Cacheing Accuracy

[Bifter]

Hi everyone. I live in the u.k and am new to caching. I am going to my first cache tommorrow. 01.01.04 Just a few questions to ask.

 

1) I have a basic etrex when the sats lock and it says acuraccy 20ft does this actually mean that the unit will get me to within 20ft of the inputted waypoint?

 

2) When people post cache co-ordinates how accurate are they in general. I have read stories of getting as close as 100 meters. How are you supposed to find a cach if you only get within 100meters?

 

3) I did a lot of research before buying the etrex, can anyone tell me just how close they can get me to a cache?

 

Many thanks to anyone who takes the time to answer my questions.

[+WeightMan]

Do remember that the person placing the cache was also using a GPSr that has a similar error. Also that error reported by the machine is ESTIMATED. Your mileage may vary. It is always hoped that the two errors will cancel out, but sometimes they add together. Figure somewhere around 15-20 meters maximum error as a starting point. Most of the time the error will be less than that and usually near the 7 meter point.

[+Sparky-Watts]

I use an ETrex Legend, and have been able to walk directly to the cache with it on pretty much all of my hunts. Usually within the last 15 to 20 feet, I no longer look at the GPSr, and just walk in the direction it was pointing me, guesstimating the distance, and have good success so far that way.

[+Kewaneh & Shark]

The recreational GPSrs we use, including your ETrex, have a general accuracy of 10 meters (35 feet). What this means is that your GPSr will get you to the proper coordinate, +/- 10 meters. At any given time, they are usually well within that measure of accuracy and are closer to about 4-7 meters. That's plenty close to find a cache. And, it's not uncommon to find a cache and have your GPSr show the exact posted coordinates.

 

The 100 meter accuracy was an issue BEFORE the Selective Availibility (SA) function on the satellites was turned OFF. When SA was on, the best a recreational GPSr could do was about 100 meters. With SA turned off, the accuracy error is decreased about ten times, to 10 meters. A GPSr with WAAS capability can cut the accuracy error in half again, down to about 5 meters.

 

Your ETrex is an excellent instrument. It's not my weapon of choice, but I've used them, (and was impressed) and have friends that cache with them without any problems. It should serve you well.

[+mozartman]

I, too, have been amazed at my Etrex Legend-- it generally gets me to within 10 feet of the cache... sometimes even within a foot of where the cache is!

Edited December 31, 2003 by mozartman

[+bons]

Include into that factor anything that blocks reception. In a steep valley between tall hills I've watched my GPSr jump around, sometimes by over 50'. Near extremely powerful power lines, getting an accurate lock is also close to impossible. And some people have said that the old timber in the Pacific Northwest can play havoc with their GPSr.

[+DomHeknows]

we don't get waas in the uk do we????Enjoy your first cache (of many I hope!)

[Bifter]

I have it on good authority that waas will be fully enabled by second quarter 2004 CoooooooooL!!!!!!

[Bifter]

Whoops I just realised my etrex isn't waas enabled LOL....

[Bifter]

As you can see i'm coming to terms with the forums I now have an avatar and a signature........

[+Sparky-Watts]

As you can see i'm coming to terms with the forums I now have an avatar and a signature........

Ummmmm......I don't see either!

 

Try, try again!

[Kerry.]

we don't get waas in the uk do we????Enjoy your first cache (of many I hope!)

WAAS specifically No, but EGNOS is the European version that should? give coverage in the UK.

 

Cheers, Kerry.

[Bifter]

Hi Kerry! I know you have to have a waas enabled handset to recieve waas but what about this egnos? is it the same or does any set recieve this?

[+GeckoGeek]

sometimes even within a foot of where the cache is!

That's a good trick considering that there aren't enough digits to get you closer then the nearest block of 6' x 6' (actual size depends on how far from the equator you are.)

[+Renegade Knight]

Walk with wise persons and you yourself will become wise, but walk with fools and you will fare badly!!!

 

Isn't this a paradox? The wise will shun the foolish lest they fair badly, and the foolish will remain so forever. Nobody wins, and the human race gets more idiotic over time. Nevermind, that resembles real life.

Edited January 1, 2004 by Renegade Knight

[+KerryG]

I think most people will tell you their experience is that any of the modern units are usually more than adequate. I use an older Garmin eMap and more often than not the coords are within 5-7 FEET of the cache. The worst I have had was a cache 50' from the coords, and most of the people who found it reported it 50' off as well.

 

In some cases, the GPSr was so dead on I couldn't believe it. One super-ultra-micro-cache I was looking for was off a trail, the eMap said it was 6' to my right and I swear had I measured it, it would have been 6' to the inch.

 

When I get to a location and having trouble locating a cache, I will often walk around for a couple minutes to get a decent average of the posted coords, then trust my device that I am standing within 10 feet of the location. That has only failed me once so far as I mentioned before.

[Kerry.]

Hi Kerry! I know you have to have a waas enabled handset to recieve waas but what about this egnos? is it the same or does any set recieve this?

Both are compatible Wide Area Differential GPS (WADGPS), both work the same way just that the corrections are based on different ground stations.

 

In Europe EGNOS = WAAS, just a different name and operated/provided by different organisations.

 

Cheers, Kerry.

[+mozartman]

sometimes even within a foot of where the cache is!

That's a good trick considering that there aren't enough digits to get you closer then the nearest block of 6' x 6' (actual size depends on how far from the equator you are.)

it IS a good trick, then , I guess! There have been a lot of times where the coordinates are right on and all I have to do is reach a little ways up or down and the cache is there! In fact, I think I'm spoiled because most caches are within a couple feet of the coordinates and I don't usually have to search too much at all... spooky... or lucky...

Edited January 1, 2004 by mozartman

[+Sparky-Watts]

sometimes even within a foot of where the cache is!

That's a good trick considering that there aren't enough digits to get you closer then the nearest block of 6' x 6' (actual size depends on how far from the equator you are.)

it IS a good trick, then , I guess! There have been a lot of times where the coordinates are right on and all I have to do is reach a little ways up or down and the cache is there! In fact, I think I'm spoiled because most caches are within a couple feet of the coordinates and I don't usually have to search too much at all... spooky... or lucky...

I've been able to do the same thing a number of times. The only few times I haven't been able to get within a foot or two was under heavy tree cover.

[Bifter]

Found my second cache today, (first yesterday) one was in the open and one was heavy trees even though no leaves cos its winter. However on BOTH occasions I have been within 10feet of the cache and I only use a basic Etrex. I have only done the 2 caches though so maybe im on a roll. LOL

[JDzags10]

I have an basic lowrance ifinder. I havent had much experience with it so id like to know how accurate it is if anyone had any idea.

[+JayFredMuggs]

My Etrex Legend has been right on on two occasions, showing 3 ft. when at the cache location. I have also had the cache container in my hand and my Etrex said I was 91 ft. away. It all depends on the strength of the satellite fix that you have at the time, and the strength of the satellite fix that the cache owner had on the day it was placed. Many folks will carry more than one unit and average the coordinates. When I get to within 25 ft or so, I don't rely on the unit for direction. I just start looking around.

One difference is when benchmark hunting. Many of the benchmark coordinates are not very accurate. Keep in mind that many benchmarks were first surveyed in the 1930's and 40's using conventional methods. I have found some benchmarks to be off by as far as 250 ft. from the published coordinates.

Edited January 4, 2004 by JayFredMuggs

[Bifter]

Hi JD I have done a bit of research on the lowranse ifinder and it seems to be a straight-forward 12channel gps.....whiche means if you get a decent lock on say 5or6 sattelites you should get accuracy within about 20ft.......happy caching......Bifter.

[rameous]

I have an Etrex Legend and have gotten really close 10 or 15 feet, however you should consider the accuracy of not only your GPS but the GPS that was used in placing the cache. ~ 30 to 50 foot margin of error

[+Night Stalker]

The majority of caches I have found have been well within 20'.

There is always an exception. One cache was more that a half mile off. The only reason we found it was that some other poor cacher had traipsed all over those hills, found the cache and left corrected coordinates. Whenever I do find a cache that is not within a reasonable distance from zero I notify the cacher of my coordinates so he can check it out. I also request other cachers do the same on my caches in case my GPSr has a bad day or I scrambled some of my numbers.

 

[Prof. Y. Lupardi]

I, too, have been amazed at my Etrex Legend-- it generally gets me to within 10 feet of the cache... sometimes even within a foot of where the cache is!

Here on the European continent we have different feet. In this time of the year we have cold, wet and muddy feet.

I place my caches with the help of the good old GPS12. Mostly I use the local grid for coordinates. This grid is in meters. I average the position for 15 minutes and at that moment the numbers on the display (giving meters!) are stable.

Some of my caches I could double-check with digital topographic maps with a granularity (pixel size) of 2.5 meter. And my measured position was always right on the spot (on the pixel).

Should a surveyer measure my caches I am at the most 2.5 meters wrong!

 

Another question is: when someone comes looking for a cache with an EPE of say 12 m(eter) and the accuracy of the cache position is know with about 10 meter accuracy, what is the probability of being within 2 meters of the cache?

Is there here a mathematician?