Merge remote-tracking branch 'mysociety/add-osm-link-to-email'

1 files changed, 44 insertions, 0 deletions

diff --git a/perllib/Utils/OpenStreetMap.pm b/perllib/Utils/OpenStreetMap.pm
new file mode 100644
index 000000000..900569a77
--- /dev/null
+++ b/perllib/Utils/OpenStreetMap.pm
@@ -0,0 +1,44 @@
+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;