eTrex users -- Do you have the same experiences?

[Guest forbesRus]

I purchased an eTrex a few weeks ago and found a few caches. When I find the caches it indicates that I am 40-60 feet away, even when the unit indicates that the accuracy should get me to within less 20 feet. In all instances I have been in the woods and in some cases have been in ravines that might have contributed to the problems. Do any other eTrex users have the same difficulties? Is greater accuracy achievable with other hand held GPS units?

[Guest mcb]

That sounds just a little high but not unreasonable. The EPE number an eTrex gives you is only an estimate. You said that you were off by 40-60 ft. from the caches position. Well if the person that marked the cache had a EPE (Estimate Position Error) of 20 ft and you have an EPE of 20 ft you could in theory be off by 40 feet. For example the cache placer could have been 20 feet north of the actual position any you were off by 20 feet to the south of the actual position.

 

You also have to realize that the EPE in most Garmin units is only a 50% confidence number. This means that at any instant there is a 50% chance that you are with in the EPE value of the position show. To have a 95% confidence you would need to double that number. Check out http://joe.mehaffey.com/errors.htm for a little more on the error number from GPS units.

 

Also the geometry of the satallite will effect the accuracy of you GPS. It you are in a valley like you said then your veiwable satellites are closer together above you. This make the geometry worst and will add more error to you readings.

 

Hope this helped

mcb

[Guest gstrong1]

Yes, sounds familiar. I've gone out on 4 cache hunts while monitoring both my Garmin III Plus & my eTrex Vista simultaneously. On all 4 occasions, the eTrex, while at the cache, had me off by anywhere from 20 to 70 ft., while the III Plus had me within 15 ft. on all. After setting the eTrex down at the cache, after anywhere from 1 to 3 minutes, the eTrex would settle down & give me roughly the same numbers that the III Plus had given me upon arrival. All 4 cache areas were wooded, so I attributed the discrepancies to the internal antenna on the eTrex vs. the external antenna on the III Plus.Also considered that it might be the units power, 2 half run down aa batteries compared to the III Plus's 4 batteries. Not quite sure but when I go out on a hunt, the III Plus is the unit I depend on to get results. I'm getting too old to be running around in circles chasing false numbers.

 

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Gary "Gimpy" Strong

Rochester,NY

[Guest Quinnow]

antenna for it.

 

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Quinn Stone

Rochester, NY.14616

www.Navicache.com

 

[This message has been edited by Quinnow (edited 01 May 2001).]

[Guest Quinnow]

antenna for it.

 

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Quinn Stone

Rochester, NY.14616

www.Navicache.com

 

[This message has been edited by Quinnow (edited 01 May 2001).]