UTM codes

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The cache web pages I have looked at show the UTM zone and coordinates as something like:

UTM: 10S E 559831 N 4157226

or

UTM: 18T E 741100 N 4591620

or

UTM: 54H E 291891 N 6100730

At first I thought the "S" was an error and should be an "N" for zone 10 North, but then I saw one in CT (zone 18 North) and IA (zone 15 North) with "T"s and one in Australia with "H". What do the letters "S", "T", and "H" refer to? Why not "N" and "S" for North and South?

I didn't see this in the FAQ.

This should do it...

UTM GRID ZONES

I believe the Letter on the zone specifies a subset of a zone, but it is not really needed.

UTM: 10S E 559831 N 4157226

is the same as

UTM: 10 559831E 4157226N

My USGS map of my assigned quadrangle in Missouri say "15" and not "15S".

DustyJacket

...If life was fair, a banana split would cure cancer.

You are correct. The numbers represent vertical zones, while the letters represent horizontal zones. So, if you wanted to tell me your approximate location (like where you live) you could tell me you live in zone 15S, and it would give me an idea where you're at, even without the coords. Telling me you lived in zone 15 would be much more vague.

That being said, I don't believe the letter is necessary when stating coords, as the numbers used are distances from the equator and prime meridian. So, it's not possible (in my understanding) to have two sets of identical coords, only differenciated by the zone designation.

Greg

N 39 54.705'

W 77 33.137'

quote:
Originally posted by gnbrotz:

That being said, I don't believe the letter is necessary when stating coords, as the numbers used are distances from the equator and prime meridian. So, it's not possible (in my understanding) to have two sets of identical coords, only differenciated by the zone designation.

Close. The measurement is from the equator and the central meridian of the zone, so it is possible to have the same coordinates in two different numeric zones, but you're right that the letters don't matter. Also, there's a "false northing" and a "false easting" added to the numbers, so they aren't just distances.

There is no false northing value in the northern hemisphere, a false easting value of 500,000 meters is given to the central meridian of each zone.

USGS (http://mac.usgs.gov/mac/isb/pubs/factsheets/fs07701.html) doesn't use the UTM military grid (http://www.tpub.com/inteng/9h.htm) so that's why their maps don't have the military latitude codes (and why I hadn't heard of it).

If the letters are N and S for north and south, the original N and S that I refered to, then they do matter. The other system of military grid letters are extra and confusing. Does "10S" refer to 10 South or military grid 10S, where the latter is really UTM zone 10 North? Here on geocaching.com, I now know UTM designations are are military grid designations.

quote:
Originally posted by Warm Fuzzies - Fuzzy:

Close. The measurement is from the equator and the central meridian of the zone, so it is possible to have the same coordinates in two different numeric zones, but you're right that the letters don't matter. Also, there's a "false northing" and a "false easting" added to the numbers, so they aren't just distances.

Thanks for straightening me out Fuzzy. My friend who originally taught me about UTM and sold me on it, doesn't visit these forums. He and I had a discussion about the possibility of duplicate coords a while back, and he convinced me of what I stated above. Now I guess it's time for me to do a little teaching.

Greg

N 39 54.705'

W 77 33.137'

[This message was edited by gnbrotz on March 05, 2003 at 10:26 AM.]

quote:
Originally posted by brad.32:

If the letters are N and S for north and south, the original N and S that I refered to, then they do matter. The other system of military grid letters are extra and confusing. Does "10S" refer to 10 South or military grid 10S, where the latter is really UTM zone 10 North? Here on geocaching.com, I now know UTM designations are are military grid designations.

The UTM coordinates on the cache pages are not MGRS (military grid reference system) which is an extension of the UTM coordinate system. There are sixty UTM zone numbers in 6 degree longitudinal strips extending from 80 degrees south latitude to 84 degrees north latitude. The UTM zone characters are letters which designate 8 degree zones extending north and south from the equator. Beginning at 80 degrees south and proceeding northward, twenty bands are lettered C through X, omitting I and O. MGRS adds two more letters that designate 100km squares.