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package Geo::Hash;
use warnings;
use strict;
use Carp;
=head1 NAME
Geo::Hash - Encode / decode geohash.org locations.
=head1 VERSION
This document describes Geo::Hash version 0.02
=cut
our $VERSION = '0.02';
=head1 SYNOPSIS
use Geo::Hash;
my $gh = Geo::Hash->new;
my $hash = $gh->encode( $lat, $lon );
my ( $lat, $lon ) = $gh->decode( $hash );
=head1 DESCRIPTION
Geohash is a latitude/longitude geocode system invented by Gustavo
Niemeyer when writing the web service at geohash.org, and put into the
public domain.
This module encodes and decodes geohash locations.
See L<http://en.wikipedia.org/wiki/Geohash> and L<http://geohash.org>
for more information.
=head1 INTERFACE
=head2 C<< new >>
Create a new Geo::Hash object.
my $gh = Geo::Hash->new;
=cut
sub new { bless {}, shift }
my @ENC = qw(
0 1 2 3 4 5 6 7 8 9 b c d e f g h j k m n p q r s t u v w x y z
);
my %DEC = map { $ENC[$_] => $_ } 0 .. $#ENC;
sub _mid {
my ( $ar, $wh ) = @_;
return ( $ar->[$wh][0] + $ar->[$wh][1] ) / 2;
}
# The number of bits necessary to represent the specified number of
# decimal digits
sub _d2b { int( shift() * 3.32192809488736 + 1 ) }
sub _bits_for_number {
my $n = shift;
return 0 unless $n =~ s/.*\.//;
return _d2b( length $n );
}
=head2 C<< precision >>
Infer a suitable precision (number of character in hash) for a given
lat, lon pair.
my $prec = $gh->precision( $lat, $lon );
=cut
sub precision {
my ( $self, $lat, $lon ) = @_;
my $lab = _bits_for_number( $lat ) + 8;
my $lob = _bits_for_number( $lon ) + 9;
return int( ( ( $lab > $lob ? $lab : $lob ) + 1 ) / 2.5 );
}
=head2 C<< encode >>
Encode a lat, long pair into a geohash.
my $hash = $gh->encode( $lat, $lon );
You may optionally supply the length of the desired geohash:
# Very precise
my $hash = $gh->encode( $lat, $lon, 10 );
If the precision argument is omitted C<precision> will be used to
provide a default.
=cut
sub encode {
croak "encode needs two or three arguments"
unless @_ >= 3 && @_ <= 4;
my ( $self, @pos ) = splice @_, 0, 3;
my $prec = shift || $self->precision( @pos );
my $int = [ [ 90, -90 ], [ 180, -180 ] ];
my $flip = 1;
my @enc = ();
while ( @enc < $prec ) {
my $bits = 0;
for ( 0 .. 4 ) {
my $mid = _mid( $int, $flip );
my $bit = $pos[$flip] >= $mid ? 1 : 0;
$bits = ( ( $bits << 1 ) | $bit );
$int->[$flip][$bit] = $mid;
$flip ^= 1;
}
push @enc, $ENC[$bits];
}
return join '', @enc;
}
=head2 C<< decode_to_interval >>
Like C<decode> but instead of returning a pair of coordinates returns
the interval for each coordinate. This gives some indication of how
precisely the original hash specified the location.
The return value is a pair of array refs. Each referred to array
contains the upper and lower bounds for each coordinate.
my ( $lat_range, $lon_range ) = $gh->decode_to_interval( $hash );
# $lat_range and $lon_range are references to two element arrays
=cut
sub decode_to_interval {
croak "Needs one argument"
unless @_ == 2;
my ( $self, $hash ) = @_;
my $int = [ [ 90, -90 ], [ 180, -180 ] ];
my $flip = 1;
for my $ch ( split //, $hash ) {
if ( defined( my $bits = $DEC{$ch} ) ) {
for ( 0 .. 4 ) {
$int->[$flip][ ( $bits & 16 ) >> 4 ]
= _mid( $int, $flip );
$flip ^= 1;
$bits <<= 1;
}
}
else {
croak "Bad character '$ch' in hash '$hash'";
}
}
return @$int;
}
=head2 C<< decode >>
Decode a geohash into a lat, long pair.
my ( $lat, $lon ) = $gh->decode( $hash );
=cut
sub decode {
my @int = shift->decode_to_interval( @_ );
return map { _mid( \@int, $_ ) } 0 .. 1;
}
1;
__END__
=head1 CONFIGURATION AND ENVIRONMENT
Geo::Hash requires no configuration files or environment variables.
=head1 DEPENDENCIES
None.
=head1 INCOMPATIBILITIES
None reported.
=head1 BUGS AND LIMITATIONS
No bugs have been reported.
Please report any bugs or feature requests to
C<bug-geo-hash@rt.cpan.org>, or through the web interface at
L<http://rt.cpan.org>.
=head1 AUTHOR
Andy Armstrong C<< <andy@hexten.net> >>
L<http://geohash.org/gcwrdtsvrfgr>
=head1 LICENCE AND COPYRIGHT
Copyright (c) 2008, Andy Armstrong C<< <andy@hexten.net> >>.
This module is free software; you can redistribute it and/or
modify it under the same terms as Perl itself. See L<perlartistic>.
|
