Calibrating your GPS?

[IngramFamily]

Hi

 

We are newbies and are having trouble with the accuracy of our GPS. We bought a Etrex which we realise is a basic one however that was all we wanted to spend. Found a couple of caches in the weekend however the GPS said we were still 500m away from destination. We hid our first cache in the weekend and I see that pumkinguy has placed a log saying he could not find it!!!! Help!!

[+WRASTRO]

If you were 500m away I don't even think having the wrong datum set up on your GPS could cause that large of an error. I would suggest finding an experienced cacher local to you to meet up with and compare settings.

 

Welcome to the game and be patient with this. I am sure there is a logical explanation for your challenge.

[IngramFamily]

If you were 500m away I don't even think having the wrong datum set up on your GPS could cause that large of an error. I would suggest finding an experienced cacher local to you to meet up with and compare settings.

 

Welcome to the game and be patient with this. I am sure there is a logical explanation for your challenge.

 

 

Hi

 

I have just checked our location (according to our address we entered) on this website and compared it to what the GPS tells us. Below are the results. Would this variance equal 500m?

Geocaching.com

S 37 043'488

E 174 56'919

 

GPS

S 37 043'298

E 174 56'558

[+Lovejoy and Tinker]

If you were 500m away I don't even think having the wrong datum set up on your GPS could cause that large of an error. I would suggest finding an experienced cacher local to you to meet up with and compare settings.

 

Welcome to the game and be patient with this. I am sure there is a logical explanation for your challenge.

 

 

Hi

 

I have just checked our location (according to our address we entered) on this website and compared it to what the GPS tells us. Below are the results. Would this variance equal 500m?

Geocaching.com

S 37 043'488

E 174 56'919

 

GPS

S 37 043'298

E 174 56'558

 

The difference between those coordinates is 0.635 km, or 635 meters.

 

Don't know if that helps or not. Nor do I know why your GPS should be reading incorrectly. But I know a website that does the sums

 

How on earth have you managed to find any caches with that degree of variance

Edited October 26, 2010 by Lovejoy and Tinker

[+Huntleigh]

Hi

 

We are newbies and are having trouble with the accuracy of our GPS. We bought a Etrex which we realise is a basic one however that was all we wanted to spend. Found a couple of caches in the weekend however the GPS said we were still 500m away from destination. We hid our first cache in the weekend and I see that pumkinguy has placed a log saying he could not find it!!!! Help!!

 

Hi I see you're Kiwis. As others have suggested you might need some help from some local geocachers.

 

The NZ section on this forum is not frequented that much and you would have better luck on the GPS.org.nz forum.

 

Better still, go to an Event cache and learn from the veterans. There's one coming up in Auckland in a week or two, The Wonders of Spring #3

Edited October 26, 2010 by Huntleigh

[+Stargazer22]

You might be having a problem with the coordinate format and the datum you are set for on your unit.

 

Coordinate formats on the geocaching website are in DDD MM.MMM format. You should set your unit to the same format. The datum setup should be set to WGS84.

 

On any geocache page, next to the coordinates, there is a link for "other conversions". You can look there to see if other coordinate conversions look like what you see on your receiver. That will tell you that you are indeed set for other settings instead of the defaults you will see on the coordinates on the website.

 

Most units have an option in the setup menu to change the coordinate format and datum. Check your owner's manual for setting details.

 

Good luck!

[+Gitchee-Gummee]

My guess is what Stargazer22 says.

 

They way that that you typed the coords in your posting do not seem correct. Perhaps it is simply the way that you typed them, but it can be confusing to beginners using a GPSr.

 

Your device must be set on WGS84, using a DECIMAL format (you had typed it as minutes/seconds) -- that may be your problem.

 

Most all units are easily switchable through the main menu, eTrex included.

 

Good Luck.

[+dfx]

coordinate format would be my guess too.

 

if the numbers you see look like 12.34567, then that's decimal degrees. sometimes you have a degree symbol after that and the hemisphere before or after it: N 12.34567°

 

if it looks like 12 34.567, then that's degrees and decimal minutes. the complete format is N 12° 34.567' (the apostrophe means minutes)

 

the third common format is minutes and seconds: 12 34 56.7 or N 12° 34' 56.7'' (the double apostrophe means seconds)

 

all those refer to different locations. make sure you use the same format on the GPSr as whatever you're comparing the coordinates with.

 

i believe your GPSr is set to display minutes+seconds, while geocaching.com always uses decimal minutes.

 

Geocaching.com S 37 043'488 E 174 56'919

GPS S 37 043'298 E 174 56'558

if my assumption is right, then the coords from gc.com are really S 37° 43.488' E 174° 56.919', while the coords from the GPS are really S 37° 43' 29.8'' E 174° 56' 55.8''. converting the seconds from the GPSr to minutes, you get S 37° 43.497' E 174° 56.930', which is much closer to what you get from gc.com.

Edited October 26, 2010 by dfx

[Todd_196]

I have the same unit and I too am new to the hobby. And I too was off a bit. The reason....I got button happy! try re-seting your unit to all defaults. There is an option on one of the screens. From there the only additional thing I did was turn the WAAS on.

 

After that give it another shot!

 

Good luck and Cach on!

[+John in Valley Forge]

When I first started, I was very dubious of the readings on my GPSr. So I took it to several places that I could pinpoint on Google Maps. For me it was flagpoles in front of local buildings. They stood out on the satellite images. I compared the readings I got at those locations on the GPSr to the coordinates shown on Google maps and after a few of them was able to figure out what I was doing wrong. Looking at just one didnt help, I needed to to a few before I caught on. For the life of me I don't remember what my error was though.

[+Huntleigh]

Hi

 

We are newbies and are having trouble with the accuracy of our GPS. We bought a Etrex which we realise is a basic one however that was all we wanted to spend. Found a couple of caches in the weekend however the GPS said we were still 500m away from destination. We hid our first cache in the weekend and I see that pumkinguy has placed a log saying he could not find it!!!! Help!!

 

Hi I see you're Kiwis. As others have suggested you might need some help from some local geocachers.

 

The NZ section on this forum is not frequented that much and you would have better luck on the GPS.org.nz forum.

 

Better still, go to an Event cache and learn from the veterans. There's one coming up in Auckland in a week or two, The Wonders of Spring #3

 

Oh and another thing, if you want to "calibrate" your GPS (you can really only check it against a known point) there is a benchmark cache on Mt Eden. It is a surveyed mark accurate to 0.0000001 of a minute while your unit is probably reporting 0.001.

[mtbikernate]

If you were 500m away I don't even think having the wrong datum set up on your GPS could cause that large of an error. I would suggest finding an experienced cacher local to you to meet up with and compare settings.

 

Welcome to the game and be patient with this. I am sure there is a logical explanation for your challenge.

 

 

Hi

 

I have just checked our location (according to our address we entered) on this website and compared it to what the GPS tells us. Below are the results. Would this variance equal 500m?

Geocaching.com

S 37 043'488

E 174 56'919

 

GPS

S 37 043'298

E 174 56'558

 

I agree you need to check your coordinate format, but I am curious about the comment I bolded. Did you possibly enter a street address and get a set of coordinates returned? If that's the case, keep in mind that the coordinates of an address are not known precisely.

 

My house, for example, is listed by Google Maps/Earth in the wrong place entirely. Google thinks my street ends before it ever gets to my backyard. The street my driveway enters has a different name entirely. If I measure the straightline distance between my ACTUAL driveway as seen on the sat imagery and the point where Google THINKS my address is (someone else's backyard), I see that it's already 150m off. And my driveway is 18.5m long.

 

Add that to any error introduced by using the wrong format, and you'll be in trouble every time.

 

I suggest reading up on coordinate formats enough that you can recognize them and distinguish between them. Once you get that squared away, your GPS should get you within 10m of a given point very easily and sometimes within 2-5m given good environmental conditions.

[IngramFamily]

Hi

Thank you for that . Have changed the format to ddd'mm.mmm and our coordinates for our home are a lot closer. Also changed to WSG84.

Regards

Julie

 

 

 

 

 

You might be having a problem with the coordinate format and the datum you are set for on your unit.

 

Coordinate formats on the geocaching website are in DDD MM.MMM format. You should set your unit to the same format. The datum setup should be set to WGS84.

 

On any geocache page, next to the coordinates, there is a link for "other conversions". You can look there to see if other coordinate conversions look like what you see on your receiver. That will tell you that you are indeed set for other settings instead of the defaults you will see on the coordinates on the website.

 

Most units have an option in the setup menu to change the coordinate format and datum. Check your owner's manual for setting details.

 

Good luck!

[IngramFamily]

Hi

 

Thank you for all the helpful advice. By changing the format to ddd mm.mmm our current location gives the following co ordinates;

 

GPS

S 37 04.497 (have not figures out how to get to degrees symbol)

E 174 56.934

 

geocaching.com

(by going find my location)

S 37 04.488

E 174 56.919

 

What is this variance? Is it now close enough?

 

We have only ever found caches off the clues once we are in the general area.

 

Regards

Julie

[+dfx]

GPS

S 37 04.497 (have not figures out how to get to degrees symbol)

E 174 56.934

 

geocaching.com

(by going find my location)

S 37 04.488

E 174 56.919

 

What is this variance? Is it now close enough?

that's 27.7 meters. not quite "spot on", but pretty good for a geocoded location.

 

but this would be a good chance to actually test out your GPS properly. look at the map on gc.com and see where exactly the marker is pointing to. then create a waypoint on your GPS at those coordinates (the ones from gc.com) and then tell it to navigate to that waypoint. it will tell you the distance to the waypoint and you can use it to get closer to it. see where you end up.

Edited October 28, 2010 by dfx

[+Huntleigh]

Hi

 

Thank you for all the helpful advice. By changing the format to ddd mm.mmm our current location gives the following co ordinates;

 

GPS

S 37 04.497 (have not figures out how to get to degrees symbol)

E 174 56.934

 

geocaching.com

(by going find my location)

S 37 04.488

E 174 56.919

 

What is this variance? Is it now close enough?

 

We have only ever found caches off the clues once we are in the general area.

 

Regards

Julie

 

Hi Julie

 

When you are doing these comparisons you always have to remember there are two sources of error. There is the error of your GPS and then the error of your 'benchmark". I presume to get your "benchmark" you entered your address into the "find my location"? But remember your address is not a point but an area. What part of your property is "find my location" using to give your location? The front boundary? The centre? The back fence?

 

I don't believe you can be confident about the position reported by 'find my location'. I would still recomend a quick blast up the motorway to the Benchmark cache on Mt Eden. (The actual benchmark is to the east of the trig station and is set set in the ground).

 

The Benchmark will give you absolute certainty on your position, and you get another cache your total to boot. There is also an Earthcache on the summit Mountain of Eden so you'll get two for the price of one!

 

Happy hunting

Edited October 28, 2010 by Huntleigh