[HN Gopher] The Universal Transverse Mercator (UTM) geographic c...
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       The Universal Transverse Mercator (UTM) geographic coordinate
       system
        
       Author : brendanashworth
       Score  : 20 points
       Date   : 2025-04-01 20:31 UTC (4 days ago)
        
 (HTM) web link (www.mibsar.com)
 (TXT) w3m dump (www.mibsar.com)
        
       | driggs wrote:
       | 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
        
         | Waterluvian wrote:
         | In undergrad we made a habit of saying and writing "North" or
         | "South" because of this confusion.
         | 
         | (Also: Zone 17T represent!)
        
         | chipsa wrote:
         | 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).
        
       | SiempreViernes wrote:
       | > 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!
        
         | Waterluvian wrote:
         | 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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       (page generated 2025-04-05 23:01 UTC)