Talk:Military Grid Reference System
|WikiProject Maps||(Rated C-class, High-importance)|
This needs to be categorized.
Anyone heard of Georef? When I was in the Royal Observer Corps, many years ago, I remember we used "UTM" on some maps, which seems to be the Military grid reference system; co-ordinates (within Europe, say) were like "PQ 123 456". But on other maps, we used a system I remember being called "Georef". This had a similar notation — two letters to identify a major "square", then two or more digits to identify a point within the "square" — but was based on lat-long, not UTM; hence, the "squares" were curved-trapezoids. You got the accuracy of lat-long with the convenient notation of UTM / British grid. Now I can't find any info on Georef (which, if it really existed, sureley deserves a mention). Anyone ever heard of this? — Johantheghost 18:10, 2 December 2005 (UTC)
- OK, to reply to myself, I found some info, and we now have an article on Georef. — Johan the Ghost seance 11:21, 17 February 2006 (UTC)
Such an MGRS coordinate, standing alone, may be converted to latitude and longitude. But you still do not know the position on the Earth, unless you also know the geodetic datum that is used.
Sorry about being too brief, but I hoped people would follow the link to geodetic datum. Actually, a better link would be A guide to coordinate systems in Great Britain, published by the Ordnance Survey. It gives the best explanation of geodetic datums that I have ever seen. Figure 1 in the introduction gives an example of what I meant. --Mikael R (talk) 19:14, 13 May 2008 (UTC)
- I too am confused about why a different coordinate system cannot indicate the same location. Seems to me (an ignorant layman) that it would depend instead on whether they use the same datum. Or is there a rule that says that's not allowed? Jim.henderson (talk) 01:56, 18 January 2011 (UTC)
I don't see how the statement is relevant to MGRS. Yes it's true that lat/lon requires a datum in order to be properly interpreted, but this article is about MGRS, not lat/lon. The rest of the article is focused on MGRS-specific traits, but this sentence about lat/lon is an entry to a whole other set of topics, and I think it's distracting here. It's like it's there just to lead you off into datums and geodesy, etc. Pardon my snarky example, but it would be like me saying that you can enter an MGRS coordinate into a handheld GPS unit, but the GPS won't work without batteries. i.e., not relevant to MGRS. -- LVB (talk) 17:09, 28 June 2013 (UTC)
point reference system
I see no link to "point reference system" nor article by that name. Is the concept explained in another article, or should the distinction between that and other systems be explained in this one? Jim.henderson (talk) 09:29, 16 January 2011 (UTC)
What is a SQ_ID?
- It means Square ID. Also, sign your posts in future using "~~~~", so that we know who we're talking to. – Nohomers48 (talk • contribs) 20:51, 1 September 2013 (UTC)
Sentences on clipping and labeling are confusing
From the article:
- Related to this is the primacy of the southwest corner of the polygon being the labeling point for an entire polygon. In instances where the polygon is not a square and has been clipped by a grid zone junction, the polygon keeps the label of the southwest corner as if it had not been clipped.
I've been researching MGRS for a few days, but the above is totally opaque to me. Does this have something to do with the fact that locations that border GZJs are canonicalized by some software libraries (e.g. 17SKT --> 16SGB5807198790)? We should clarify the above with an example. Ericbg05 (talk) 13:39, 10 June 2014 (UTC)
- It's talking about how some squares like 18N SF don't have a 0,0, easting,northing as the southwest corner is outside of the zone. It's because of UTM. The squares are square in reference to the equator, and the vertical "central meridian" line in the centre of each zone. In UTM, that line is 500,000 easting. 0 easting doesn't exist, it's in the zone to the west. So in MGRS/USNG, the squares on the edges of zones are clipped, but the squares on the west side still use the soutwest corner for 0,0 easting,northing, even though that's a possibly invalid point. I might try to clear up the article, but I want to do more work with USNG/MGRS first to ensure my understanding is correct. Mtfurlan (talk) 16:32, 27 October 2016 (UTC)
Also referred to as "NATO UTM"
This book also references it, but I'm not buying the book to look at the books reference.
I'm not going to edit the actual article without a better reference than a google books link to a book whose sources I can't check.