
NAME
       Geo::Coordinates::UTM - Perl extension for Latitiude Lon­
       gitude conversions.

SYNOPSIS
       use Geo::Coordinates::UTM;

       ($zone,$easting,$northing)=latlon_to_utm($ellipsoid,$lati­
       tude,$longitude);

       ($latitude,$longitude)=utm_to_latlon($ellip­
       soid,$zone,$easting,$northing);

DESCRIPTION
       This module will translate latitude longitude coordinates
       to Universal Transverse Mercator(UTM) coordinates and vice
       versa.

       Mercator Projection

       The Mercator projection was first invented to help
       mariners. They needed to be able to take a course and know
       the distance traveled, and draw a line on the map which
       showed the day's journey. In order to do this, Mercator
       invented a projection which preserved length, by project­
       ing the earth's surface onto a cylinder, sharing the same
       axis as the earth itself.  This caused all Latitude and
       Longitude lines to intersect at a 90 degree angle, thereby
       negating the problem that longitude lines get closer
       together at the poles.

       Transverse Mercator Projection

       A Transverse Mercator projection takes the cylinder and
       turns it on its side. Now the cylinder's axis passes
       through the equator, and it can be rotated to line up with
       the area of interest. Many countries use Transverse Merca­
       tor for their grid systems.

       Universal Transverse Mercator

       The Universal Transverse Mercator(UTM) system sets up a
       universal world wide system for mapping. The Transverse
       Mercator projection is used, with the cylinder in 60 posi­
       tions. This creates 60 zones around the world.  Positions
       are measured using Eastings and Northings, measured in
       meters, instead of Latitude and Longitude. Eastings start
       at 500,000 on the centre line of each zone.  In the North­
       ern Hemisphere, Northings are zero at the equator and
       increase northward. In the Southern Hemisphere, Northings
       start at 10 million at the equator, and decrease south­
       ward. You must know which hemisphere and zone you are in
       to interpret your location globally.  Distortion of scale,
       distance, direction and area increase away from the cen­
       tral meridian.

       UTM projection is used to define horizontal positions
       world-wide by dividing the surface of the Earth into 6
       degree zones, each mapped by the Transverse Mercator pro­
       jection with a central meridian in the center of the zone.
       UTM zone numbers designate 6 degree longitudinal strips
       extending from 80 degrees South latitude to 84 degrees
       North latitude. UTM zone characters designate 8 degree
       zones extending north and south from the equator. Eastings
       are measured from the central meridian (with a 500 km
      false easting to insure positive coordinates). Northings
       are measured from the equator (with a 10,000 km false nor­
       thing for positions south of the equator).

       UTM is applied separately to the Northern and Southern
       Hemisphere, thus within a single UTM zone, a single X / Y
       pair of values will occur in both the Northern and South­
       ern Hemisphere.  To eliminate this confusion, and to speed
       location of points, a UTM zone is sometimes subdivided
       into 20 zones of Latitude. These grids can be further sub­
       divided into 100,000 meter grid squares with double-letter
       designations. This subdivision by Latitude and further
       division into grid squares is generally referred to as the
       Military Grid Reference System (MGRS).  The unit of mea­
       surement of UTM is always meters and the zones are num­
       bered from 1 to 60 eastward, beginning at the 180th merid­
       ian.  The scale distortion in a north-south direction par­
       allel to the central meridian (CM) is constant However,
       the scale distortion increases either direction away from
       the CM. To equalize the distortion of the map across the
       UTM zone, a scale factor of 0.9996 is applied to all dis­
       tance measurements within the zone. The distortion at the
       zone boundary, 3 degrees away from the CM is approximately
   1%.

       Datums and Ellipsoids

       Unlike local surveys, which treat the Earth as a plane,
       the precise determination of the latitude and longitude of
       points over a broad area must take into account the actual
       shape of the Earth. To achieve the precision necessary for
       accurate location, the Earth cannot be assumed to be a
       sphere. Rather, the Earth's shape more closely approxi­
       mates an ellipsoid (oblate spheroid): flattened at the
       poles and bulging at the Equator. Thus the Earth's shape,
       when cut through its polar axis, approximates an ellipse.
       A "Datum" is a standard representation of shape and offset
       for coordinates, which includes an ellipsoid and an ori­
       gin. You must consider the Datum when working with geospa­
       tial data, since data with two different Datum will not
       line up. The difference can be as much as a kilometer!

EXAMPLES
       A description of the available ellipsoids and sample usage
       of the conversion routines follows
       Ellipsoids

       The Ellipsoids available are numbered as follows:

       1 Airy
       2 Australian National
       3 Bessel 1841
       4 Bessel 1841 (Nambia)
       5 Clarke 1866
       6 Clarke 1880
       7 Everest
       8 Fischer 1960 (Mercury)
       9 Fischer 1968
       10 GRS 1967
       11 GRS 1980
       12 Helmert 1906
       13 Hough
       14 International
       15 Krassovsky
       16 Modified Airy
       17 Modified Everest
       18 Modified Fischer 1960
       19 South American 1969
       20 WGS 60
       21 WGS 66
       22 WGS-72
       23 WGS-84

       latlon_to_utm

       Latitude values in the southern hemisphere should be sup­
       plied as negative values (e.g. 30 deg South will be -30).
       Similarly Longitude values West of the meridian should
       also be supplied as negative values. Both latitude and
       longitude should not be entered as deg,min,sec but as
       their decimal equivalent, e.g. 30 deg 12 min 22.432 sec
       should be entered as 30.2062311

       The ellipsoid value should correspond to one of the num­
       bers above, e.g. to use WGS-84, the ellipsoid value should
       be 23

       For latitude  57deg 49min 59.000sec North
           longitude 02deg 47min 20.226sec West

       using Clarke 1866 (Ellipsoid 5)

            ($zone,$east,$north)=latlon_to_utm(5,57.803055556,-2.788951667)

       returns

            $zone  = 30V
            $east  = 512533.364651484
            $north = 6409932.13416127

       utm_to_latlon

       Reversing the above example,

            ($latitude,$longitude)=utm_to_latlon(5,30V,512533.364651484,6409932.13416127)

       returns

            $latitude  = 57.8330555601433
            $longitude = -2.788951666974

            which equates to
            latitude  57deg 49min 59.000sec North
            longitude 02deg 47min 20.226sec West

AUTHOR
       Graham Crookham, grahamc@cpan.org

COPYRIGHT
       Copyright (c) 2000,2002 by Graham Crookham.  All rights
       reserved.

       This package is free software; you can redistribute it
       and/or modify it under the same terms as Perl itself.


