Talk:Universal Transverse Mercator coordinate system

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[edit] Graphics are still needed

This page still needs graphics showing the following:

  • The 60 UTM zones overlain on a map of the world
  • The process by which points are measured (eastings and northings)
  • Perhaps a diagram showing how a 6° wide UTM zone wraps around the globe like a strip of paper

I will see if I can aquire any of these from other publications.

Justin 03:16, 23 August 2005 (UTC)

I've added a graphic that may satisfy the first two requirements. mdf 16:43, 29 October 2005 (UTC)
Very nice graphic, thanks! If you wouldn't mind moving a bit of the information in the image's description into the article (particularly about the discrepencies, and why they exist), that would be great. I'd do it myself, but my knowledge about the topic is only cursory, and I'm afraid I'd get something wrong. Phidauex 17:00, 29 October 2005 (UTC)
I've re-arranged things a bit, added the technicalities, and linked to the MGRS. I also marked the MGRS article as a stub. I'll see if I can make some graphics for that one.
As for UTM's exceptions: I have no idea why they exist. Two possibilites I can think of (1) for the convenience of the Norwegian people (but then, why not for the people of Edmonton?), or (2) perhaps those areas were important, or felt to become important, immediately after WWII, and the problems of converging meridians would have been a operational mess. mdf 20:10, 29 October 2005 (UTC).
On the European map, the Norwegian exception is shown slightly wrong. The boundary line between 31V and 32V should follow longitude 3°E (the middle of zone 31), but the European map shows the boundary too far east, around 4.5°E. The world map is correct, though. --Mikael R 08:58, 20 February 2007 (UTC)

[edit] A couple of tables?

first table two collums long(range)-UTM 0-60
second table LAt(range)-UTM A-Z
or is it the otheray around 
I'll but this on my to do later list :)

--Mkouklis 12:06, 16 September 2006 (UTC)

[edit] Notation?

In the entry, it says: "This is in longitude zone 17, and the grid position is 630084m east, 4833438m north." How do you notate.

There isn't really a standard notation, but there are conventions. The easting should be given before the northing. This would likely be most common way to write out that position:
630084 mE 4833438 mN zone 17
However, since the easting is usually given first, and the easting always has one less digit than the northing, that position could be given as: 6300844833438 zone 17. That particular style of notation isn't used very frequently anymore. - Justin 23:12, 25 October 2006 (UTC)
Note that you would also want to include which zone 17 (eg, 17T 630084E 4833438N). Some notations add an initial zero to easting to give it the same number of digits as northing. Also, some GPS receivers I have used switch the order and give Northing/Easting, but the general convention seems to be easting first.Shouriki 00:22, 5 May 2007 (UTC)

[edit] UTM is not a map projection

UTM is not map projection. The Universal Transverse Mercator coordinate system consists of 60 zones, each of which is defined by a unique point of origin, false easting, and Transverse Mercator projection centered over a specific central meridian with a scale factor of 0.9996 The UTM coordinate system (which is the subject of this article) is a system by which locations can be specified on the globe. It uses map projections. It uses 60 specifically defined Transverse Mercator projections (60 out of an infinite number of possible Transverse Mercator projections) but it itself is not a map projection. - Justin 23:50, 27 October 2006 (UTC)

[edit] Bad see also link

There's a bad link to MTM (Modified Transverse Mercator), which I cannot find anywhere. 70.66.184.59 01:53, 25 January 2007 (UTC)

[edit] Trapezoidal?

Am I to understand that each lettered zone is conceived of as a perfect trapezoid, or are the east and west edges curved?--Homunq 21:41, 26 June 2007 (UTC)

That is like asking whether the equator is curved or straight: it depends on what projection the map is drawn in. In a regular cylindrical projection, like Miller or ordinary Mercator, each grid zone (like 33U) appears as a perfect rectangle. However, suppose a grid zone is drawn in the UTM projection that belongs to its own zone. Then the east and west edge appear slightly curved and convex; the edge that faces the equator usually appears more curved and convex (unless it coincides with the equator: then it appears straight); the edge that faces the nearest pole also appears curved, but concave. For example, the boundary between 33U and 34U is a meridian that appears slightly curved like this ")" when drawn in UTM projection of zone 33, but appears curved the other way, "(", when drawn in UTM projection of zone 34. --Mikael R 17:47, 4 December 2007 (UTC)

[edit] "UTM latitude zone"

I think this is in error. The latitude zones are not part of UTM as defined in DMATM 8358.2. They are part of the Military grid reference system defined in DMATM 8358.1, which is based on UTM. --David Garfield 01:19, 27 July 2007 (UTC)

You are right in theory, I think. In pure UTM notation, one would specify the hemisphere (North or South) instead of the latitude band. But using UTM zone + latitude band letter + UTM coordinates has become a quite common notation: it might be called a de facto standard. Therefore, it is no longer a good idea to use "N" and "S" to stand for north or south hemisphere, since they can be mistaken for latitude band letters. One could write "North" and "South" instead (if everyone knows enough English). Since at least one character is needed to distinguish the North and South hemisphere, why not accept the latitude band letter for this purpose? Some extra redundancy should be a good thing, since some errors might be caught. --Mikael R 17:56, 4 December 2007 (UTC)

[edit] Overlap of zones

I tried it allready in the first part of the article, but my english is not god enough to correct this in the article itself, so let me explain here: As I understand it, it is not correct, that...

"Distortion of scale increases in each UTM zone as the boundaries between the longitude zones are approached."

The distortion increases with the *metric* distance to the central meridian, thats why the west to east width of the UTM-Zones is limited to 800 km, btw. exactly 800 km, and that not because of the distortion but due to the concept that all eastings should have *6 digits*. That leads to the smallest valid easting of 100.000, and 900.000 as the biggest for symetry reasons (100 + 400 = 500 (central meridian) + 400 = 900km). The Zones overlap widely.

Btw. because of that, the "Norway-execption" isn't a real (systematic) eception: At these latitudes even the even zones overlap each other, witch means, in the north there are *no* places, than can only be mapped to one UTM-Zone

may be http://upload.wikimedia.org/wikipedia/commons/thumb/a/a0/Utmzylinderrp.jpg/180px-Utmzylinderrp.jpg helps to understand?

87.160.209.176 22:52, 13 October 2007 (UTC) http://de.wikipedia.org/wiki/Benutzer:Mikl

Yes and no! It is almost true that the distortion depends on the metric distance to the central meridian. I say almost, because the latitude has a tiny effect, caused by the Earth being ellipsoid-shaped rather than spherical. However, the UTM *zones*, as the word is normally used, are *not* 800 km wide with overlap; they are 6 degrees wide (except for the Norway exceptions) and do not overlap. But a UTM *projection* can, as Mikl says, sometimes be used outside its own zone. I know of one official reason (that is, allowed by US military practice) and one non-official reason (national needs in non-Norwegian countries).

Officially: As I remember the documentation, official US military use of UTM is to print topographic paper maps in the scale 1:50000. Of course, it would be awkward if such a map had to stop exactly at a zone boundary, so the map is allowed to continue 20 km (or was it 40 km?) into the next zone, and in the overlap, grid lines for both projections may be shown (in different colors). This makes it possible to measure distances on the map across the zone boundary. But when reporting the position of a point on the map, the coordinates must be expressed in the correct projection, namely for the zone that contains the point.

Non-officially: Finland, for example, uses the UTM projection for zone 35 for country-wide mapping, even though Finland is wider than zone 35. Is the resulting coordinate reference system an instance of UTM? No. It must be renamed in some way, to indicate the non-standard width. The coordinate system is therefore called ETRS-TM35FIN, where FIN signals that this is a national modification. If we wrote just ETRS-TM35, it would mean UTM used strictly within zone 35. (The ETRS stands for the common European geodetic datum, which coincides with WGS84 except for about half a meter. I think ETRS-UTM35 would have been a better name, but perhaps you cannot say "Universal" when you use a geodetic datum that only is defined in Europe.) See http://www.kolumbus.fi/eino.uikkanen/geodocsgb/ficoords.htm for more details.

Sweden does the same thing with UTM zone 33. It would have been nice if the resulting coordinate reference system had been called ETRS-TM33SWE, but it is not. It is called SWEREF99 TM (which is not the same as the older Swedish Grid). 28 Oct 2007, http://en.wikipedia.org/wiki/User:Mikael_R —Preceding unsigned comment added by 81.231.148.193 (talk) 21:53, 28 October 2007 (UTC)

[edit] Idiots' caveat addition

Speaking as an idiot, I came to some grief as a consequence of ignorance over map projections and specifically UTM. Popular schoolboy impression of Mercator is a projection of the globe onto a cylinder. It isn't, it's carefully rescaled for conformality. The issue of conformality isn't very visible -0 you can Google UTM and search hard to find out a precise definition, and I thought it would be helpful to highlight that, so that anyone else contemplating coding up UTM would at least refer to e.g. Snyder. Please amend/delete if you disagree. —Preceding unsigned comment added by Monopodia (talk • contribs) 14:49, 28 December 2007 (UTC)Monopodia (talk) 14:58, 28 December 2007 (UTC)Andy Smith