Military Grid Reference System: Difference between revisions

Revision as of 22:53, 11 February 2022

Revision as of 22:27, 11 March 2022

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One always reads map coordinates from west to east first (easting), then from south to north (northing). Common mnemonics include "in the house, up the stairs", "left-to-right, bottom-to-top" and "Read Right Up".

===TruncateTruncation, don'tnot roundrounding===

As mentioned above, when converting UTM coordinates to an MGRS grid reference, or when abbreviating an MGRS grid reference to lower precision, one should ''{em|truncate''}} the coordinates, not round. This has been controversial in the past, since the oldest specification, TM8358.1,<ref name="DMA8358_1_Chapter3"/> used rounding, as did GEOTRANS<ref name="Geotrans">[http://earth-info.nga.mil/GandG/geotrans/index.html GEOTRANS] Geographic Translator software and source code from the US National Geospatial-Intelligence Agency.</ref> before version 3.0.

However, truncation is used in GEOTRANS since version 3.0, and in NGA Military Map Reading 201<ref name="Military_Map_Reading_201"/> (page 5) and in the US Army Field Manual 3-25.26.<ref name="Field_Manual_3_25_26">[http://www.globalsecurity.org/military/library/policy/army/fm/3-25-26/index.html Map Reading and Land Navigation], U.S. Army Field Manual No. 3-25.26 (see section 4-6).</ref> The civilian version of MGRS, [[USNG]], also uses truncation.<ref name="Cavell">J. Anthony Cavell, [http://www.amerisurv.com/PDF/TheAmericanSurveyor_USNationalGrid-Cavell_June2005.pdf USNG: Getting it right the first time]. ''The American Surveyor,'' June 2005.</ref>