=head1 NAME

Geo::GML - Geography Markup Language processing

=head1 INHERITANCE

 Geo::GML has extra code in
   Geo::GML::GeoPoint

 Geo::GML
   is a XML::Compile::Cache
   is a XML::Compile::Schema
   is a XML::Compile

=head1 SYNOPSIS

 use Geo::GML ':gml321';

 my $gml = Geo::GML->new('READER', version => '3.2.1');

 # see XML::Compile::Cache on how to use readers and writers
 my $data = $gml->reader("gml:GridCoverage")->($xmlmsg);
 my $xml  = $gml->writer($sometype)->($doc, $perldata);

 # or without help of the cache, XML::Compile::Schema
 my $r    = $gml->compile(READER => $sometype);
 my $data = $r->($xml);

 # overview (large) on all defined elements
 $gml->printIndex;

 # To discover the perl datastructures to be passed
 print $gml->template("gml:Surface");

 # autoloaded logic to convert Geo::Point into GML
 $data->{...somewhere...} = $gml->GPtoGML($objects);

=head1 DESCRIPTION

Provides access to the GML definitions specified in XML.  The details
about GML structures can differ, and therefore you should be explicit
which versions you understand and produce.

If you need the <b>most recent</b> version of GML, then you get involved
with the ISO19139 standard.  See CPAN module Geo::ISO19139.

The first releases of this module will not powerful, but hopefully
people contribute.  For instance, an example conversion script between
various versions is very welcome!  It would be nice to help each other.
I will clean-up the implementation, to make it publishable, but do not
have the knowledge about what is needed.

=head1 METHODS

=head2 Constructors

Geo::GML-E<gt>B<new>('READER'|'WRITER'|'RW', OPTIONS)

=over 4

 Option            --Defined in     --Default
 allow_undeclared                     <true>
 any_element         XML::Compile::Cache  ATTEMPT
 hook                XML::Compile::Schema  undef
 hooks               XML::Compile::Schema  []
 ignore_unused_tags  XML::Compile::Schema  <false>
 key_rewrite         XML::Compile::Schema  []
 opts_readers        XML::Compile::Cache  []
 opts_rw             XML::Compile::Cache  <some>
 opts_writers        XML::Compile::Cache  []
 prefixes                             undef
 schema_dirs         XML::Compile     undef
 typemap             XML::Compile::Schema  {}
 version                              <required>

. allow_undeclared => BOOLEAN

=over 4

In the optimal case, all types used in your application are declared
during the initiation phase of your program.  This will make it easy
to write a fast daemon application, or transform your program into a
daemon later.  So: "false" would be a good setting.  However, on the moment,
the developer of this module has no idea which types people will use.
Please help me with the specs!

All C<any> elements will be ATTEMPTed to be processed at run-time
by default.

The GML specification will require PREFIXED key rewrite, because the
complexity of namespaces is enormous.  Besides, mixed elements are
processed as STRUCTURAL by default (mixed in texts ignored).

=back

. any_element => CODE|'TAKE_ALL'|'SKIP_ALL'|'ATTEMPT'

. hook => ARRAY-WITH-HOOKDATA | HOOK

. hooks => ARRAY-OF-HOOK

. ignore_unused_tags => BOOLEAN|REGEXP

. key_rewrite => HASH|CODE|ARRAY-of-HASH-and-CODE

. opts_readers => HASH|ARRAY-of-PAIRS

. opts_rw => HASH|ARRAY-of-PAIRS

. opts_writers => HASH|ARRAY-of-PAIRS

. prefixes => ARRAY|HASH

=over 4

Prefix abbreviations, to be used by cache object.  Which prefixes are
defined depends on the schema version.

=back

. schema_dirs => DIRECTORY|ARRAY-OF-DIRECTORIES

. typemap => HASH

. version => VERSION|NAMESPACE

=over 4

Only used when the object is created directly from this base-class.  It
determines which GML syntax is to be used.  Can be a VERSION like "3.1.1"
or a NAMESPACE URI like 'NS_GML_300'.

=back

=back

=head2 Accessors

$obj-E<gt>B<addHook>(HOOKDATA|HOOK|undef)

=over 4

See L<XML::Compile::Schema/"Accessors">

=back

$obj-E<gt>B<addHooks>(HOOK, [HOOK, ...])

=over 4

See L<XML::Compile::Schema/"Accessors">

=back

$obj-E<gt>B<addKeyRewrite>(CODE|HASH, CODE|HASH, ...)

=over 4

See L<XML::Compile::Schema/"Accessors">

=back

$obj-E<gt>B<addSchemaDirs>(DIRECTORIES|FILENAME)

Geo::GML-E<gt>B<addSchemaDirs>(DIRECTORIES|FILENAME)

=over 4

See L<XML::Compile/"Accessors">

=back

$obj-E<gt>B<addSchemas>(XML, OPTIONS)

=over 4

See L<XML::Compile::Schema/"Accessors">

=back

$obj-E<gt>B<addTypemap>(PAIR)

=over 4

See L<XML::Compile::Schema/"Accessors">

=back

$obj-E<gt>B<addTypemaps>(PAIRS)

=over 4

See L<XML::Compile::Schema/"Accessors">

=back

$obj-E<gt>B<allowUndeclared>([BOOLEAN])

=over 4

See L<XML::Compile::Cache/"Accessors">

=back

$obj-E<gt>B<direction>

=over 4

Returns 'READER', 'WRITER', or 'RW'.

=back

$obj-E<gt>B<hooks>

=over 4

See L<XML::Compile::Schema/"Accessors">

=back

$obj-E<gt>B<prefix>(PREFIX)

=over 4

See L<XML::Compile::Cache/"Accessors">

=back

$obj-E<gt>B<prefixFor>(URI)

=over 4

See L<XML::Compile::Cache/"Accessors">

=back

$obj-E<gt>B<prefixes>([PAIRS|ARRAY|HASH])

=over 4

See L<XML::Compile::Cache/"Accessors">

=back

$obj-E<gt>B<version>

=over 4

GML version, for instance '3.2.1'.

=back

=head2 Compilers

$obj-E<gt>B<compile>(('READER'|'WRITER'), TYPE, OPTIONS)

=over 4

See L<XML::Compile::Schema/"Compilers">

=back

$obj-E<gt>B<compileAll>(['READER'|'WRITER'|'RW', [NAMESPACE]])

=over 4

See L<XML::Compile::Cache/"Compilers">

=back

$obj-E<gt>B<dataToXML>(NODE|REF-XML-STRING|XML-STRING|FILENAME|FILEHANDLE|KNOWN)

=over 4

See L<XML::Compile/"Compilers">

=back

$obj-E<gt>B<reader>(TYPE|NAME, OPTIONS)

=over 4

See L<XML::Compile::Cache/"Compilers">

=back

$obj-E<gt>B<template>('PERL'|'XML', TYPE, OPTIONS)

=over 4

See L<XML::Compile::Schema::template()|XML::Compile::Schema/"Compilers">.  This will create an example
of the data-structure based on GML.  All OPTIONS are passed to the
template generator, the only reason to have this method, is to avoid
the need to collect all the GML XML files yourself.

 Option              --Defined in     --Default
 attributes_qualified  XML::Compile::Schema  <undef>
 elements_qualified    XML::Compile::Schema  <undef>
 include_namespaces    XML::Compile::Schema  <true>
 indent                XML::Compile::Schema  " "
 show_comments         XML::Compile::Schema  ALL

. attributes_qualified => BOOLEAN

. elements_qualified => C<ALL>|C<TOP>|C<NONE>|BOOLEAN

. include_namespaces => BOOLEAN

. indent => STRING

. show_comments => STRING|'ALL'|'NONE'

example: 

  use Geo::GML;
  use Geo::GML::Util     qw/NS_GML_321/;
  use XML::Compile::Util qw/pack_type/;
  my $gml   = Geo::GML->new(version => NS_GML_321);

  # to simplify the output, reducing often available large blocks
  my @types = qw/gml:MetaDataPropertyType gml:StringOrRefType
     gml:ReferenceType/;
  my %hook  = (type => \@collapse_types, replace => 'COLLAPSE');

  # generate the data-structure
  my $type  = 'gml:RectifiedGridCoverage';  # any element name
  print $gml->template(PERL => $type, hook => \%hook);

=back

$obj-E<gt>B<writer>(TYPE|NAME)

=over 4

See L<XML::Compile::Cache/"Compilers">

=back

=head2 Helpers

$obj-E<gt>B<GPtoGML>(OBJECT, OPTIONS)

=over 4

See L<Geo::GML::GeoPoint/"Helpers">

=back

=head2 Administration

$obj-E<gt>B<declare>('READER'|'WRITER'|'RW', TYPE|ARRAY-of-TYPES, OPTIONS)

=over 4

See L<XML::Compile::Cache/"Administration">

=back

$obj-E<gt>B<elements>

=over 4

See L<XML::Compile::Schema/"Administration">

=back

$obj-E<gt>B<findName>(NAME)

=over 4

See L<XML::Compile::Cache/"Administration">

=back

$obj-E<gt>B<findSchemaFile>(FILENAME)

=over 4

See L<XML::Compile/"Administration">

=back

$obj-E<gt>B<importDefinitions>(XMLDATA, OPTIONS)

=over 4

See L<XML::Compile::Schema/"Administration">

=back

$obj-E<gt>B<knownNamespace>(NAMESPACE|PAIRS)

Geo::GML-E<gt>B<knownNamespace>(NAMESPACE|PAIRS)

=over 4

See L<XML::Compile/"Administration">

=back

$obj-E<gt>B<namespaces>

=over 4

See L<XML::Compile::Schema/"Administration">

=back

$obj-E<gt>B<printIndex>([FILEHANDLE], OPTIONS)

=over 4

List all the elements which can be produced with the schema.  By default,
this only shows the elements and excludes the abstract elements from
the list.  The selected FILEHANDLE is the default to print to.

 Option       --Defined in         --Default
 show_declared  XML::Compile::Cache  <true>

. show_declared => BOOLEAN

=back

$obj-E<gt>B<types>

=over 4

See L<XML::Compile::Schema/"Administration">

=back

$obj-E<gt>B<walkTree>(NODE, CODE)

=over 4

See L<XML::Compile/"Administration">

=back

=head1 DETAILS

=head1 DIAGNOSTICS

Error: cannot find pre-installed name-space files

=over 4

Use C<$ENV{SCHEMA_LOCATION}> or L<new(schema_dirs)|XML::Compile/"Constructors"> to express location
of installed name-space files, which came with the L<XML::Compile|XML::Compile>
distribution package.

=back

Error: don't known how to interpret XML data

=over 4

=back

=head1 SEE ALSO

This module is part of Geo-GML distribution version 0.13,
built on January 21, 2009. Website: F<http://perl.overmeer.net/geo/>
All modules in this suite:
L</Geo::GML>,
L</Geo::ISO19139>,
L</Geo::EOP>,
L</Geo::Point>,
L</Geo::Proj4>,
L</Geo::WKT>, and
L</Math::Polygon>.

Please post questions or ideas to
F<http://geo-perl@list.hut.fi|the Geo-Perl mailinglist>

=head1 COPYRIGHTS

=head2 License of the CODE

Copyrights of the perl code and the related documentation by
2008-2009 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://www.perl.com/perl/misc/Artistic.html>

=head2 License of the SCHEMAS

The included schemas are copyrighted by the Open Geospatial Consortium, Inc.
They are unmodified copied from the files at F<http://schemas.opengis.net>.
Read OGCs disclaimer and copyright statements on documentation and software
at F<http://www.opengeospatial.org/ogc/legal>.  The license text is also
included in this CPAN distribution.

