GPS Accuracy

[+hammich]

I have been experiencing problems getting accurate readings with my GPS. I have a Garmin Etrex which I purchased about three years ago. I have put out two caches in the past month or so and have taken multiple readings to establish the coordinates. When other cachers have tried to find the caches, I have been told that the readings are placing them 50 feet or so from the cache. When hunting caches, I am frequently a number of feet off also. I realize there will always be some variance, but want my cache coordinates to be as accurate as possible.

 

I'm wondering about my GPS; is it faulty? Do more expensive ones give more accurate readings? Has there been improvements over the past three years? Should I invest in a new one?

 

Would appreciate any help. Thanks. Hammich

[+trainlove]

I have been experiencing problems getting accurate readings with my GPS. I have a Garmin Etrex which I purchased about three years ago. I have put out two caches in the past month or so and have taken multiple readings to establish the coordinates. When other cachers have tried to find the caches, I have been told that the readings are placing them 50 feet or so from the cache. When hunting caches, I am frequently a number of feet off also. I realize there will always be some variance, but want my cache coordinates to be as accurate as possible.

 

I'm wondering about my GPS; is it faulty? Do more expensive ones give more accurate readings? Has there been improvements over the past three years? Should I invest in a new one?

 

Would appreciate any help. Thanks. Hammich

 

You can upgrade but don't need to. But always look at your EPE estimated position error whe recording waypoints, the smaller the better.

 

GPS system accuracy, 10 meters 1 sigma for you plus 10 meters 1 sigma for a cache finder.

Some GPS's have firmware issues and will give wrong readings if you just stopped moving (see somewhere in my profile).

 

Some GPS's might actually be slightly off in time, display time not GPS time, and this might cause 100-200 yards of error until the user figures out this problem. Also in that hints page. To check your time, listen to shortwave radio or go to the atomic clock site in Boulder, or compare the clock on your GPS to a Garmin that's on and receiving satellite signals (since yours is a Garmin it should be OK once it reads the sats).

 

As an experiment, keep your GPS off for a week. Turn it on and immediately compare the clock to your watch, make not of the difference. Once the satellites get picked up compare to you watch again and note the difference. A GPS will drift 10-20 seconds a week but a Gramin resets itself, not so lucky with Magellans.

[+Cornix]

... I have been told that the readings are placing them 50 feet or so from the cache. When hunting caches, I am frequently a number of feet off also.

Is your unit set to NAD27 datum? You should use WGS84.

 

Cornix

[+JSWilson64]

When you say you have taken multiple readings, have they been at different times/days? That's one thing to try - go 2 or 3 times in one day, record coords 3-5 times each visit. Repeat on 2 or 3 separate days.

 

Another option might be to find a local cacher with a more sensitive unit, and borrow it to place your cache.

[gallet]

accurate readings? Has there been improvements over the past three years? Should I invest in a new one?

 

Would appreciate any help. Thanks. Hammich

 

Why don't you test it yourself to see how accurate it is?

 

Use www.maps.google to find a road interdection near you, click the intersection to centre it and big it up, grab the coordinates then check it with your gps.

Edited December 14, 2007 by gallet

[+Renegade Knight]

It's hard to say. The cache I got complaints about had issues.

 

It was under a tree. (Multi path errors, plus flat out blocking the signal).

It was at the base of a small cliff in a large crack (more multi path errors)

All of that was under very high voltage power lines. I'm not sure what kind of error power lines cause but they do screw up your signal when you are under them.

 

Everbody complained about my coordinates.

 

If you have not had problems in the past, maybe you have a locaiton that causes probems with signals.

 

I've seen problems with tall buildings, Bridges with a metal superstructure, cliff's, trees and power lines.

[+Prime Suspect]

I have been experiencing problems getting accurate readings with my GPS. I have a Garmin Etrex which I purchased about three years ago. I have put out two caches in the past month or so and have taken multiple readings to establish the coordinates. When other cachers have tried to find the caches, I have been told that the readings are placing them 50 feet or so from the cache. When hunting caches, I am frequently a number of feet off also. I realize there will always be some variance, but want my cache coordinates to be as accurate as possible.

 

I'm wondering about my GPS; is it faulty? Do more expensive ones give more accurate readings? Has there been improvements over the past three years? Should I invest in a new one?

 

Would appreciate any help. Thanks. Hammich

Are you current on your OS releases?

[+trainlove]

accurate readings? Has there been improvements over the past three years? Should I invest in a new one?

 

Would appreciate any help. Thanks. Hammich

 

Why don't you test it yourself to see how accurate it is?

 

Use www.maps.google to find a road interdection near you, click the intersection to centre it and big it up, grab the coordinates then check it with your gps.

 

I don't know about you, but I have absolutely NO confidence in any electronic maps. Not those MapSend Topo's in my Magellan (1CD all USA), or MapSource Topo in my Garmin (3CD all USA) or National Geographic BackRoads Explorer Topo (17CD's all USA, plus 2 CD's all New Hampshire + 2 CD's Mass & RI), or Delorme Topo (6CD's all USA) or any others. Street data has been collected years ago with no consistancy, no procedures for accuracy, no mention of map datum and EPE of system used to collect data, just plain nothing. Plus I wouldn't want to stand in the middle of an intersection.

 

P.S. Just got Maptech Terrain Navigator Topo (17CD's all New England and New York) can't say much yet if it's great, but it's made from existing Topo paper maps so well there you go, the data is 20-40 years old and NAD27....