Verify coord readings on gps

[widgit]

I am new at using my E-trex (yellow) gps. I have two questions:

 

1) How do I determine if my gps unit is providing accurate readings. If the pgs unit is inaccurate how do I correct it?

 

2) Any suggestions on how to get closer to the cache when the gps reading is always off?

I read about how people get better coords when placing a cache. Same process to find a cache?

 

Whenever I search for a cache I have found that I am off by at least 20-40 degrees. I realize that may not seem like much, but when I am still learning what to look for ...just finding the general area in a park or the right yard on a street means a whole lot.

[+admo1972]

One thing I did (which was quite fun) was to take a reading while on the deck of my house and note the coordinates. Then move 20 or 30 feet and take another reading. Then hop onto maps.google.com, switch to satellite view and paste the coordinates in. Google pointed me almost spot-on.

 

This only works, however, if google has relatively hi-rez images of your location.

[+Robespierre]

Every time you change batteries your gps needs to be calibrated. It sounds like maybe you need to do that. Then check which style of coordinates you are set for: N40 41.062 is the correct style. There is a FAQ to explain this, and your etrex booklet should also.

[+sbell111]

I am new at using my E-trex (yellow) gps. ...

 

Whenever I search for a cache I have found that I am off by at least 20-40 degrees. ...

I'm confused. Are you talking about the unit's electronic compass?

 

The good news is that the little yellow etrex (the basic one that retails for about $99, not the kinda orange venture cx) doesn't have an internal compass). It's arrow doesn't (necessarily) point towards ground zero unless you are walking.

Edited April 27, 2007 by sbell111

[+sbell111]

I am new at using my E-trex (yellow) gps. I have two questions:

 

1) How do I determine if my gps unit is providing accurate readings. If the pgs unit is inaccurate how do I correct it?

 

2) Any suggestions on how to get closer to the cache when the gps reading is always off?

I read about how people get better coords when placing a cache. Same process to find a cache?

 

Whenever I search for a cache I have found that I am off by at least 20-40 degrees. I realize that may not seem like much, but when I am still learning what to look for ...just finding the general area in a park or the right yard on a street means a whole lot.

It's actually pretty unlikely that your GPSr is giving results that are any worse than anybody else's. You might want to go to the next event in your area and compare the coords that you are getting with other people's. If you unit is actually giving you significantly different readings, contact Garmin. Their service is really good.

 

I suspect that the real problem is that you are completely relying on the GPSr to take you to the cache. Most of the time, the best you will do is get in the general area of the cache. Once your GPSr says that you are there, put it away and look around you. Think about the best places to hide a cache within twenty feet or so of where you are.

[+sbell111]

Every time you change batteries your gps needs to be calibrated. It sounds like maybe you need to do that. Then check which style of coordinates you are set for: N40 41.062 is the correct style. There is a FAQ to explain this, and your etrex booklet should also.

Since the little yellow etrex doesn't have an electronic compass, it doesn't need to be calibrated. Edited April 27, 2007 by sbell111

[widgit]

Thanks for your comments! Widgit

[+Y2KOTA]

I sent a e-mail to Garmin about the how accurate are the readings on my Garmin GPS III, Here's the meat of the reply I got back......

 

"I would suggest you walk or drive a familier path to check the accuracy.

There is no technical procedure to follow. "

 

I'm still new at this, what else can I add, if that's what I got from Garmin!!!

 

Oh, I know, it was suggested to me to check the "Datum" setting. Some else should be able to help with that part.

[nonaeroterraqueous]

Whenever I search for a cache I have found that I am off by at least 20-40 degrees. I realize that may not seem like much, but when I am still learning what to look for ...just finding the general area in a park or the right yard on a street means a whole lot.

When I first saw this I thought you were talking about degrees longitude or latitude. Oh, yes, that does seem like much. Now, I'm not sure what you mean.

 

One thing I did recently to check GPS accuracy was to find a nearby benchmark with an adjusted location (not scaled). I entered the posted coordinates into the receiver and set it to "GOTO." Then I placed it directly on top of the benchmark and got a difference of a little over three feet. That was the eTrex Yellow. My Legend C got a difference of a foot.

[+fehrgo]

One thing I did (which was quite fun) was to take a reading while on the deck of my house and note the coordinates. Then move 20 or 30 feet and take another reading. Then hop onto maps.google.com, switch to satellite view and paste the coordinates in. Google pointed me almost spot-on.

hi-rez images of your location.

 

Keep in mind that the images on Google maps are approximately layered onto the earth, and in some places such as parts of Calgary are off by 150 meters (or more). As a result, you may think it is your GPSr that is off, when in fact your GPSr is fine. Some users mention getting coordinates for their caches from google earth, which makes me shudder.

[+minxyy]

our Gpsr shows use wading through the sea at some caches! But we didn't just the land isn't counted when you get to the sea shore!

 

We've had issues with being 10 ft out if it's got to 100ft out and the day is clear I've e-mailed the cache owners with my reading so they can build up a picture of 'positions' if others have sent them in, which may enable them to do more averaging.......this has received both positive and negative feedback (but there's always those who's machine is the best/most accurate and they won't budge).

 

I don't use the compas on my GPSr I bought a 'proper' one for a few quid which is much easier to use.

 

Have fun and good luck caching .......don't forget to pack your geocachers nose! (in our case it's usually 'princessannie who's got it whilst everyone else is following the yellow box round in circles! I've started to switch the gpsr off when we are within 10ft of a cache now as we are more observent without it!)

 

Have a great weekend

minxyy

[+fehrgo]

Another potential issue is multipath - if I approach within 15m of a large metal structure such as a roof or bridge, my reading will suddenly shoot off 15-20m to the left as I approach the coordinates. This is likely due to the re-radiation of the GPS signal from the structure, confusing the chipset in the GPSr. This has been a problem on at least two caches that I can remember. The GPSr in question is a Magellan Explorist 500.

[+Trucker Lee]

One way to get around problems with structures, trees, or even the variance of the unit when you get too close to GZ is to see where the arrow points from several locations. For example, from 50 feet out, see where the GPSr points you, move sideways and look again, and once more if you want.

[widgit]

Regarding the accuracy of my gps:

 

Oops, meant feet instead of degrees. Sorry 'bout that.

 

These additional ideas and suggestions will keep me busy while I get know my gps.

 

Thank you sooo much.

 

This is great info for all tadpoles...members, too.

[+Markwell]

If you're in doubt about the accuracy of your GPS, find a local benchmark that has a high control accuracy rating and see what happens when you try to find it.

 

Be sure to go back on a different day and see the different results.

 

That will also give you an idea of how wide of a search area you might need for your caches.

[+dzrt1st]

You also have to take into account the GPSr used to set the cache coords. You may think your GPSr is off but it may be the one used by the placer of the cache that is off.

 

FWIW

Todd