GPS accururacy

[+mountainmansamiam]

Hi there,

I'm from extreme southeastern Michigan and have a Garmin eTrex. I can stand in the middle of a field on a clear day and can only get down to 16 feet accuracy. Unit is about 5 years old. Can newer units do better? How close can you get on a good clear day? Sam

[+team140]

While doing some side by side comparisons for a GPS class I am putting together, my GPSMAP 60CSx showed 9' accuracy and the eTrex H showed 7' accuracy. An old 1st gen eTrex showed 51' accuracy.

 

Yes, the new ones are more accurate.

[+gmcpower98]

I had similar reception with my etrex

[+StarBrand]

No - not really.

 

Keep in mind that the number you are seeing is called an EPE (Estimated Postional Error). While Garmin is vague about the exact formulation - you should read it like this: "Given the current satellite constellation and signal strength, I would estimate that the current reading is maybe about within 16 foot of the actual coordinates - at least under these same conditions 60% of the time"

 

The newer units perform this calculation far faster with spiffy graphics and options and more sensitive recievers allow you to do it under more adverse conditions but in the end that number is only a guess. The unit has no actual idea of the true error - or it would correct for it.

 

The signal and math for the coordinates has not changed a bit wiuth SA off.

 

(Of course WAAS readings will somewhat improve the accuracy but it has been around for a long while now too)

[Birder579]

The way I checked the accuracy of my GPSr is to find a benchmark with ADJUSTED coordinates. It would help if there is a clear view of the sky at the benchmark. The ones with SCALED coordinates are not useful. Then hold the GPSr over the benchmark and average the reading for 5 minutes. Do this several times a day at different hours and you will get an idea of how accurate the GPSr is.

[+StarBrand]

The way I checked the accuracy of my GPSr is to find a benchmark with ADJUSTED coordinates. It would help if there is a clear view of the sky at the benchmark. The ones with SCALED coordinates are not useful. Then hold the GPSr over the benchmark and average the reading for 5 minutes. Do this several times a day at different hours and you will get an idea of how accurate the GPSr is.

Just make certain you are using the same datum as the reading on the benchmark.

[+slate6715]

I have a Garmin eTrex and found it to be very accurate when it gets a clear view of the sky. It does not handle mild canopy, canyons, or putting your hand over the top very well. I think the antenna is not as good as other GPS so the reception can be problematic.

 

I also have a Garmin Forerunner 205 that has excellent reception and can handle pretty thick tree canopy before it starts having problems. However, both have been spot-on with good signal on finding caches (in most cases).

[+Headhardhat]

There has to be some unseen factors not normally known when it comes to Etrex units. I have seen differences with

- varied battery strength

- how hot the unit is (sitting in a hot car or in the sun for extended periods of time

- cloud / canopy cover

- some software issues (like right before the date suddenly changes to 1964)

- if the wind is blowing to the east and Jupiter aligns with Mars.... Okay maybe not that bad but some times...

 

So I am not surprised with the differences. I just consider it a challenge which is part of the game.

 

Wonder if the $500.00 Colorados do the same thing?

 

-HHH

[Mag Magician]

I have 2 Blue Etrex units, one GPSMAP60, and a GPSMAP60cx. All will get me to within a reading of 15' accuracy in clear weather with no cover. Only the 60cx will give me an accuracy reading of less than 5 feet under a tree canopy. My conclusion is that yes, newer is better, but also antenna, programming, and cost are also factors.

[+ianafraser]

Depends on the conditions. Best I've received with my Magellan Explorist 500 is 2 meters. I usually give about 10 meters or so leeway when looking for a cache though. You never know what GPS was used & the conditions when it was marked.

Edited September 21, 2008 by ianafraser

[+WalruZ]

Commercial GPS units will pretty much always give you an epe of at least 15 feet no matter how much sky you can see, which has more to do with the limits that the technology is operating under than anything else. What the newer units can do is give you a good reading in less-than-perfect conditions. An old yellow Garmin will give you as good a position as anything if you're standing out in the middle of a field (where there is unlikely to be a geocache.) Walk it into the treeline or the woods and you'll get significant position degradation from multipath or foliage, and in thick canopy you won't have a position at all. The new yellow Garmin 'H' series will give you excellent position even in the treeline and can give you very good position even under thick canopy. It's what I've been using and I'm very pleased, and only $100.

[+Dread_Pirate_Bruce]

Just remember that even if you have a survey quality GPS that will give 1/4 inch accuracy, you are still at the mercy of the GPS used to hide the cache.

[Skippermark]

Not directly related to the OP's question, but when it comes to actual distances, we've seen distances vary between GPSs that are the exact same model.

 

Yesterday, my GPS had me 60 feet from a cache when it was found but a friends said he was just 17 feet away.

 

When we're walking with a group and are 1/4 mile from the cache, everyone walks the same direction towards the cache, but when we get to around 150 feet away, the group fragments with people going all different directions because everyone's GPSs is pointing in slightly different areas.

[+nekom]

my etrex legend C on the clearest of days tells me I'm +/- 7 feet. Of course, that's just its guess.

[+woffles]

Have you updated the firmware in your Etrex to the latest also if possible? My old Etrex Legend will show accuracy of 7 feet in good conditions.

[+greg1701]

just wondering how others felt about this...

 

If your GPS takes you within 2 feet of the cache, is it then too easy?

 

My point I guess is, I enjoy being within 30 feet then figuring out the puzzle. Ones that take me right up to the container, whatever, are kinda boring.. I enjoy the hunt...

 

Thoughts?

[+StarBrand]

just wondering how others felt about this...

 

If your GPS takes you within 2 feet of the cache, is it then too easy?

 

My point I guess is, I enjoy being within 30 feet then figuring out the puzzle. Ones that take me right up to the container, whatever, are kinda boring.. I enjoy the hunt...

 

Thoughts?

The cache coordinates on all tradtional non-puzzle caches should be as good as you can get them. Given that our units average 20 - 25 foot accuracy for both hider and finder - 2 foot for all cachers seeking a cache just isn't going to happen.

 

I don't do this to be challenged or puzzled. I do it to find caches and interesting locations.

[tubby and]

I also like to only rely on the GPSr to get me into the area. Then I like to rely on my ability to see the foot and a half square pile of parallel sticks.

[Motorcycle_Mama]

Yes, the coordinates for Traditionals should be as accurate as possible. Coordinates should not be intentionally posted incorrectly just to "increase the challenge".

[+Wild Thing 73]

16 feet accuracy in the middle of a Field>????????????????That is very good, but why are you standing in the middle of a field with nothing to do, but check accuracy of a GPSr. Take it to the woods, to a large dam, to a complex bridge construction. I think you are about a lot of doing nothing that makes no sense. You should be out Geocaching and getting your count numbers up. Placing a few caches...doing something for the geocaching community. It is called payback. On the other hand may I recommend you buying a Garmin Map 60Csx, then your accucary would come down to maybe 15ft....Or just remember, there is no such thing as accuracy in a handheld GPSr. The Government would not allow it....Or, we have what we have and that is it. Happy Trails,

[+greg1701]

Yes, the coordinates for Traditionals should be as accurate as possible. Coordinates should not be intentionally posted incorrectly just to "increase the challenge".

 

I wasn't inferring that I was doing that... I try to make them as accurate as possible. But if a person logs on your cache "coords off 20 feet" as if this was a high crime it seems silly.. isn't 20 feet close enough? As the other person who posted above "to find a pile of sticks placed parallel over a cache"...

[Whacked]

I had to laugh when I read what someone posted for a TB coords near my area.

 

"Coords were taken with my Garmin GPSMap 60CSx so the coords could be off as much as 5 to 6 inches."

 

Still gives me the chuckles. Obviously this person is oblivious to the capabilities of his GPSr.

 

There is no way a $300 GPSr will give better coords than a $3000+ surveyors GPS or better than Military Grade.

 

Best you can hope for is 3m accuracy in percect conditions

[+Crow-T-Robot]

My point I guess is, I enjoy being within 30 feet then figuring out the puzzle. Ones that take me right up to the container, whatever, are kinda boring.. I enjoy the hunt...

 

I'm not a numbers cacher but if I end up in a park that has 10 caches in it, I want to hit them all before the day is out. It doesn't seem like a big number, but a 30' difference in coordinates can add a significant amount of time to any hunt and it increases the frustration level accordingly. There's only so many times that I'm willing to get scratched by thorns or blackberry brush, to have a branch reach out and snag my shirt or grab the hat off my head or to get the dreaded face whip from a branch that slips out of my hand before I give up on the hunt. Not to mention the sweat, mosquitoes, mud, bugs and pine sap. All those things, I'm willing to put up with for a well-hidden cache, but not so much just because the coordinates are off.

 

Bruce

[+Cstandi1]

Just to be clear, clout cover makes little to no difference to GPS reception the frequency chosen for GPS was chosen specifically because weather has almost no effect on it. Also trust me, military GPS are no more accurate than any of the receivers that civilians have. I would rather have a good mapping civilian GPS than the plugger that the Army gives me, most are so old that they dont even have good high sensitivity receivers.

 

"Or just remember, there is no such thing as accuracy in a handheld GPSr. The Government would not allow it"

and the government no longer regulates the GPS frequency spectrum. The opening up of all GPS signals to civilian use in 2000 was what actually allowed geocaching to work, before that no handheld GPS was accurate enough to work because the government did interfere with the signal back then.

[gerboa]

just wondering how others felt about this...

 

If your GPS takes you within 2 feet of the cache, is it then too easy?

 

My point I guess is, I enjoy being within 30 feet then figuring out the puzzle. Ones that take me right up to the container, whatever, are kinda boring.. I enjoy the hunt...

 

Thoughts?

 

1000% Right....

[+frex3wv]

What I tell newbies is - "when your gps gets you to within 30 feet - start looking around for the cache in a 30 foot radius." That works. For me - the fun is seeing just how close my gps can get to the actual posted coordiantes/cache hide. Its always cool when your gps sais 1 foot when you are a foot away from the cache.

 

In other words - accuracy of 30 feet and lower is just fine for geocaching.