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package Utils::OpenStreetMap;
use strict;
use warnings;
use Exporter 'import';
use POSIX qw(ceil);
our @EXPORT_OK = qw(short_url);
my $chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789_~";
sub short_url {
my ($lat, $lon, $zoom) = @_;
$zoom ||= 16;
my $x = ($lon + 180) * 2**32 / 360;
my $y = ($lat + 90) * 2**32 / 180;
my $code = _interleave($x, $y);
my $str = '';
# add eight to the zoom level, which approximates an accuracy of
# one pixel in a tile
my $n = ceil(($zoom + 8) / 3) - 1;
for my $i (0..$n) {
my $digit = ($code >> (58 - 6 * $i)) & 0x3f;
$str .= substr($chars, $digit, 1);
}
# append characters onto the end of the string to represent
# partial zoom levels (characters themselves have a granularity
# of 3 zoom levels).
$str .= "-" x (($zoom + 8) % 3);
return "http://osm.org/go/$str";
}
sub _interleave {
my ($x, $y) = @_;
my $c = 0;
for (my $i=31; $i>=0; $i--) {
$c = ($c << 1) | (($x >> $i) & 1);
$c = ($c << 1) | (($y >> $i) & 1);
}
return $c;
}
1;
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