Garmin Etrex (yellow case) - Just how accurate is it?

[leighheppell]

I Just purchased the Garmin Etrex, and went out for a test. Parked the car, fired up the GPS, and hit enter to create a way point. Then did a 4 mile walk, (at appx 2 miles i selected the waypoint to goto) It a circular route so should take me back to the car. Well I got to the car, and the gps said i have another 120ft to travel. Is this normal or is there a fault??

All help gratefully received.

[+brdad]

It is possible to be off that much. The biggest factor would probably be the accuracy the Etrex had when you made a waypoint where the car was and the accuracy when you returned.

 

If you go to the satelite page on the Etrex, at the top is says Ready to navigate. Accuracy XXX feet. If you had 24 foot accuracy when you made the waypoint, and 45 foot accuracy when you came back, you could be, in theory, be off by 69 feet (24+45). It would be quite a cooincedence that you would be the max accuracy off on both occasions, but who knows...

 

On average, my Etrex gets me a lot closer than that, I'd guess 30 feet or so.

 

We all have mental problems, it's just that some of us choose to show them.

[leighheppell]

Just another thought, I am in the south west of UK (Cornwall) and have the map datum set to WGS 84, is there any way i can tell if thats the best setting? - outside now its give an accuracy of 33ft?

[+MacBWizard]

I used to own a yellow eTrex and generally it would work much better than what you describe above. When navigating back to one of my waypoints it would be off by about 20-30 ft. Make sure you have pretty good accuracy when you set a waypoint. I had on occasion had the accuracy on the yellow eTrex to be 100ft for a few minutes when it powers on. If you didn't wait a few minutes, especially after you turn it on for the first time, the gps will have pretty bad accuracy. I would test the unit again and see what happens. By the way, the eTrex series likes to be held horizontally the way the antenna is oriented, and that might give you better reception.

 

Oh, and changing the datum will not affect accuracy.

[+brdad]

MacBWizard201 is right - the datum won't affect your accuracy.

 

The datum gets important when you are transferring waypoints from somewhere other than your GPS, like from maps or waypoints downloaded from geocaching.com. Not having the datum right there can throw you off considerably.

 

We all have mental problems, it's just that some of us choose to show them.

[leighheppell]

This accuracy thing is very worrying, consider snow, white out, gulleys/ravines left or right, with an accuracy so poor where do you go?

 

I have just looked at:

Magellan Meridian GPS

 

This can use the EGNOS system which boasts a greater degree of accuracy.....

 

Its loads more money, but does anyone have any experience/views on this model??

 

[Gnomon]

and it ws always better than that, although errors of 20-50ft were not unusual

 

~Glenn

[+MountainMudbug]

I have a yellow etrex and it does vary in accuracy, especially in foul weather under rain-dampened trees. That's to be expected occasionally, but for the most part it seems to get me right into the cache zone, which I consider to be a 30-50 ft radius. Sometimes it is dead-on right. There's also the accuracy of the cache-hider to consider, maybe their coordinates were a smidge off when they placed it - that happens sometimes too.

I always take along the Hint on the cache's page (if there is one) - it should get you the rest of the way to the box if you are stumped and feel you're not getting an accurate enough reading on the GPS.

Found four caches yesterday, one was 3.4 ft off - that's not too shabby!

Mudbug

 

_________________________________________________________________

I'm afraid I have no choice but to sell you all for medical experiments.

[+Searching_ut]

One thing they don't mention in the instruction manuals is that virtually all consumer GPS receivers I've tried are often off by a fair amount when they first lock on. If you've had a significant altitude change since the unit was last on, the receiver can be off by quite a bit for awhile. If you view the tracklog you'll often see the unit got an initial fix, then more or less slid into a more accurate position of the course of a couple of minutes. I always leave the unit on for a few minutes prior to saving the waypoint, and have found this helps a great deal. As for the Estimated position error the unit reports, it may or may not be of any help. I've found it somewhat reliable in good reception conditions, but there are a lot of variables the unit can't detect, which make it's accuracy guess less reliable especially in poor reception areas

 

For what it's worth

 

Jeff

[leighheppell]

I Have taken onboard all your comments, and will either bin etrex, upgrade, or not bother at all!

 

I mistakenly thought these units were fair accurate, but up the 30ft off target is a joke for serious off road tracking, or skiing in a white out.

 

If you know of a better accurate unit, please let me know

 

leigh heppell

http://www.exotic.co.uk

[+MacBWizard]

I own an eTrex Vista that I have found to be a little more accurate than the yellow eTrex. I have heard good things about the reception of the Garmin 76 and 76s units that have a different, more sensitive antenna than the patch antenna in the eTrex units. Also look at the Garmin GPS V which is supposed to have good reception, but I have seen some controversy over its accuracy. Having not tested either the 76 or GPS V, I am only going off of the specs of the products and what I have read here. Hope that helps.

 

oh, and by the way- I don't think any unit would be able to get very good accuracy in a white out.

Navigating back to a waypoint and being 30 feet off on your gps when you arrive is not bad. That accounts for 15ft accuracy when you set the waypoint, and 15 ft. accuracy when you arrive at the waypoint. Without WAAS (which is also controversial about its effects) or an external antenna this is great, in my opinion, for an eTrex. If you need better than an eTrex look at this thread-Trimble PRO XR

 

[This message was edited by MacBWizard201 on October 19, 2002 at 03:01 PM.]

 

[This message was edited by MacBWizard201 on October 19, 2002 at 03:02 PM.]

[Kerry.]

quote:

---

Originally posted by Pusher of Clay!:

.... I mistakenly thought these units were fair accurate, but up the 30ft off target is a joke for serious off road tracking, or skiing in a white out.

......

---

 

Depends on what you think "fairly Accurate" is as up to 30 feet (even 40 feet) is well within the specifications of the system.

 

As with WAAS, EGNOS is not all the answer either and still has some way to go to be fully operation as well.

 

So not real sure what you were "expecting" but sounds like it might be an over expectation.

 

Basically regardless of the consumer grade receiver at this level one still needs to understand and work within the specifications of the system.

 

Cheers, Kerry.

 

I never get lost everybody keeps telling me where to go

[+Stunod]

Are you sure someone didn't move your car?

 

Just being a smartass...

 

"Just because I don't care doesn't mean I don't understand."

[+kevin917z]

that seems really bad, after letting my yellow etrex acquire all satellites, i have got the accuracy down to 11 feet numerous times, when it was hooked to the laptop allowing more decimal places to be shown with software it read 11.27 ft accuracy, my average accuracy is around 12-15 feet, dont know why yours would be off so much

[+Searching_ut]

When discussing accuracy, remember that the Estimated accuracy number given by the receiver is just that, estimated. The only way you can figure out how accurate the unit really is at that moment is if you're doing the reading at a known location.

 

Estimated accuracy numbers have gotten smaller with recent upgrades to the eTrex series, and several other receivers recently. I haven't seen any change in the "real" accuracy however. Marketing ploy, or does the software better reflect the real accuracy the unit is getting. That's something only "they" know for sure

 

For what it's worth

 

Jeff

[Dinoprophet]

I wouldn't stake my life on the yellow eTrex if I needed better than 50ft accuracy to live, but for finding caches, it's worked perfectly fine. Many cachers use them, and in my experience, the inaccuracies are usually reproducible, i.e. if the hider's yellow was off due to tree cover, mine is likely to be equally off in the same way, hence I've found some caches faster than someone using a much more accurate unit.

 

[+briansnat]

120 feet off sounds like a bit much, but possible depending on the conditions at the time. 20-50 feet can be expected with any consumer grade GPS, whether its Magellan, Garmin, Lowrence or whatever. Military and "industrial" grade GPSr's are considerably more accurate, but they cost thousands of dollars.

 

"Men don't stop playing because they get old, they get old because they stop playing" Oliver Wendell Holmes

[ikayak]

quote:

---

MacBWizard201 I used to own a yellow eTrex and generally it would work much better than what you describe above.

---

 

I am the new owner of MacBWizard201's yellow and he is right, I am consistantly getting great accuracy readings with it. In the open I usually get in the 17-24ft range and in semi-tree cover it got 25-37ft on a recent find. Close enough that I nearly tripped over the cache. Can't beat that!

 

Though...your mileage may vary.

 

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

Quote me as saying I was mis-quoted.

[+kevin917z]

just thought of something, battery save mode could and can cause slight accuracy decreases too, 1sec update for normal mode 5 for battery save

[dogsoldier]

...and, it's never steered me wrong. I would still like to upgrade, but not because it's insufficient or anything.

[+Cachier]

I have a yellow Etrex. Their accuracy is greatly diminished by tree cover, overcast skys, obscuring terrain and poor antenna orientation. On cache hunts, its not uncommon to see the arrow swing around and the distance to destination jump from 3 ft to 65 ft in just a few steps as you lose lock on one satellite and retain lock on anothers. In open terrain with no trees, I swear by it. In forested locations, I swear at it.

 

"When you find it, its always in the last place you look."

[+apersson850]

quote:

---

Originally posted by brdad:

If you had 24 foot accuracy when you made the waypoint, and 45 foot accuracy when you came back, you could be, in theory, be off by 69 feet (24+45).

---

 

This is a common misunderstanding. Since the EPE (Estimated Position Error) is defined as a probability that you are within a certain circle, you cannot just add the EPE's. The correct sum above is 51 feet. It's calculated as the square root of the sum of the squares of the EPE's.

 

Also remember that the CEP (Circular Error Probable) which is calculated by the GPS, often is a 50% value. That is, there is a 50% chance that you are within that circle. Double the accuracy figure, and you are 95% certain. Read this thread for an in-depth discussion of the accuracy of a GPS.

 

Anders

[Deanster]

I only use the arrow till I get close (-100'). Then I look at the cords, side stepping.. one step at a time, till they match. Gets me closer the first time. (That's from my old Loran days. )

[+mrmom]

After finding that a cache coordinates are off by 50 or more feet, I'll email the owner to recheck and offer my coordinates taken by 2 GPSR's. I will also ask what type of GPSR they are using. 100% of the time, the owners were using the e-trex line. The units patch antenna will work well out in the open. In the woods; they're lame. While doing team finds, the cachers holding the e-trex are the ones searching furthest from the actual cache. There are no opinions expressed here. This is just what I have observed. One does get what they pay for.

 

Geonavigating since 1991

[+Siberian Cacher]

quote:

---

and the gps said i have another 120ft to travel. Is this normal or is there a fault??

All help gratefully received.

---

 

My first find on my little yellow etrex was within 3 feet. I turned on my unit well before I got to my inital starting point so it had about 5 minutes to warm up. Once I got to my starting point, I powered down and immediately powered up and then headed off. It took my right to the "treasure" and when I was standing right next to it, it said I was 3 feet away.

 

To me, that's pretty darn accurate. Especially considering the cache was the size of a roll or quarters and hanging in a tree! [smile]

[ikayak]

Since you're talking first finds with the yellow, when my yellow said "0" feet to waypoint, I was only 6.5 feet away from the cache. I'd say that's not too bad, eh!?!?!

 

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

Quote me as saying I was mis-quoted. - Groucho Marx

[+Katetrex]

I regularly download tracks and routes to my computer from the etrex and overlay them on maps and sometimes just for fun the aerial photo option. In all cases, I have found the etrex info to be very accurate matches to the maps. Yes, you do have to give the unit time to catch up to its exact position. This is delayed sometimes by obstacles to clear satellite signals or being turned off in one location and turned on miles away.

[sykonico]

And it works really good for me.

All the caches i found, it was with an accuracy of 10 feet or less. Except for 2 because a really heavy tree cover.

What i discovered, when you're getting close to the cache, slow down, take your time. Turn around and follow the arrow slowly. Your GPS will be grateful, having time to receive a signal before you go past the cache. Don't hesitate to repeat the approach.

And more important, don't forget you have eyes and hands, don't stay with your nose stuck on the screen.

 

42

[+kevin917z]

today i tested out the DGPS on my Yellow eTrex the best i could get was 5ft accuracy, the etrex shows a D on the signal bar and has Ready to navigate DIFF: xx ft didnt think i would get that good of results!

[+Cachier]

quote:

---

Originally posted by kevin917z:

today i tested out the DGPS on my Yellow eTrex the best i could get was 5ft accuracy, the etrex shows a D on the signal bar and has Ready to navigate DIFF: xx ft didnt think i would get that good of results!

---

 

In flat ole Kansas, you probably have 360° of flat ole horizon. How many satelites can you lock onto at one time? The more birds, the better the precision. How does differential GPS work with the Yellow etrex?

 

"When you find it, its always in the last place you look."

[Kerry.]

quote:

---

Originally posted by Cachier:

.... The more birds, the better the precision.

---

 

No

 

Cheers, Kerry.

 

I never get lost everybody keeps telling me where to go

[+kevin917z]

until 4-5 wks ago i was able to lock onto 12 sats at a time, now im like 10 11 or 12, dont know why

to use the DGPS on the garmin you have to have it set in the right interface and have one of several external objects hooked to it,(DGPS beacon, RTCM radio, or an internet connection), i was able to do this across an internet conn. that received RTCM/NMEA data from a Garmin GBR21 beacon i used both RTCM/NMEA and Garmin DGPS interfaces and they worked equally well

[+Cachier]

quote:

---

Originally posted by Kerry:

quote:

---

Originally posted by Cachier:

.... The more birds, the better the precision.

---

 

No

 

Cheers, Kerry.

 

I never get lost everybody keeps telling me where to go

---

 

OK, explain!

 

"When you find it, its always in the last place you look."

[Kerry.]

quote:

---

Originally posted by Cachier:

_OK, explain!_

---

 

Myth #1, the more satellites the better the accuracy. Also note "Precision" and "Accuracy" are 2 basically different (but related) things.

 

Accuracy has all to do primarily with geometry (relationship of the satellites to themselves and to the user) as a whole heap of satellites with poor geometry simply will give a poor (inaccurate) result.

 

Actually the more satellites used sometimes decreases the accuracy (even with reasonable geometry) especially low horizon sats which can introduce all sorts of errors in the position solution.

 

But essentially it's the geometry that matters far more than number of sats. A position solution based on minimum sats with good geometry (better still minimum+1) has far more integrity and reliability than from an over populated solution with poor geometry.

 

Cheers, Kerry.

 

I never get lost everybody keeps telling me where to go

[+Cachier]

It is my understanding that the accuracy of GPSr is improved by the analysis of multiple triangulation calculations from data provided by multiple satellites. Granted, there is probably a point of diminishing return where the increased number of locks don't the improve accuracy.

 

I would agree that, the farther out a satellite is toward the horizon, the less reliable the signal strength is due to distance and atmospheric conditions. Hence, it becomes an inconsistent contributor of data to the analytical algorithm.

 

The ideal scenario would be to have the most satellites possible within a 120° unobstructed view of the GPSr antenna. Since all of elements are variable to some greater degree, a moment of optimum accuracy is fleeting.

 

In my observations of the Yellow’s accuracy indicator, the best accuracy is obtained with the most number of locked satellites with a good strong S reading. Since all elements are variable, I guess we should be happy to achieve the minimal accuracy ratings published in the Garmin manual.

 

"When you find it, its always in the last place you look."

[+graylling]

I haven't found my yellow Etrex to be any more or less accurate than any other make or model.. Many times it's brought be to within 1 - 2 meters of a cache. One thing I do find is that it's accuracy when you are moving is less than if you are standing still. When I find a cache I'll just put the unit down and wait for a minute or two. During this time you can see the accuracy of the reading increasing until it's within a meter or two of the caches posted coords. Never had it anywhere near 120 ft off though.