New User 4 caches found Etrex 20 accuracy question always next to road?

[Geo J&Sly]

I used a combo of my phone and the new Etrex 20 to find a few caches. I bought the etrex 20 mainly for trail riding on my enduro and hiking, but geocaching is a nice way to get out and get familiar.

 

I bought a bundle and have the 100k maps from Garmin on a SD card installed and they show up.

 

I have noticed today that while driving down the road I showed up next to it about 10-15 feet off the side of the road.. This bothered me so I came back home and read and changed a few things and still my GPS shows me next to the road, not on it, still 10-15 feet next to it.

 

Is this because I have the topo 100 maps and need the 24k maps? Or is this an accuracy issue?

 

I have tried settings like:

. Lock on Road

I have changed guidance method

Calculate routes for pedestrain and car/motorcycle

 

Still I am next to the road.

 

Now on the geocaching I realize these are not always precise coordinates..

 

I did find one with precise coordinates locally GCJXE7 ( http://www.geocaching.com/seek/cache_details.aspx?wp=GCJXE7 ) that gives some precise coordinates for a "bonus find":

 

"find this location N42' 59.812 W084' 34.029"

 

I went there tonight and found the bonus..

 

I set my GPS right on it and it read:

 

N42' 59.811 W084' 34.029

 

So the coordinates seem to be accurate on this unit, or extremely close.

 

I have GPS + GLONASS enabled.

I have tried with WAAS on or off.

 

Here is my concern is this just an issue due to something faulty in the GPS? I can return and try a replacement or another unit if so. I dont want to show up next to the trails while riding my bike in the spring summer, that wont do me any good. I might as well just use my phone an locus, etc then.

 

Also on the caches if I am always 10-20 feet off it will make it more challenging.

 

Thanks for any insight. I am hoping there is an easy solution of either I need better maps or change settings, or reset or something.

 

If this is the improper place or website please feel free to suggest where I might find this answer or post the question.

Edited December 2, 2012 by Snake2715

[+Atlas Cached]

If you are using Garmin Topo 100K, you are lucky you can even see the road you are on! I have seen errors of more than 300 feet with Garmin Topo 100K, in highly populated metropolitan areas!

 

If you want to test your GPSr (I am very sure it is not the issue), mark a waypoint at a location you know you can find again, then copy those coordinates into google maps, and you will see the map on your GPSr is the issue, not the GPSr.

 

Try some maps from GPSFileDepot before you buy Garmin 24k maps.

Edited December 2, 2012 by Atlas Cached

[Geo J&Sly]

First thanks for the quick response, really appreciated!

 

Downloading a Michigan TOPO from GPSfiledepot now.

 

Ok So their maps are just not accurate potentially?

 

I did the waypoint, actually pulled up the satellite screen and stood still outside and took a reading. I typed that into google maps (not earth) and its about 2 car lengths off.

 

Is that where it should be? Thats actually about ow far off the road it was putting me...

 

Actually I checked the green arrow in google maps and it gives coordinates (after I typed my coordinates in) and they are not exactly what I type.. not sure how google maps stores its info so maybe its giving me a close set of coordinates.

 

Maybe I am expecting too much from the GPS? Its just December here and should be snowing so I wont get to use it for the main purpose until well after the return period expires.. just worried it wont work on the trails I downloaded.

Edited December 3, 2012 by Snake2715

[+Atlas Cached]

Your GPSr is one of the most accurate available today.

 

Your issue is completely with the maps you are using. Most maps are not as accurate as the GPSr you have.

 

What was your GPS Accuracy when you took a reading from the device? 7 feet? 13 feet? 32 feet?

 

Is that number about how far it shows you from where you actually were?

[Geo J&Sly]

Ok So I downloaded and installed the topo to basecamp, sent it to my GPS with the trail maps.

 

I walked outside and have an open area (by farmland) some trees to one side maybe 50 ft away.

 

In menu satellite it shows between 9-13ft accuracy.

 

I walked down the driveway to the end of the road. It still put me next to the road as I walked up and down the street.

 

I do have the unit zoomed in as close as possible and the key in the bottom left shows the 20ft as the measuring distance.

 

I just dont know if I should reset this, or return it or if thats the nature of these?

[+Cacheoholic]

You are expecting too much from your GPS and maps. The best street detail maps you can get are the City Navigator maps and you still will not be on the road 100% of the time. That’s why Garmin made a “lock on roads” option to snap your location to the nearest road. If 20’ accuracy isn’t good enough then you’ll have to wait a couple years for the GPS 2F system to come online and commercial GPSr’s to receive the L5 signal from it.

[yogazoo]

I just dont know if I should reset this, or return it or if thats the nature of these?

 

When your zoomed "all the way in" the road line is only showing you the center line and not the whole road at that zoom level. In real terms, when zoomed in to 20ft, the road line is only about 5 feet wide (2.5 feet on either side of the center line) so if your not driving exactly down the center line you'll always be off the center of the line on your GPS, ALWAYS.

 

Zoom out a bit and stop obsessing. There's alot of potential for errors on the magnitude of what your seeing. If you want or need centimeter accuracy spend $7,000 on a Trimble.

 

[+Walts Hunting]

15 feet is well within most error radius expectations. GPS's are not generally accurate to tht level or smaller. I wouldn't be worried about 15 feet.

 

As to Lock on Road with the 100K's; they are not routable so the GPS doesn't know there is a road there. With a routable map (24K or DN) and lock on road it will lock to it but then when you get out to find the cache you have to turn it off.

[Geo J&Sly]

Thanks for the responses Cacheholic and yogazoo. That is what I needed to hear if thats the case. Like mentioned my biggest worry then is it will not put me on the trail maps I download, when I am driving my dirtbike, potentially alone, in the middle of a state forest, where some roads are illegal to be on with my bike .(I want to stay off the illegal ones if I can help it).

 

Should I be worried about that then?

 

Here is a screenshot of my GPS outside a few miuntes ago:

http://s1002.beta.photobucket.com/user/Snake2715/media/IMAG0908.jpg.html?sort=3&o=0

 

Obviously again if that's the nature then I know I didn't get a faulty one and will move on. It sounds like that is what is being said, but I wanted to post a picture just in case.

 

Its also possible that as mentioned when on a downloaded trail i can use lock on roads to lock me on the trail.

 

Thanks for any confirmation. Sometimes we get used to our smartphones and car GPS systems that probably "lock on roads" by default so we don't realize how accurate or not the GPS and or maps are in reality.

 

*Edit - Thank you Walts Hunting yours came in while I wrote the above response, I didn't read it until now.

 

So that sounds like the deal, when trail riding I will lock and when caching, etc I will unlock.

Edited December 3, 2012 by Geo J&Sly

[+Atlas Cached]

You stated above that you were getting 9-13 ft accuracy with your GPSr. Now, add some small amount of map error correction, say even only 5 ft, for a total possible error of maybe 18 feet at that moment.

 

Now, understanding, as stated above, the line on the map that represents the street you are travelling on is simply the -centerline- of the street. Looking at the scale on the screenshot you supplied, anyone can see the GPSr is positioning you about 15 ft. from the -center- of the street.

 

How far were you really from the -center- of the street?

 

That's as good as it gets for at least the next few years, unless you want to spend several thousand dollars on more accurate equipment.

[Geo J&Sly]

Ok so for cars I will use a vehicle GPS. So the good news is seems I don't have a defective unit. I thought maybe it was positioning me 10-15 feet off and it needed to be reset or similar.

 

I imagine that for the trail it will work if I have pre downloaded maps and lock on, for those rare instances I am blazing my own trail, I guess I will take into account the potential discrepancy when I am checking my route after the fact.

 

Thanks everyone, sounds like given my car and phone GPS "on road" experience I thought I had a potentially faulty unit.

 

In the pic above I was on the center of the road, its a typical 2 lane road.

Edited December 3, 2012 by Snake2715