[ 10.7685250292969 24.0294289818115 ]
[ 10.764576366333 24.0289633201904 ]
------
[ 11.8467422927246 22.0280153343506 ]
[ 11.8505748185425 22.0356987510986 ]
------
[ 10.3691293842163 22.0120664238281 ]
[ 10.3718005385742 22.0104366081543 ]
------
[ 10.9817528293457 22.6283695793457 ]
[ 10.974320052002 22.6306978874512 ]
------
[ 12.2627455496826 23.6263988487549 ]
[ 12.2549643609009 23.62430337146 ]
------
[ 13.0046296383057 23.9849582969971 ]
[ 13.0082298898315 23.9801852653809 ]
------
[ 12.3460158833618 23.0528201469727 ]
[ 12.3482224891357 23.0609692253418 ]
------
[ 13.6142335176392 24.0877530998535 ]
[ 13.619808100647 24.0818159141846 ]
------
[ 10.4141905968628 21.2074031425781 ]
[ 10.4150035568848 21.2060061577148 ]
------
[ 11.0738495861206 23.2290730705566 ]
[ 11.0661845344849 23.2240672081299 ]
[ 11.0827921463623 23.2314013786621 ]
------
[ 10.8340263796387 21.6198629234619 ]
[ 10.8307745395508 21.6281284172363 ]
[ 10.8416914312744 21.6245195396729 ]
------

##</code><code>##

#! perl -slw
use strict;
use Data::Dump qw[ pp ];
use List::Util qw[ reduce ];
use GD;

use constant {
    WHITE => 16777215,
    MinX => 10.318842, MaxX => 14.124424,
    MinY => 21.097507, MaxY => 24.912207,
};
use constant {
    SpanX => MaxX - MinX, SpanY => MaxY - MinY,
};

sub rgb2n{ unpack 'N', pack 'CCCC', 0, @_ }
sub n2rgb{ unpack 'xCCC', pack 'N', $_[0] }

our $POINTS ||= 300_000;

my @points = map [ MinX + rand( SpanX ), MinY + rand( SpanY ) ], 1 .. $POINTS;

## Normalise to our grid, scale by 1000 and integerise
my @scaled = map [
    int( ( $_->[ 0 ] - MinX ) * 1000 ),
    int( ( $_->[ 1 ] - MinY ) * 1000 ),
], @points;

my( $sizeX, $sizeY ) = ( int( SpanX * 1000 ), int( SpanY * 1000 ) );
my $img = GD::Image->new( $sizeX, $sizeY , 1 );
$img->filledRectangle( 0, 0, $sizeX, $sizeY, rgb2n( 255, 255, 255 ) );


my %groups;
for my $i ( 0 .. $#scaled ) {
    my $color = $img->getPixel( @{ $scaled[ $i ] } );
    if( $color != WHITE ) {
        push @{ $groups{ $color } }, $i;
    }
    else {
        $color = $i;
    }
    $img->filledEllipse( @{ $scaled[ $i ] }, 20, 20, $i );
}

## Save the image showing all points/circles
open IMG, '>:raw', '694790all.png' or die $!;
print IMG $img->png;
close IMG;
system 1, '694790all.png';

undef $img;

## Produce a file of clusters of points
open OUT, '>', '694790.groups' or die $!;
for my $key ( sort { $a <=> $b } keys %groups ) {
    print OUT "[ @{ $points[ $_ ] } ]" for $key, @{ $groups{ $key } };
    print OUT "------";
}
close OUT;

## Produce second image showing just the clustered points.
$img = GD::Image->new( $sizeX, $sizeY , 1 );
$img->filledRectangle( 0, 0, $sizeX, $sizeY, rgb2n( 255, 255, 255 ) );

for my $key ( sort { $a <=> $b } keys %groups ) {
    $img->filledEllipse( @{ $scaled[ $key ] }, 20, 20, $key );
    $img->filledEllipse( @{ $scaled[ $_ ] }, 20, 20, $key ) for @{ $groups{ $key } };
}

open IMG, '>:raw', '694790grouped.png' or die $!;
print IMG $img->png;
close IMG;
system 1, '694790grouped.png';


__END__
Latitude stats:
Minimum: 10.318842
Maximum: 14.124424
Mean: 11.24719
Standard Deviation: 0.805771


Longitude stats:
Minimum: 21.097507
Maximum: 24.912207
Mean: 22.474358
Standard Deviation: 0.974835