Geo::Hex1 - Convert between latitude/longitude and GeoHex code version 1

    use Geo::Hex1;

    # From latitude/longitude to hex code

    my $code = latlng2geohex( $lat, $lng, $level );

    # From hex code to center latitude/longitude

    my ( $center_lat, $center_lng, $level ) = geohex2latlng( $code );

    # From hex code to hex polygon

    my $poly = geohex2polygon( $code );

    my ( $wlat,  $wlng  ) = @{$poly->[0]}; # West point
    my ( $nwlat, $nwlng ) = @{$poly->[1]}; # North west point
    my ( $nelat, $nelng ) = @{$poly->[2]}; # North east point
    my ( $elat,  $elng  ) = @{$poly->[3]}; # East point
    my ( $selat, $selng ) = @{$poly->[4]}; # South east point
    my ( $swlat, $swlng ) = @{$poly->[5]}; # South west point
    my ( $wlat,  $wlng  ) = @{$poly->[6]}; # West point again ( Same with 0 )

    # Get hex distance between two hex codes

    my $dist = geohex2distance('wknR','wkmO'); # 3

    # Get all hex codes list include in given hex distance

    my $list = distance2geohexes('8sijg',2); 
    foreach my $code (@{$list}) { print $code . "\n" }
    # 8sijh
    # 8siig
    # 8siif
    # 8sijf
    # 8sikg
    # 8sikh
    # 8sili
    # 8siki
    # 8siji
    # 8siih
    # 8sihg
    # 8sihf
    # 8sihe
    # 8siie
    # 8sije
    # 8sikf
    # 8silg
    # 8silh

package Geo::Hex1;

use warnings;
use strict;
use Carp;

use POSIX       qw/floor ceil/;
use Math::Round qw/round/;

use version; our $VERSION = qv('0.0.2');
use vars qw(@ISA @EXPORT);
use Exporter;
@ISA    = qw(Exporter);
@EXPORT = qw(latlng2geohex geohex2latlng geohex2polygon geohex2distance distance2geohexes);

# Constants

my $h_key       = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWX';
my @h_key       = split( //, $h_key );
my $h_customize = 0;
my $h_grid      = 1000;
my $h_size      = 0.5;
my $min_x_lon   = 122930; #与那国島
my $min_x_lat   = 24448;
my $min_y_lon   = 141470; #南硫黄島
my $min_y_lat   = 24228;

# Some internal functions

sub __geohex2level {
    my $code = shift;
    
    my @code     = split( //, $code );
    my $c_length = @code or croak 'GeoHex code must be set';
    my $level;

    if ( $c_length > 4 ) {
        $level = index( $h_key, shift @code );
        croak 'Code format is something wrong' if ( $level == -1 );
        $level = 60 if ( $level == 0 );
    } else {
        $level = 7;
    }
    return ( $level, $c_length, @code );
}

sub __geohex2hyhx {
    my $code = shift;

    my ( $level, $c_length, @code ) = eval { __geohex2level( $code ) };
    croak $@ if ( $@ );

    my $unit_x = 6.0 * $level * $h_size;
    my $unit_y = 2.8 * $level * $h_size;
    my $h_k    = ( round( ( 1.4 / 3 ) * $h_grid ) ) / $h_grid;
    my $base_x = floor( ( $min_x_lon + $min_x_lat / $h_k ) / $unit_x );
    my $base_y = floor( ( $min_y_lat - $h_k * $min_y_lon ) / $unit_y );

    my ( $h_x, $h_y );
    if ( $c_length > 5 ) {
        $h_x = index( $h_key, $code[0] ) * 3600 + index( $h_key, $code[2] ) * 60 + index( $h_key, $code[4] );
        $h_y = index( $h_key, $code[1] ) * 3600 + index( $h_key, $code[3] ) * 60 + index( $h_key, $code[5] );
    } else {
        $h_x = index( $h_key, $code[0] ) * 60   + index( $h_key, $code[2] );
        $h_y = index( $h_key, $code[1] ) * 60   + index( $h_key, $code[3] );
    }
    
    return ( $h_y, $h_x, $level, $unit_x, $unit_y, $h_k, $base_x, $base_y );
}

sub __hyhx2geohex {
    my ( $h_y, $h_x, $level ) = @_;

    my $h_x_100 = floor( $h_x / 3600);
    my $h_x_10  = floor(($h_x % 3600) / 60);
    my $h_x_1   = floor(($h_x % 3600) % 60);
    my $h_y_100 = floor( $h_y / 3600);
    my $h_y_10  = floor(($h_y % 3600) / 60);
    my $h_y_1   = floor(($h_y % 3600) % 60);

    my $code;
    if ( $level < 7 ) {
        $code = $h_key[ $level % 60 ] . $h_key[ $h_x_100 ] . $h_key[ $h_y_100 ] . $h_key[ $h_x_10 ] . $h_key[ $h_y_10 ] . $h_key[ $h_x_1 ] . $h_key[ $h_y_1 ];
    } elsif ( $level == 7 ) {
        $code = $h_key[ $h_x_10 ] . $h_key[ $h_y_10 ] . $h_key[ $h_x_1 ] . $h_key[ $h_y_1 ];
    } else {
        $code = $h_key[ $level % 60 ] . $h_key[ $h_x_10 ] . $h_key[ $h_y_10 ] . $h_key[ $h_x_1 ] . $h_key[ $h_y_1 ];
    }
    return $code;
}

# Export function for GeoHex

sub latlng2geohex {
    my $lat   = shift;
    my $lon   = shift;
    my $level = shift;

    $level = defined( $level ) ? $level : 7;
    croak 'Level must be between 1 and 60' if ( $level !~ /^\d+$/ || $level < 1 || $level > 60 );

    my $lon_grid = $lon * $h_grid;
    my $lat_grid = $lat * $h_grid;
    my $unit_x   = 6.0  * $level * $h_size;
    my $unit_y   = 2.8  * $level * $h_size;
    my $h_k      = ( round( (1.4 / 3) * $h_grid) ) / $h_grid;
    my $base_x   = floor( ($min_x_lon + $min_x_lat / $h_k      ) / $unit_x);
    my $base_y   = floor( ($min_y_lat - $h_k       * $min_y_lon) / $unit_y);
    my $h_pos_x  = ( $lon_grid + $lat_grid / $h_k     ) / $unit_x - $base_x;
    my $h_pos_y  = ( $lat_grid - $h_k      * $lon_grid) / $unit_y - $base_y;
    my $h_x_0    = floor($h_pos_x);
    my $h_y_0    = floor($h_pos_y);
    my $h_x_q    = floor(($h_pos_x - $h_x_0) * 100) / 100;
    my $h_y_q    = floor(($h_pos_y - $h_y_0) * 100) / 100;
    my $h_x      = round($h_pos_x);
    my $h_y      = round($h_pos_y);
    if ( $h_y_q > -$h_x_q + 1 ) {
        if( ($h_y_q < 2 * $h_x_q ) && ( $h_y_q > 0.5 * $h_x_q ) ){
            $h_x = $h_x_0 + 1;
            $h_y = $h_y_0 + 1;
       }
    } elsif ( $h_y_q < -$h_x_q + 1 ) {
        if( ($h_y_q > (2 * $h_x_q ) - 1 ) && ( $h_y_q < ( 0.5 * $h_x_q ) + 0.5 ) ) {
            $h_x = $h_x_0;
            $h_y = $h_y_0;
        }
    }

    return __hyhx2geohex( $h_y, $h_x, $level );
}

sub geohex2latlng{
    my $code = shift;

    my ( $lat, $lon );
    my ( $h_y, $h_x, $level, $unit_x, $unit_y, $h_k, $base_x, $base_y ) = eval { __geohex2hyhx( $code ) };
    croak $@ if ( $@ );
    
    my $h_lat = ( $h_k   * ( $h_x + $base_x ) * $unit_x + ( $h_y + $base_y ) * $unit_y ) / 2;
    my $h_lon = ( $h_lat - ( $h_y + $base_y ) * $unit_y ) / $h_k;
    $lat      = $h_lat / $h_grid;
    $lon      = $h_lon / $h_grid;

    return ( $lat, $lon, $level );
}


sub geohex2polygon{
    my $code = shift;
    my ( $lat, $lon, $level ) = geohex2latlng( $code );

    my $d = $level * $h_size / $h_grid;
    
    return [
        [ $lat           , $lon - 2.0 * $d ],
        [ $lat + 1.4 * $d, $lon - 1.0 * $d ],
        [ $lat + 1.4 * $d, $lon + 1.0 * $d ],
        [ $lat           , $lon + 2.0 * $d ],
        [ $lat - 1.4 * $d, $lon + 1.0 * $d ],
        [ $lat - 1.4 * $d, $lon - 1.0 * $d ],
        [ $lat           , $lon - 2.0 * $d ],
    ];
}

sub geohex2distance {
    my ( $code1, $code2 ) = @_;
    
    my ( $h_y1, $h_x1, $level1 ) = eval { __geohex2hyhx( $code1 ) };
    croak $@ if ( $@ );
    my ( $h_y2, $h_x2, $level2 ) = eval { __geohex2hyhx( $code2 ) };
    croak $@ if ( $@ );
    croak 'Level of codes are must same value' unless ( $level1 == $level2 );
    
    my $dh_y = $h_y1 - $h_y2;
    my $dh_x = $h_x1 - $h_x2;
    my $ah_y = abs( $dh_y );
    my $ah_x = abs( $dh_x );
        
    if ( $dh_y * $dh_x > 0 ) {
        return $ah_x > $ah_y ? $ah_x : $ah_y;
    } else {
        return $ah_x + $ah_y;
    }
}

sub distance2geohexes {
    my ( $code, $dist ) = @_;
    
    my ( $h_y, $h_x, $level ) = eval { __geohex2hyhx( $code ) };
    croak $@ if ( $@ );
    
    my @results;
    foreach my $d_y ( -1 * $dist .. $dist ) {
        my $dh_y  = $h_y + $d_y;
        my $dmn_x = $d_y > 0 ? -1 * $dist + $d_y : -1 * $dist;
        my $dmx_x = $d_y < 0 ? $dist + $d_y      : $dist;
        
        foreach my $d_x ( $dmn_x .. $dmx_x ) {
            next if ( $d_y == 0 && $d_x == 0 );
        
            push @results, __hyhx2geohex( $h_y + $d_y, $h_x + $d_x, $level );
        }
    }
    
    return \@results;
}

1; # Magic true value required at end of module
__END__