The Universal Transverse Mercator (UTM) geographic coordinate system | Hacker News Reader

The Universal Transverse Mercator (UTM) geographic coordinate system

mibsar.com

This page actually points out a minor frustration that I frequently experience with UTM in GIS software and GPS receivers, under the "MGRS grid row designators".

These MGRS row designators are completely optional and redundant, because a UTM northing values span the entire Y dimension of a Zone.

What is not redundant is the hemisphere designator, "N" or "S".

There are 20 row designators, and the designers excluded the letters "I" and "O" to avoid confusion with the visibly-similar numbers "1" and "0". There are 26 letters in the alphabet to choose from, but they did not bother to exclude the letters "N" or "S".

It just so happens that the row which covers half of the continental United States - which is in the Northern hemisphere - is the row labeled "S".

So well-meaning GIS software and even Garmin GPS receivers often call my zone "17S", which reads as "Zone 17, Southern Hemisphere". My zone is in fact "17N", "Zone 17, Northern Hemisphere". This is especially annoying given that the row label is an artifact of MGRS and not civilian UTM.

http://www.mibsar.com/LandNav/UTM/UTM.htm#Rows

In undergrad we made a habit of saying and writing “North” or “South” because of this confusion.

(Also: Zone 17T represent!)

You are in MGRS zone 17S. MGRS also has grid square designations after the zone, and before the easting/northing numbers. A full UTM coordinate string will only have N/S at position 2/3, while a full MGRS coordinate string will have 3 characters at that position. A MGRS string will also be 2 characters shorter than an equivalent UTM string.

Civilian UTM doesn’t handle things near the poles very well. MGRS explicitly uses the zone characters to change to a polar projection. Those other 4 characters not used for row identification actually identify polar areas (NE, NW, SE, SE semi-hemispheres).

> Every UTM grid is perfectly square and exactly the same size. All UTM coordinate grids are perfectly square and exactly the same size — 1,000 meters by 1,000 meters — across the entire grid system.

Since the Earth does in fact not have a circumference that's a integer multiple of 1 km, does this mean this projection just leaves out some sliver of the Earth's surface?

East to west its not too bad, just 17 metres off, but north to south that's over 800 meter of extra surface to hide!

Holes are left at the poles. A filler is the Universal Polar Stereographic projection.

UTM actually doesn’t cover a lot more than you think. Because at the extreme poles exaggeration would make them basically useless.I think they terminate at 84 degrees N and 80 degrees S.

It’s been a long time since I studied this stuff so I’d look this all up rather than take my word.

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