LL to UTM for Rio Christ - incorrect zone letter? about geodesy HOT 3 CLOSED

Thanks for looking at this issue. http://earth-info.nga.mil/GandG/coordsys/grids/utm.html has a good visualization (below pictures are taken from there) ...

... and this warning:

CAUTION: IN MANY SYSTEMS, THE LETTER AFTER THE ZONE NUMBER DESIGNATES A LATITUDINAL BAND, NOT A HEMISPHERE.

And what you print out is the hemisphere (and not a latitude band).

from geodesy.

There is sometimes confusion beween the UTM coordinate system, and MGRS grid references which are based on UTM.

They are both based on 60 longitudinal zones each 6° wide (zone 23 in your example).

In UTM, a hemisphere designator (N/S) is used, hence the 23 S. Northings in the southern hemisphere are measured from 80°S (7460687 in your example: almost 7,500km).

Whereas MGRS is divided into 20 latitude bands (K in your example) and the 23K ‘GZD’ is divided into 100km squares (PQ in your case: this is shown on the Earth Point site for the ‘MGRS’ calculation).

So it makes no sense for Earth Point to mention the ‘K’ latitude band for the UTM calculation, when the northing (7460686mN) is referenced from 80°S (‘S’ designator) rather than within the K band. It is sad to see a site like that propagating such confusion.

It is explained in greater deatail at www.movable-type.co.uk/scripts/latlong-utm-mgrs.html, which shows both the UTM coordinate and the MGRS grid reference.

from geodesy.

This document (march 2007) http://earth-info.nga.mil/GandG/coordsys/images/utm_mgrs_images/utm_basics_20070319.doc stated out:

THE LETTER AFTER THE UTM ZONE NUMBER: IS THAT A HEMISPHERE OR A LATITUDINAL BAND?

Since the creation of UTM, developers have interpreted the rules for expressing an earth-wide unique UTM position in one of two ways:

1. By including an “N” or “S” after the zone number to specify a hemisphere.
2. By including the 8° latitudinal band designator (see the section on MGRS) after the zone number.

Example: The position at 92°W, 38°N, expressed in UTM coordinates, is:

587798m E, 4206287m N, Zone 15.

This reference is valid for two positions on the earth. In order to make it unique for only one position worldwide, i.e. 92°W, 38°N:

• Developer #1 includes an “N” to specify northern hemisphere:

15N 587798 4206287

• Developer #2 includes the 8° latitudinal band designator:

15S 587798 4206287

This situation is causing confusion among users and developers. The two 8° latitudinal bands, from 0° to 8°N and from 32°N to 40°N, are assigned the designations “N” and “S”, respectively. These designations are often mistaken for hemisphere designations.

Technical Manual 8358.1 contains the authoritative definition of UTM. NGA will soon publish an updated version of TM 8358.1, which will provide clarification on this issue.

from geodesy.