Geo::Proj - Handling projections
my $wgs84 = Geo::Proj->new # predefined if import()
( nick => 'wgs84'
, proj4 => '+proj=latlong +datum=WGS84 +ellps=WGS84'
my $clrk = Geo::Proj->new
( nick => 'clark66'
, proj4 => [proj => "merc", ellps => "clrk66", lon_0 => -96]
my $point_wgs84= Geo::Point->latlong(56.12, 4.40, 'wgs84');
my $point_wgs84= Geo::Point->latlong(56.12, 4.40, $wgs84);
my $point_clrk = $point_wgs84->in($clrk);
my $point_clrk = Geo::Proj->to($wgs84, $clrk, $point_wgs84);
my $point_clrk = Geo::Proj->to($wgs84, 'clark66', $point_wgs84);
A point on Earth's surface can be represented in many different coordinate
systems. The Geo::Proj4 module wraps the popular Open Source
"libproj" library to convert between those coordinate systems; a
very complex job.
Within a program, however, you like some extra abstraction from that library: to
be able to simply label a point to its system, and then forget about all
transformations which may be necessary. The label (or "nick") hides
all complicated parameters for the actual projection .
WARNING 1: this class will collect all nicks, which means that calling
with the same label twice will have the second ignored.
WARNING 2: the wgs84 nickname is predefined, but only if this module is 'used'
with import. So if you decide to use 'require' to dynamically load this
module, then don't forget to call ' import()
' yourself, or define the
wgs84 projection yourself.
- Geo::Proj->new([$nick], %options)
- Create a new object.
name <from proj4>
- name => STRING
- nick => LABEL
- The abbrevated name for this projection.
- proj4 => OBJECT|ARRAY|STRING
- The ARRAY or STRING will by used to create a Geo::Proj4 object by calling
Geo::Proj4::new(). You may also specify such an prepared
- srid => INTEGER
- SRID stands for "Spatial Reference System ID", which is just an
index in a table of spatial descriptions as used by SQL. Only INTEGER
values larger than 0 are permitted.
- The full, official name of the projection
- Simple abbreviating of the projection.
- $obj->proj4([ <$nick|$proj4> ])
- Geo::Proj->proj4([ <$nick|$proj4> ])
- Returns the projection library handle (a Geo::Proj4) to be used by this
component. As class method, the $nick is specified for a lookup. In case a
$proj4 is specified, that is returned.
my $wgs84 = Geo::Proj->new(nick => 'wgs84', ...);
my $wgs84_proj4 = Geo::Proj->proj4('wgs84');
my $wgs84_proj4 = Geo::Proj->proj4($wgs84);
my $wgs84_proj4 = $wgs84->proj4;
- The "Spatial Reference System ID" if known.
- Geo::Proj->defaultProjection([ <$nick|$proj> ])
- The $nick must be defined with new(). Returned is the Geo::Proj
object for the default projection. The default is the first name created,
which probably is 'wgs84' (when import() had a chance)
- Print details about the defined projections to the $fh, which defaults to
the selected. Especially useful for debugging.
- Returns a sorted lost of projection nicks.
- Returns the Geo::Proj object, defined with $nick. In case such an object
is passed in as $proj, it is returned unaffected. This method is used
where in other methods NICKS or $proj can be used as arguments.
my $wgs84 = Geo::Proj->projection('wgs84');
my $again = Geo::Proj->projection($wgs84);
- $obj->to([<$proj|$nick>], <$proj|$nick>,
- Geo::Proj->to([<$proj|$nick>], <$proj|$nick>,
- Expects an Geo::Proj to project the $point or $points to. The work is done
by Geo::Proj4::transform(). As class method, you have to specify
two nicks or projections.
Be warned that this to() method expects POINTs which are not
Geo::Point objects, but which themselves are an ARRAY containing X,Y and
optionally a Z coordinate.
my $p2 = $wgs84->to('utm31-wgs84', $p1);
my $p2 = $wgs84->to($utm, $p1);
my $p2 = Geo::Proj->to('wgs84', 'utm31-wgs84', $p1);
- Geo::Proj->UTMprojection(<$datum|$proj|undef>, $zone)
- The $proj is a Geo::Proj which is used to collect the datum information
from if no $datum was specified explicitly. It may also be a string which
is the name of a datum, as known by proj4. Undef will be replaced by the
my $proj = Geo::Proj->UTMprojection('WGS84', 31) or die;
print $proj->nick; # for instance utm31-wgs84
- $obj->bestUTMprojection($point, [$proj|$nick])
- Geo::Proj->bestUTMprojection($point, [$proj|$nick])
- Returns the best UTM projection for some $point. As class method, you
specify the nickname or the object for the point.
my $point = Geo::Point->longlat(2.234, 52.12);
my $proj = Geo::Proj->bestUTMprojection($point);
print $proj->nick; # for instance utm31-wgs84
- Provided some point, figure-out which zone is most optimal for
representing the point. In LIST context, zone number, zone letter, and
meridian are returned as separate scalars. In LIST context, the zone
number and letter are returned as one..
This code is stolen from Geo::Coordinates::UTM, because that module
immediately starts to do computations with this knowledge, which is not
wanted here. Probably a lot of zones are missing.
- overload: '""' (stringification)
- Returns the nick-name for this projection.
This module is part of Geo-Point distribution version 0.96, built on January 21,
2014. Website: http://perl.overmeer.net/geo/
All modules in this suite:
"Geo::Point", "Geo::Proj4", "Geo::WKT",
"Math::Polygon", "Geo::GML", "Geo::ISO19139",
"Geo::EOP", "Geo::Format::Envisat", and
Please post questions or ideas to the mailinglist at
Copyrights 2005-2014 by [Mark Overmeer]. For other contributors see ChangeLog.
This program is free software; you can redistribute it and/or modify it under
the same terms as Perl itself. See