Geo::HelmertTransform(3pm)				User Contributed Perl Documentation				Geo::HelmertTransform(3pm)

NAME

       Geo::HelmertTransform

VERSION

       1.14

SYNOPSIS

	   use Geo::HelmertTransform;

	   my ($lat, $lon, $h) = ...; # from OS map
	   my $airy1830 = Geo::HelmertTransform::datum('Airy1830');
	   my $wgs84 = Geo::HelmertTransform::datum('WGS84');

	   ($lat, $lon, $h)
	       = Geo::HelmertTransform::convert_datum($airy1830, $wgs84,
						       $lat, $lon, $h);

DESCRIPTION

       Perform transformations between geographical coordinates in different datums.

       It is usual to describe geographical points in terms of their polar coordinates (latitude, longitude and altitude) referenced to a "datum
       ellipsoid", which is used to approximate the Earth's geoid. The latitude, longitude and altitude of a given physical point vary depending
       on which datum ellipsoid is in use.  Unfortunately, a number of ellipsoids are in everyday use, and so it is often necessary to transform
       geographical coordinates between different datum ellipsoids.

       Two different datum ellipsoids may differ in the locations of their centers, or in their shape; and there may be an angle between their
       equatorial planes or the meridians relative to which longitude is measured. The Helmert Transform, which this module implements, is a
       linear transformation of coordinates between pairs of datum ellipsoids in the limit of small angles of deviation between them.

CONVENTIONS

       Latitude is expressed in degrees, positive-north; longitude in degrees, positive-east. Heights (ellipsoid) and cartesian coordinates are in
       meters.

FUNCTIONS

       rad_to_deg RADIANS
	   Convert RADIANS to degrees.

       deg_to_rad DEGREES
	   Convert DEGREES to radians.

       geo_to_xyz DATUM LAT LON H
	   Return the Cartesian (X, Y, Z) coordinates for the geographical coordinates (LAT, LON, H) in the given DATUM.

       xyz_to_geo DATUM X Y Z
	   Return the geographical (LAT, LON, H) coordinates for the Cartesian coordinates (X, Y, Z) in the given DATUM. This is an iterative
	   procedure.

       convert_datum D1 D2 LAT LON H
	   Given geographical coordinates (LAT, LON, H) in datum D1, return the corresponding coordinates in datum D2. This assumes that the
	   transformations are small, and always converts via WGS84.

       datum NAME
	   Return the datum of the given NAME. Currently implemented are:

	   Airy1830
	       The 1830 Airy ellipsoid to which the British Ordnance Survey's National Grid is referenced.

	   Airy1830Modified
	       The modified 1830 Airy ellipsoid to which the Irish Grid (as used by Ordnance Survey Ireland and Ordnance Survey Northern Ireland);
	       also known as the Ireland 1975 datum.

	   WGS84
	       The global datum used for GPS.

SEE ALSO

       A guide to coordinate systems in Great Britain, http://www.gps.gov.uk/guidecontents.asp

       Making maps compatible with GPS, http://www.osni.gov.uk/downloads/Making%20maps%20GPS%20compatible.pdf

AUTHOR AND COPYRIGHT

       Written by Chris Lightfoot, team@mysociety.org

       Copyright (c) UK Citizens Online Democracy.

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

perl v5.12.4							    2011-08-29						Geo::HelmertTransform(3pm)