Geocache coordinates

[+SARJ=4V]

Ok, I have had the last cpl people tell me my coords are about 30' or more off. I have a magellan explorist gc and it has a feature "Add geocache" basically you click on this where the geocache is placed and it takes about 40 secs to 1 minute for it to average a waypoint, and then u can save that coord.

 

So this is what I have been doing to get the location coords. I was told that I needed to take more than 1 reading, soI figured ok...I'll go do that and maybe this will give me better coords. I took my explorist wich i have the caches saved into. Each one read 3-6' when i was standing at the cache with the original coord. I walked to the James & Eliza, and the HOG warts cache from 4 different directions, and got the exact same coords each time. I was able to get a slightly diff coord with farmin it up/lagoon (the last number changed by 1) but both coords got me to the location within 3-6'.

 

I was also told that if I felt I had a good coord, to match it up with google maps. Alright so....I figured I would try and see what the location coords I get if I looked at a map, and had the position translated into a gps coord. I used the website http://itouchmap.com/latlong.html

 

I was able to actually get a really good level of zoom. I did both the howells lagoon & evening with the grandparents The coords that I have online for the lagoons are N 41° 43' 07.9788" W 96° 59' 46.0212", When I went to the above mentioned web page and placed the marker on the corner of the building in which the cache is hid, I got the coords. N 41 43 07.4892 W 96 59 46.5102 For EWTG I have online N 41° 43' 41.9988" W 97° 0' 46.0188", doing the same with the web page above i got. N 41 43 41.7642 W97 0 46.3176

 

Any thoughts or help would be appreciated

[+msrubble]

Why are you using degrees, minutes, and seconds? geocaching.com uses degrees decimal minutes.

 

Which datum are you using? geocaching.com uses WGS84.

 

Edited to add: and you should trust your GPS more than online maps.

Edited April 9, 2011 by msrubble

[+Gitchee-Gummee]

Just for argument sake...

 

I would never use online maps to verify my GPSr. Compare the coords, yes, but never as a means of verification. I EXPECT the maps to be off a bit -- not always, but enough to equate them to a "good guess" simply because you just never know....

 

GPSr units will show a bit of differential -- certainly consumer-grade units will. If you wanna be dead-nutz on, go buy one of those that put a cruise missile through a window. Good luck with that one.

[+SARJ=4V]

Why are you using degrees, minutes, and seconds? geocaching.com uses degrees decimal minutes.

 

Which datum are you using? geocaching.com uses WGS84.

 

Edited to add: and you should trust your GPS more than online maps.

 

Ok, well first off I was using DMS because that is what I had my gps set for (when placing a cache or looking up a cache it gives you a choice between several different types.....)would DDM be more accurate On my gps'r i have the choices of DEG/MIN/SEC DEG/MIN.MMM DEG.DDDDD UTM, a bunch of different grids, MGRS, OSGB

 

Yes I have my map datum set to WGS84.

 

I do trust my coordinates but am not sure why they are so off for others.......I did not use the "map" to get my coordinates, I used my GPS'r Just wondering what/ if anything that I should do

[+mpilchfamily]

You need to use Deg Min.MMM. That would be why your cords are off. Deg/min.mmm is more accurate then Deg/min/sec.

[+StarBrand]

You need to use Deg Min.MMM. That would be why your cords are off. Deg/min.mmm is more accurate then Deg/min/sec.

Not to mention not a format easy to type into this website.

[+dfx]

You need to use Deg Min.MMM. That would be why your cords are off. Deg/min.mmm is more accurate then Deg/min/sec.

 

Not if you have and use decimal seconds (i.e. DDD MM' SS.ss''). If you only have one digit after the decimal point in the seconds (SS.s'') then you get about half the precision as with MM.mmm'. That's still only about +- 3 meters in the worst case, good enough for a cache placement. If you don't have any decimals in the seconds, then yeah, rounding is likely to make the coords quite a bit off.

[+edscott]

Just for argument sake...

 

I would never use online maps to verify my GPSr. Compare the coords, yes, but never as a means of verification. I EXPECT the maps to be off a bit -- not always, but enough to equate them to a "good guess" simply because you just never know....

 

GPSr units will show a bit of differential -- certainly consumer-grade units will. If you wanna be dead-nutz on, go buy one of those that put a cruise missile through a window. Good luck with that one.

 

I "Expect " the maps to be off a bit from the cache's actual location also.

[+SARJ=4V]

You need to use Deg Min.MMM. That would be why your cords are off. Deg/min.mmm is more accurate then Deg/min/sec.

 

Ok I will try this and see if it makes it better...thanks for all the info!!!!!!!!!!!

[+Warnerspot]

Okay. I want to thank all the contributors for the information. My wife and I went looking for several and could not find them. I hope the change in format of the coordinates helps. THANKS!

[+LizzyHoops]

Just for argument sake...

 

I would never use online maps to verify my GPSr. Compare the coords, yes, but never as a means of verification. I EXPECT the maps to be off a bit -- not always, but enough to equate them to a "good guess" simply because you just never know....

 

GPSr units will show a bit of differential -- certainly consumer-grade units will. If you wanna be dead-nutz on, go buy one of those that put a cruise missile through a window. Good luck with that one.

 

Ha, As an iphone user I would PERFER the coordinates to match the map, even if that was slightly off. But hey that's me, and not the way the game was invented to be played.

[+SARJ=4V]

You need to use Deg Min.MMM. That would be why your cords are off. Deg/min.mmm is more accurate then Deg/min/sec.

 

Just wanted to let you know, that I went and updated my coords using the DM.mmm. It def. made a difference! The coords were changed and the difference was what otherss had said they were off. Just wanted to thank everyone for their input and this newb really appreciated all the help!

[N4AOF]

You need to use Deg Min.MMM. That would be why your cords are off. Deg/min.mmm is more accurate then Deg/min/sec.

 

Neither display format is inherently more or less accurate than any other display format.

 

Precision and accuracy are not the same thing.

 

The precision of the formats differs somewhat - but the number of decimal places is the controlling factor in precision.

 

As you move from Degrees, to minutes, to seconds, the precision increases by a factor of 60:

 

A coordinate given in whole degrees and minutes (no decimal places) would be 60 times more precise than one given in just whole degrees (yes, both would be useless).

 

A coordinate given in whole degrees, whole minutes, and whole seconds would be 60 times more precise than one given in just whole degrees and whole minutes.

 

Adding decimal places further enhances the precision by a factor of 10 for each decimal place.

 

Thus a coordinate given as DDD/MM.m would be less precise than one given as DDD/MM/SS, but a coordinate given as DDD/MM.mm would be slightly more precise than one given as DDD/MM/SS

 

Precision is useless without accuracy -- the distinction between precision and accuracy is often forgotten in this digital age where it is easy to display figures that are far more precise than the accuracy of the actual measurement. If you have a bathroom scale with an accuracy of +/- 1% there is really no good reason to pay attention to the fact that it displays your weight to a precision of 2/10th of a pound.

 

As for his coordinates "being off" because he gave them in DDD/MM/SS.sss it is far more likely that the error arose when someone tried to convert those numbers for entry into a GPS configured for DDD/MM.mmmm

[+StarBrand]

You need to use Deg Min.MMM. That would be why your cords are off. Deg/min.mmm is more accurate then Deg/min/sec.

 

Not if you have and use decimal seconds (i.e. DDD MM' SS.ss''). If you only have one digit after the decimal point in the seconds (SS.s'') then you get about half the precision as with MM.mmm'. That's still only about +- 3 meters in the worst case, good enough for a cache placement. If you don't have any decimals in the seconds, then yeah, rounding is likely to make the coords quite a bit off.

Totally irrelevant as either's precision is well inside of the Unit's general accuracy.

[+dfx]

Totally irrelevant as either's precision is well inside of the Unit's general accuracy.

 

Not irrelevant if the curious newby reads this, misinterprets the given information and starts to believe that coordinates given in deg/min/sec are inaccurate and will put the location off. Because that is exactly what the post that I replied to implied.

[GeoJava]

Regardless of format, I've learned that no matter what you use to get the coords, one set of averages does not necessarily get you to GZ, especially in heavy cover. I now take the approach of 3 sets of averages triangulating equidistant around the cache. I then post them to Google Earth and get the coords in the middle.

[+Gitchee-Gummee]

Regardless of format, I've learned that no matter what you use to get the coords, one set of averages does not necessarily get you to GZ, especially in heavy cover. I now take the approach of 3 sets of averages triangulating equidistant around the cache. I then post them to Google Earth and get the coords in the middle.

 

Uuhhhhh......... While I know that you are trying to be as accurate as possible, what you are describing (at least the way you state it), is that you are using MAPS to obtain the coordinates. I'm not trying to be nit-picky, but it seems you are putting a lot of faith in the map, or map program, when few others do.

 

I have used Google Earth, entering coordinates supplied by various sources. Sometimes they are dead-on, other times Google Earth shows me something up to or over a mile away!

 

You just never know, for sure. I think that is why the guidelines state:

Listings must contain accurate GPS coordinates. You must visit the geocache site and obtain all the coordinates with a GPS device. GPS usage is an integral and essential element of both hiding and finding geocaches and must be demonstrated for all cache submissions.

 

Besides that, most other geocachers will be using a GPSr to find the placement. They have to deal with the canopy/cover as do you!