My GPS way points don't match up.

[+The Ocotillo 8]

I have a Delorme PN-20, my first Gps unit, I got it to Geocach, etc. On my first hide/placing of a cach I marked the way point, I moved away and double checked the location with the GPS. When I got back home I logged on and entered our cach location, and other info. The next weekend we went out to the cach, and

it Geocach.com numbers were different then mine (I knew this, but thought the differents was a few feet.the differents was 20 yards, across the road. It seems the web site rounds off the last 2 numbers of my location, and that makes the differents... I want to place 2 more caches this coming weekend, but don't want to have to go back out and relocate them after the web site rounds them off. I guess my question is what am I doing wrong???? Thanks

[+root1657]

I have a Delorme PN-20, my first Gps unit, I got it to Geocach, etc. On my first hide/placing of a cach I marked the way point, I moved away and double checked the location with the GPS. When I got back home I logged on and entered our cach location, and other info. The next weekend we went out to the cach, and

it Geocach.com numbers were different then mine (I knew this, but thought the differents was a few feet.the differents was 20 yards, across the road. It seems the web site rounds off the last 2 numbers of my location, and that makes the differents... I want to place 2 more caches this coming weekend, but don't want to have to go back out and relocate them after the web site rounds them off. I guess my question is what am I doing wrong???? Thanks

 

I think this is going to be an easy fix for you.

 

The thing is, there are as many ways to measure the planet as people who have ever found a need to measure it. Each time someone makes a new way to do it, the number systems are enevitably different. Some of them are deceptively similar.... your unit and the web site arent rounding off digits, they are using different ways of measuring the planet. All you need to do is to set your unit to display coords in the same format that geocaching uses and you should be back in business. Mine unit shows it is set to use WGS 84, so try that and see if it doesnt fix your problem. It has another setting for display format, which on mine is set to hddd mm.mmm, but if you have extra digits, then it is probably set incorrectly to some other way of measuring, or another way of displaying the location.

 

I work with a civil engineer who gets seriously bent anytime someone brings this up, because he wishes everyone could just settle on one standard and let the others die.

 

Happy hunting (and hiding)!

[+Ed56]

I agree with the entry above. It is very important to make sure your Gps receiver is set to use the WGS 84 Datum and not, for example. NAD27 or some other datum. Go to your unit's setup menu then to its' navigation page and you should be able to make sure you are using WGS 84. Also set your units to read in degrees, minutes and decimal minutes. For example N32 45.210

Something to keep in mind is that none of this navigation business is exact. Regardless of which brand of unit you have, all consumer grade GPS receivers will display errors to varying degrees. They simply are not designed to be extremely precise/accurate. (You may find it interesting to look up the difference in these 2 terms). Let your unit sit and average its' readings for several minutes before marking your waypoint. Also pay attention to the EPE (expected positional error) displayed on your screen. Typically you may get slightly better accuracy in the morning or at night when the atmosphere is less ionized by the sun's radiation. You may be getting multi-path signals if you are in an area with a lot of buildings and heavy vegetation can interfere with GPS signals too. Be patient and check your reading several times before submitting them. Good luck!

Edited March 24, 2008 by Ed56

[+GeePierceS]

if there's trees overhead, after I've marked a waypoint, I like to tell my GPS to 'goto' that waypoint, walk a 100 feet or so away where its clear overhead, and walk directly towards the waypoint, see if the GPS indicated direction and distance agrees. then do this from a few different angles, if they all triangulate on your marked waypoint, its probably correct, otherwise, adjust it.

 

if your GPS supports WAAS, this can get you a much more accurate reading, at the expense of slower updates, and more battery consumption. my little geko gets within 10' with clear skies overhead.

 

at typical USA mid latitudes, 0.020 arcminutes difference is something like 100 feet give or take, and 0.001 minute, which is as accurate as most GPS's readout, is like 5 feet. without WAAS, my GPS gives 20-30 feet accuracy under the best of conditions and in light woods maybe only 80-100 feet accuracy and repeatability.

[+The Ocotillo 8]

I want to thank everyone that responded to my question. My unit was set to NAD27 instead of WGS84. I guess that was the problem, I’ll check it out this coming weekend when we go back out the desert area where the cache is. When I set the org. waypoint my unit set it at N 32deg 43.0750’ W116deg 04.0776”, It got changed to N32deg 43.071’ W116deg 04.776 when posted. When I set the original waypoint I went back twice to add items, and the GPS took me right to the cache with almost no error (+ - 3ft.) Anyway I think I’m on the same page as the web site now. Thanks again to all that answered so quickly.. Jim

[+Renegade Knight]

I want to thank everyone that responded to my question. My unit was set to NAD27 instead of WGS84. I guess that was the problem, I’ll check it out this coming weekend when we go back out the desert area where the cache is. When I set the org. waypoint my unit set it at N 32deg 43.0750’ W116deg 04.0776”, It got changed to N32deg 43.071’ W116deg 04.776 when posted. When I set the original waypoint I went back twice to add items, and the GPS took me right to the cache with almost no error (+ - 3ft.) Anyway I think I’m on the same page as the web site now. Thanks again to all that answered so quickly.. Jim

 

You have an easy fix. Tell your GPS to be on WGS 84. It should update the waypoint automaticly and all should be good. You can plug that revised waypoint into the site and it should work correctly. Another visit to the desert just to fix this problem isn't needed.

[+The Ocotillo 8]

I want to thank everyone that responded to my question. My unit was set to NAD27 instead of WGS84. I guess that was the problem, I’ll check it out this coming weekend when we go back out the desert area where the cache is. When I set the org. waypoint my unit set it at N 32deg 43.0750’ W116deg 04.0776”, It got changed to N32deg 43.071’ W116deg 04.776 when posted. When I set the original waypoint I went back twice to add items, and the GPS took me right to the cache with almost no error (+ - 3ft.) Anyway I think I’m on the same page as the web site now. Thanks again to all that answered so quickly.. Jim

 

You have an easy fix. Tell your GPS to be on WGS 84. It should update the waypoint automaticly and all should be good. You can plug that revised waypoint into the site and it should work correctly. Another visit to the desert just to fix this problem isn't needed.

 

Thanks, but I need to move the cache back to where I want it insead of where the Cache page has it, and then fix the waypoint on the site. Beside we live in the desert half of the time, got a place in Ocotillo,CA 92259 Jim