=encoding utf8

=head1 NAME

Geo::Proj - Handling projections

=head1 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);

=head1 DESCRIPTION

A point on Earth's surface can be represented in many different coordinate
systems.  The L<Geo::Proj4|Geo::Proj4> module wraps the popular Open Source C<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
C<nick>) hides all complicated parameters for the actual projection .

WARNING 1: this class will collect all nicks, which means that calling
L<new()|Geo::Proj/"Constructors"> 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.

=head1 METHODS

=head2 Constructors

=over 4

=item Geo::Proj-E<gt>B<new>( [$nick], %options )

Create a new object.

 -Option--Default
  name    <from proj4>
  nick    <required>
  proj4   <required>
  srid    undef

=over 2

=item name => STRING

=item nick => LABEL

The abbrevated name for this projection.

=item proj4 => OBJECT|ARRAY|STRING

The ARRAY or STRING will by used to create a L<Geo::Proj4|Geo::Proj4> object
by calling L<Geo::Proj4::new()|Geo::Proj4/"Instantiation">.  You may also specify such an
prepared OBJECT.

=item 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.

=back

=back

=head2 Attributes

=over 4

=item $obj-E<gt>B<name>()

The full, official name of the projection

=item $obj-E<gt>B<nick>()

Simple abbreviating of the projection.

=item $obj-E<gt>B<proj4>( [ <$nick|$proj4> ] )

=item Geo::Proj-E<gt>B<proj4>( [ <$nick|$proj4> ] )

Returns the projection library handle (a L<Geo::Proj4|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;

=item $obj-E<gt>B<srid>()

The "Spatial Reference System ID" if known.

=back

=head2 Projecting

=over 4

=item Geo::Proj-E<gt>B<defaultProjection>( [ <$nick|$proj> ] )

The $nick must be defined with L<new()|Geo::Proj/"Constructors">.  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)

=item Geo::Proj-E<gt>B<dumpProjections>( [$fh] )

Print details about the defined projections to the $fh, which
defaults to the selected.  Especially useful for debugging.

=item Geo::Proj-E<gt>B<listProjections>()

Returns a sorted lost of projection nicks.

=item Geo::Proj-E<gt>B<projection>( <$nick|$proj> )

Returns the L<Geo::Proj|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);

=item $obj-E<gt>B<to>( [<$proj|$nick>], <$proj|$nick>, $point|ARRAY-of-$points )

=item Geo::Proj-E<gt>B<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 L<Geo::Proj4::transform()|Geo::Proj4/"Converters">.  As class method, you have to
specify two nicks or projections.

Be warned that this L<to()|Geo::Proj/"Projecting"> method expects POINTs which are
B<not> L<Geo::Point|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);

=back

=head2 UTM

=over 4

=item Geo::Proj-E<gt>B<UTMprojection>( <$datum|$proj|undef>, $zone )

The $proj is a L<Geo::Proj|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

=item $obj-E<gt>B<bestUTMprojection>( $point, [$proj|$nick] )

=item Geo::Proj-E<gt>B<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

=item $obj-E<gt>B<zoneForUTM>($point)

=item Geo::Proj-E<gt>B<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 L<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.

=back

=head1 OVERLOADING

=over 4

=item overload: B<'""' (stringification)>

Returns the nick-name for this projection.

=back

=head1 SEE ALSO

This module is part of Geo-Point distribution version 0.98,
built on February 01, 2019. Website: F<http://perl.overmeer.net/CPAN/>

=head1 LICENSE

Copyrights 2005-2019 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 F<http://dev.perl.org/licenses/>