.\" Automatically generated by Pod::Man 4.09 (Pod::Simple 3.35)
.\"
.\" Standard preamble:
.\" ========================================================================
.de Sp \" Vertical space (when we can't use .PP)
.if t .sp .5v
.if n .sp
..
.de Vb \" Begin verbatim text
.ft CW
.nf
.ne \\$1
..
.de Ve \" End verbatim text
.ft R
.fi
..
.\" Set up some character translations and predefined strings.  \*(-- will
.\" give an unbreakable dash, \*(PI will give pi, \*(L" will give a left
.\" double quote, and \*(R" will give a right double quote.  \*(C+ will
.\" give a nicer C++.  Capital omega is used to do unbreakable dashes and
.\" therefore won't be available.  \*(C` and \*(C' expand to `' in nroff,
.\" nothing in troff, for use with C<>.
.tr \(*W-
.ds C+ C\v'-.1v'\h'-1p'\s-2+\h'-1p'+\s0\v'.1v'\h'-1p'
.ie n \{\
.    ds -- \(*W-
.    ds PI pi
.    if (\n(.H=4u)&(1m=24u) .ds -- \(*W\h'-12u'\(*W\h'-12u'-\" diablo 10 pitch
.    if (\n(.H=4u)&(1m=20u) .ds -- \(*W\h'-12u'\(*W\h'-8u'-\"  diablo 12 pitch
.    ds L" ""
.    ds R" ""
.    ds C` ""
.    ds C' ""
'br\}
.el\{\
.    ds -- \|\(em\|
.    ds PI \(*p
.    ds L" ``
.    ds R" ''
.    ds C`
.    ds C'
'br\}
.\"
.\" Escape single quotes in literal strings from groff's Unicode transform.
.ie \n(.g .ds Aq \(aq
.el       .ds Aq '
.\"
.\" If the F register is >0, we'll generate index entries on stderr for
.\" titles (.TH), headers (.SH), subsections (.SS), items (.Ip), and index
.\" entries marked with X<> in POD.  Of course, you'll have to process the
.\" output yourself in some meaningful fashion.
.\"
.\" Avoid warning from groff about undefined register 'F'.
.de IX
..
.if !\nF .nr F 0
.if \nF>0 \{\
.    de IX
.    tm Index:\\$1\t\\n%\t"\\$2"
..
.    if !\nF==2 \{\
.        nr % 0
.        nr F 2
.    \}
.\}
.\" ========================================================================
.\"
.IX Title "Geo::HelmertTransform 3pm"
.TH Geo::HelmertTransform 3pm "2018-04-02" "perl v5.26.1" "User Contributed Perl Documentation"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
Geo::HelmertTransform
.SH "VERSION"
.IX Header "VERSION"
1.14
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\&    use Geo::HelmertTransform;
\&
\&    my ($lat, $lon, $h) = ...; # from OS map
\&    my $airy1830 = Geo::HelmertTransform::datum(\*(AqAiry1830\*(Aq);
\&    my $wgs84 = Geo::HelmertTransform::datum(\*(AqWGS84\*(Aq);
\&
\&    ($lat, $lon, $h)
\&        = Geo::HelmertTransform::convert_datum($airy1830, $wgs84,
\&                                                $lat, $lon, $h);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
Perform transformations between geographical coordinates in different datums.
.PP
It is usual to describe geographical points in terms of their polar coordinates
(latitude, longitude and altitude) referenced to a \*(L"datum ellipsoid\*(R", 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.
.PP
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.
.SH "CONVENTIONS"
.IX Header "CONVENTIONS"
Latitude is expressed in degrees, positive-north; longitude in degrees,
positive-east. Heights (ellipsoid) and cartesian coordinates are in meters.
.SH "FUNCTIONS"
.IX Header "FUNCTIONS"
.IP "rad_to_deg \s-1RADIANS\s0" 4
.IX Item "rad_to_deg RADIANS"
Convert \s-1RADIANS\s0 to degrees.
.IP "deg_to_rad \s-1DEGREES\s0" 4
.IX Item "deg_to_rad DEGREES"
Convert \s-1DEGREES\s0 to radians.
.IP "geo_to_xyz \s-1DATUM LAT LON H\s0" 4
.IX Item "geo_to_xyz DATUM LAT LON H"
Return the Cartesian (X, Y, Z) coordinates for the geographical coordinates
(\s-1LAT, LON, H\s0) in the given \s-1DATUM.\s0
.IP "xyz_to_geo \s-1DATUM X Y Z\s0" 4
.IX Item "xyz_to_geo DATUM X Y Z"
Return the geographical (\s-1LAT, LON, H\s0) coordinates for the Cartesian coordinates
(X, Y, Z) in the given \s-1DATUM.\s0 This is an iterative procedure.
.IP "convert_datum D1 D2 \s-1LAT LON H\s0" 4
.IX Item "convert_datum D1 D2 LAT LON H"
Given geographical coordinates (\s-1LAT, LON, H\s0) in datum D1, return the
corresponding coordinates in datum D2. This assumes that the transformations
are small, and always converts via \s-1WGS84.\s0
.IP "datum \s-1NAME\s0" 4
.IX Item "datum NAME"
Return the datum of the given \s-1NAME.\s0 Currently implemented are:
.RS 4
.IP "Airy1830" 4
.IX Item "Airy1830"
The 1830 Airy ellipsoid to which the British Ordnance Survey's National Grid is
referenced.
.IP "Airy1830Modified" 4
.IX Item "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.
.IP "\s-1WGS84\s0" 4
.IX Item "WGS84"
The global datum used for \s-1GPS.\s0
.RE
.RS 4
.RE
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fIA guide to coordinate systems in Great Britain\fR,
http://www.gps.gov.uk/guidecontents.asp
.PP
\&\fIMaking maps compatible with \s-1GPS\s0\fR,
http://www.osni.gov.uk/downloads/Making%20maps%20GPS%20compatible.pdf
.SH "AUTHOR AND COPYRIGHT"
.IX Header "AUTHOR AND COPYRIGHT"
Written by Chris Lightfoot, team@mysociety.org
.PP
Copyright (c) \s-1UK\s0 Citizens Online Democracy.
.PP
This module is free software; you can redistribute it and/or modify it under
the same terms as Perl itself.