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GPS off or is it me?


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With an open view of the sky, sometimes you'll be within a few feet. However, many caches aren't placed in an open field, so we have to deal with less-than-ideal satellite reception.

 

As Stunod said, with any tree cover or other areas where the sky is partially obscured, 30' is about right.

 

After finding a few more, as you approach the coordinates on your GPSr, you'll start looking for places where you would hide a cache. Most times that place is where it's hidden.

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To have all three off by the same amount is a little odd, but 30 feet is within the normal range of error. Your GPS should give you an estimated position error when it's locked on; 15-20 feet is typical under open skies. The hider of the cache had to contend with a similar amount of potential error. As a result, few caches are found right where your GPS is pointing. I'd expect a little more variety in your distances, but see what happens after you find a few more caches.

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If you reallt want to check it out, go find a local Benchmark.

 

Geocaches are placed by humans with the same type of devices as you, therefore margin of error is normal.

 

Benchmarks are placed by the government, and land surveyors, and would me more accurate.

 

That being said, every device has a margin of error, so that is normal.

 

Scott

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quote:
Originally posted by McKenzie Clan:

If you reallt want to check it out, go find a local Benchmark.

 

Geocaches are placed by humans with the same type of devices as you, therefore margin of error is normal.

 

Benchmarks are placed by the government, and land surveyors, and would me more accurate.

 

That being said, every device has a margin of error, so that is normal.

 

Scott


 

One important note here--benchmarks are usually posted using a different datum than geocaches. WGS84 for caches, and NAD83 for benchmarks. Your owner's manual will have info on how to check, and change, the datum you are using.

 

Speaking of the datum used, if you are using the wrong one, it can cause everything to be shifted by a similar amount. Although 30 feet doesn't sound significant.

 

Another trick I learned a while ago: when my GPSr reads less than ten feet I put it in my pocket and just start looking. The GPSr doesn't point at the cache, just a point in space. After you get a few caches under your belt (not very many), you will start developing an "eye" for hiding spots.

 

Good luck,

Dave_W6DPS

 

My two cents worth, refunds available on request. (US funds only)

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quote:
Originally posted by McKenzie Clan:

If you reallt want to check it out, go find a local Benchmark.

 

Geocaches are placed by humans with the same type of devices as you, therefore margin of error is normal.

 

Benchmarks are placed by the government, and land surveyors, and would me more accurate.

 

That being said, every device has a margin of error, so that is normal.

 

Scott


 

Before relying on a benchmark check the benchmark page to see if the location is scaled (not very accurate) or adjusted (very accurate). We have found scaled benchmark as far as a tenth of a mile away from the given coordinates.

 

John

 

*******************************************************

It's hard to remember that your primary objective is to drain the swamp, when you're up to your a$$ in alligators.

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88'! That's a big error, BUT there are few things to check:

1. Has anyone else logged similar difficulty in locating this cache? If so, the posted coordinates may need fine tuning.

2. Heavy tree cover can confound the best GPS out there. So can nearby reflective surfaces, such as cliffs or tall buildings. Anything that interferes with the GPS's ability to *see* the sky above can cause problems exactly like you're experiencing.

3. Is the datum setting in your GPS set to WGS-84? If it's set to something else, like NAD27, you will see a significant difference between the posted coords and your GPS coords.

 

Finally, kudos for sticking with the hunt until you found it. It sometimes takes a LOONG time to find a cache when the coordinates or the technology aren't up to snuff. The good news is that most of the time you can expect to be within 30 feet or so.

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A couple of thoughts...

First, sort of like everyone else has been saying, the person who set the cache could have been off 5 to 10 meters (15-30 feet) when they first set the cache in place. If you have the same margin for error on top of theirs...you could be dead-on or off up to 20 meters (about 60 feet!) So I recommend taking the others' advice and looking for possible hiding spots when you get within a certain distance.

One other thing that has worked well for me. Using Topozone.com (making sure you use the correct datum and coordinate format of course) I found a road intersection by my house, zoomed in pretty close. Holding my mouse cursor over the map gave me the coordinates; then I just walked outside to the road intersection and took my own set of coordinates. They were VERY close. It is a pretty good way of checking your GPS.

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I bought a sportrak in September. After much frustration we finally figured out that if we added .020 to the west co-ordinate (which is about 70 of my paces) we would be very close to the cache. When my friend got her gps we discovered that this was a constant error. Rather than fighting with it I returned it to the store got a brand new replacement and now the coordinates are dead on.

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I have a Magellan Gold. Brand new. I went to an NGS adjusted benchmark, stood over it for 10 minutes. I INITIALIZED the unit there. This is on a lookout tower. I had 9 satelites with full bars. Stood there another 10 min, and it told me I was N.004 and W.004 away. I had it set to Lat/Long and Nad83 on both primary and secondary co ordinate systems. There were two other adjusted Benchmarks within 100 feet and it couldn't get me close. I created a waypoint to a cache site near a lake, and it shows it out in the water on the firmware map. It takes me back to my created track points quite well though. And can anyone tell me how the primary and secondary co ord systems are supposed to work. If one is set Wgs84 and the other is Nad83 which is it useing? Thanks in advance.

 

Physician heal thyself.

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I have a Magellan Gold. Brand new. I went to an NGS adjusted benchmark, stood over it for 10 minutes. I INITIALIZED the unit there. This is on a lookout tower. I had 9 satelites with full bars. Stood there another 10 min, and it told me I was N.004 and W.004 away. I had it set to Lat/Long and Nad83 on both primary and secondary co ordinate systems. There were two other adjusted Benchmarks within 100 feet and it couldn't get me close. I created a waypoint to a cache site near a lake, and it shows it out in the water on the firmware map. It takes me back to my created track points quite well though. And can anyone tell me how the primary and secondary co ord systems are supposed to work. If one is set Wgs84 and the other is Nad83 which is it useing? Thanks in advance. icon_confused.gif

 

Physician heal thyself.

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I have a new Magellan Gold. I have accuracy problems cacheing. I went to a lookout tower in the area that had 3 adjusted NGS markers. I picked the one on the tower and stood over it for 10 min. Then I initialized the unit with the NGS co ordinates. I stood there another 10 min an it told me I had moved the equivalent to N.004 and W.004. It could not locate the other two (adjusted) Benchmarks reasonably either. I had Primary and secondary co ord systems set to Nad83 & Lat/long, deg/min.mmm Also, how do the primary and secondary systems work? If one is set to Wgs84 and the other to Nad83 whats going on?

 

Physician heal thyself.

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