Scroll to navigation

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

NAME

Geo::Proj - Handling projections

SYNOPSIS

 use Geo::Proj;
 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);

DESCRIPTION

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 new() 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.

METHODS

Constructors

Geo::Proj-> new([NICK], OPTIONS)
 
Create a new object.
 
 Option--Default
 name    <from proj4>
 nick    <required>
 proj4   <required>
 srid    undef
 
. 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 OBJECT.
 
. 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.

Attributes

$obj-> name
 
The full, official name of the projection
$obj-> nick
 
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.
 
example:
 
 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;
$obj-> srid
 
The "Spatial Reference System ID" if known.

Projecting

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)
Geo::Proj-> dumpProjections([FILEHANDLE])
 
Print details about the defined projections to the FILEHANDLE, which defaults to the selected. Especially useful for debugging.
Geo::Proj-> listProjections
 
Returns a sorted lost of projection nicks.
Geo::Proj-> projection(NICK|PROJ)
 
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.
 
example:
 
 my $wgs84 = Geo::Proj->projection('wgs84');
 my $again = Geo::Proj->projection($wgs84);
$obj-> to([PROJ|NICK], PROJ|NICK, POINT|ARRAY-OF-POINTS)
Geo::Proj-> to([PROJ|NICK], PROJ|NICK, POINT|ARRAY-OF-POINTS)
 
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.
 
example:
 
 my $p2 = $wgs84->to('utm31-wgs84', $p1);
 my $p2 = $wgs84->to($utm, $p1);
 my $p2 = Geo::Proj->to('wgs84', 'utm31-wgs84', $p1);

UTM

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 default projection.
 
example:
 
 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.
 
example:
 
 my $point = Geo::Point->longlat(2.234, 52.12);
 my $proj  = Geo::Proj->bestUTMprojection($point);
 print $proj->nick;    # for instance utm31-wgs84
$obj-> zoneForUTM(POINT)
Geo::Proj-> zoneForUTM(POINT)
 
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.

SEE ALSO

This module is part of Geo-Point distribution version 0.93, built on May 19, 2010. 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 "Geo::Format::Landsat".
Please post questions or ideas to the mailinglist at http://geo-perl@list.hut.fi

LICENSE

Copyrights 2005-2010 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 http://www.perl.com/perl/misc/Artistic.html
2010-05-19 perl v5.14.2