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Converting Utm To Wgs84

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Change the datum on your GPS to the same datum that the UTM's are in, enter the coords. then you can change back to WGS84 and they should change. And are you sure the UTM Coords are not it WGS84 I have a lot of people that search for my caches presume that the Datum is 27 because Delorme is 27. While I use 84 just like the main page of the cache description and put it on Nat Geo TOPO.


I just looked up a set of coordinates on a Nat Geo's Trails illustrated and the coords change when you change the datum.

Zone 13 T

  • Nad 27 460969mE 4486046mN
  • WGS84 460924mE 4486256mN

And even those these numbers are different the place is the same, Trail Junction at Donner Pass.

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First off, I will point out that your question is somewhat mis-stated (even though we understand what you meant). UTM is a coordinate system (expressed as coordinates). WGS84 is a Datum (a mathematical model representating the shape of the Earth).


There are lots of Coordinate Systems (Lat/Long being a quite popular alternative to UTM). Remember, there are many more.


There are many Datums (NAD27 is a popular alternative to WGS84). Again these are just two examples of many available.


Tahosa is correct that you can use your GPSr to convert to and from any combination of Coordinate Sysyems and Datums. But let's just list the possibilities for the examples I discussed above.


1. UTM in WGS84 to UTM in NAD27

2. UTM in WGS84 to LAT/LONG in WGS84

3. UTM in WGS84 to LAT/LONG in NAD27

4. Any of those 3 examples back to UTM in WGS84

5. LAT/LONG in WGS84 to LAT/LONG in NAD27 and back again if necessary.


And all those different ways of representing this information, all point to exactly the same location. And during all this conversion, nothing actually changes inside the GPSr. The only thing that changes is the way the information is displayed on the GPSr screen.


There is a program named GeoCalc that was written by a fellow Geocacher (fizzymagic) and made available for our use. Thanks Fizzy! It can be downloaded to your computer, and be run offline. It will do Coordinate Conversion (in the WGS84 Datum), but not Datum Conversion. The interface is quite intelligent. Just experiment with it.


Here is an interesting (milti Datum) Lat/Lon, UTM, Magnetic Declination Calculator that you can download (Free) and run offline. It does all calculations in real time (You don't have to hit a Calculate Button). Change 1 digit and everything updates.


Geographic Magnetic Calculator

Edited by Cardinal Red
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