searching for a cache and walking at a normal pace with my GPSr held in front of me with the arrow pointing the way, the Magellan seems to be "leading" me as I walk. That is, as I near the cache and the distance closes, when the GPSr says I've arrived I've consistently gone 30-40 feet past where it really is. The Magellan seems to be "anticipating" where I'm going to be. Once I wander around in the vicinity (ok, well, it's actually a little more "structured" than wandering around since I know how the Magellan behaves) the arrow and distance to where the cache really is closes until I ultimately locate it. Once I've located the cache and the GPSr has settled in at the location, I find that my coordinates are very accurate when compare to the cache page. (Yes, I have WAAS enabled).

 

2. When I'm placing a cache it is my custom to visit the proposed cache location on several occasions, on different days, and at different times. I try to get at least three waypoint readings then take the average. If one is completely off I'll discard it and get another reading. What I discover is that the values that I get for latitude are very consistent from reading to reading. Longitude is another story altogether. The values I receive can vary wildly (as much as 150 yards between readings). Let me say that when taking a waypoint reading I let the GPSr settle for at least two minutes before taking the reading. So, what the heck is it with longitude?

 

Ok... There they are. My little oddities. Thoughts? Observations?

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I carry around more than one GPSr with me while Geocaching. Often, I have three, but only use two at a time.

 

On my Magellan GPS Companion, I HAVE noticed the "longitude problem" now that you mentioned it. I've always attributed it to power lines, fences (including and ESPECIALLY cyclone fences), walls, and forest cover, but one day, it was consistently off by 0.003 to 0.004 minutes on the longitude compared to a Lowrance iFinder GO in a public shore area without any obstructions (latitude always matched). I guessed that it had to do with WAAS (Lowrance has it, but the Magellan doesn't) but now you got me thinking.

 

My main GPSr is the Garmin eTrex Summit. As with other Garmins, it updates its position quickly, so anomalies don't linger, so they don't get noticed easily. I can make it "behave like a Magellan" by switching to battery save mode, which makes it update its position much slower. One time, I had the distance jump from 250' to 5' while walking along a hillside.

 

The Lowrance iFinder GO is a little too sensitive, so I'm guessing it calculates positions with bad signals. I've been off by more than 100' on many occasions, especially in thick forest cover. This also happens when I leave it on inside my car away from the windshield. This is easily fixed by power cycling the unit.

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Now, for my Magellan pecularities:

 

1. When I'm searching for a cache and walking at a normal pace with my GPSr held in front of me with the arrow pointing the way, the Magellan seems to be "leading" me as I walk. That is, as I near the cache and the distance closes, when the GPSr says I've arrived I've consistently gone 30-40 feet past where it really is. The Magellan seems to be "anticipating" where I'm going to be. Once I wander around in the vicinity (ok, well, it's actually a little more "structured" than wandering around since I know how the Magellan behaves) the arrow and distance to where the cache really is closes until I ultimately locate it. Once I've located the cache and the GPSr has settled in at the location, I find that my coordinates are very accurate when compare to the cache page. (Yes, I have WAAS enabled).

THis *is* a Magellan characteristic (the pre-Explorist models, anyway)...it does something like a moving average, factoring in recent readings with the current reading. In many situations this can be a plus, smoothing out some of the irregularities in readings that budd-rdc describes above. But for caching, it results in the so-called slingshot effect. People who are aware of this will typically stop for a minute or two as they get within 75 feet or so of the supposed destination to allow the unit to "catch up" with itself by letting the recent readings elapse from the moving average calculation. Another way to do it is to turn the unit off and turn it back on; that will quickly erase the memory used for moving calculation, but you probably will have to re-set the GOTO.

 

2. When I'm placing a cache it is my custom to visit the proposed cache location on several occasions, on different days, and at different times. I try to get at least three waypoint readings then take the average. If one is completely off I'll discard it and get another reading. What I discover is that the values that I get for latitude are very consistent from reading to reading. Longitude is another story altogether. The values I receive can vary wildly (as much as 150 yards between readings). Let me say that when taking a waypoint reading I let the GPSr settle for at least two minutes before taking the reading. So, what the heck is it with longitude?

I've not noticed the longitude aspect, although that may well be due to inattention on my part. Budd-rdc gave some good reasons why readings may be inconsistent in a general sense. Since your unit does position averaging automatically, you will probably see better consistency if you give it some more time. Two minutes is pretty short; I'd say five minutes at the least and for a read where accuracy is particularly importand (e.g., a cache) 10 or 15 minutes would be better.

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I have owned 5 magellans and two garmins, and I must say that most of the things you are talking about are only in magellan gpsr. besides these issues all of the magellans had there own little bugs. the most recent magellan I owned was a explorist 400.

 

All I had for comparison was our legendC, when marking waypoints walking along a semi open trail, the magellan would get totally different numbers than the garmin.(both on same coords system/datum) after finishing our walk we procedded to go back to the waypoints we created. even though the magellan & legendc took coords in the exact same spot, only the legendC went back to that spot. the magellan was putting us 80+ feet up the trail farther. so we plunked in the coords the legendC took, and then the explorist400 was able to find the spot. I should say both units had below 20ft claimed accuracy when taking coords.

after that comparison I learned I had to take TONS of reading to get anything close to accurate with the magellan, I dont think my meridian gold was ever this bad.

 

we went to a few caches with both units and they both seemed about the same. then we went to an area in a deep valley and heavy tree cover, thats when the magellan started acting like the old ones I had. standing on the cache, the legendC said we were 12ft away, the explorist 400 was reading 200+ ft away. so I walked to where the exporist 400 ground zero was at, up at the top of the valley out in the open..... I was hoping improving the signal would change things..... nope after standing there for 5minutes, the unit was 100% positive that spot 200ft from cache was where I should be at. I turned it off and tried the goto again..... same thing..... checked coords to see if they were input right..... yep they were the same. we went to the next cache and the unit was fine...... very strange. at least with my old magellans when they over shot the cache it at some point it would know it was wrong.

 

this was with the most recent firmware installed, and the unit was only 3days out of the box.... needless to say it got sent back & I wont buy another magellan again.

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Max Speed 1,084 M.P.H.!!!

 

I NEVER FLEW ON THE CONCORDE! :)

 

1585400_200.jpg

 

I was standing on a corner in Washington, DC doing a MetroGuide search for fast food when I noticed numbers behind the menu changing rapidly. Looked at the map and it showed me in N.E. Canada!! I let it go for a couple minutes and then turned it off and then back on again to see if it would fix itself. It did indeed function normally when I turned it back on. Then it dawned on me that I should've left it on to let it continue to circle the globe! That would've been an awesome saved track! :D

 

I started a thread on the old message board about this, but it seems to be lost. Others accused me of taking good drugs or just being generally insane (not far from the truth, but still not a factor in this case). One guy beat me - had over 4,000 M.P.H. on a yellow Etrex! So, evidently not a problem limited to just Legends. Some Maggie users also had similar stories too. One guy attributed the phenomenon to bad reception - which indeed was the case with my being on a street corner in DC.

Edited by Neo_Geo
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Max Speed 1,084 M.P.H.!!!

 

I NEVER FLEW ON THE CONCORDE! :)

 

I was standing on a corner in Washington, DC doing a MetroGuide search for fast food when I noticed numbers behind the menu changing rapidly. Looked at the map and it showed me in N.E. Canada!! I let it go for a couple minutes and then turned it off and then back on again to see if it would fix itself. It did indeed function normally when I turned it back on. Then it dawned on me that I should've left it on to let it continue to circle the globe! That would've been an awesome saved track! :D

 

I started a thread on the old message board about this, but it seems to be lost. Others accused me of taking good drugs or just being generally insane (not far from the truth, but still not a factor in this case). One guy beat me - had over 4,000 M.P.H. on a yellow Etrex! So, evidently not a problem limited to just Legends. Some Maggie users also had similar stories too. One guy attributed the phenomenon to bad reception - which indeed was the case with my being on a street corner in DC.

 

Something similar happened with a Garmin Geko 201, where it kept travelling NNW in a straight line and flew right to Washington State. The Geko 201 was inside the car away from the windshield, so I suspect bad signal was the culprit. I've heard 60c and 60cs owners having experienced this before, and if I recall, the Geko, Legend, and 60c were all released around the same time? (I smell firmware or chipset issue!) My older eTrex Summit hasn't done this yet.

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I'm currently having two things happen with my Meridian.

 

1. I put in the coordinates for a local cache (in NH) that should have been a mile away. Then I hit goto and selected that waypoint. The goto line went 67 miles right into the Atlantic Ocean. No matter what I did, I couldn't fix it.

 

2. Recently I've entered waypoints and then a few minutes or 10s of minutes later shut off the GPS. When I turn it back on, the waypoint is GONE. I have no idea what that's about.

 

In fact, I used the GPS for an entire round of golf and did a waypoint at the middle of every green on my local course. During the round I had to change batteries (this was around hole five).

 

Once the battery change was done, I lost the waypoint I put in the night before for my home AND I lost the second hole (I hadn't put the first in because we were holding the twosome up behind us.

 

Any thoughts???

 

Jeff

 

http://www.alifeofplay.com

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Neo Geo, I was in Iowa doing 41275 MPH when I was actually in a Quicktrip getting a cup of coffee (North of St Louis MO 14 miles west of where the Missouri river and Mississippi rive meet), the Garmin legand c was left in my truck outside. I noticed it when I was telling my wife how it kept track of your max speed. Garmin sent me a new GPS, did the same thing. On my 4th GPS a Legend cx and have had some of the same odd things happen with it.

Edited by saw-saw
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My GPSr has always been reliable, although I have watched that little triangle "fly" over the map screen after it lost the signal. <_< One time it recorded a speed of over 900 mph doing that. :)

 

However, yesterday it did something odd. I turned it on and it said I was in the middle of the Pacific Ocean. :rolleyes:

 

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It was quite insistent and even when I held it so it could acquire more satellites, it stayed like this. So I took a picture, then turned it off and back on.

 

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It found the correct satellites and recorded where I really was. Whewwww . . . I could stop treading water . . . finally. :rolleyes:

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My Gold did the speed and location thingy once shortly after I bought it in 02. I was in a narrow and steep sided canyon and realized I'd lost sats.

As far as I can remember that was the only time, and have had nothing screwy happen with my exp.500,and don't remember ever having anything happen with my old Lowrance GN 212

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