use OSM for sharing link, fixes #46

poor/util.py

@@ -246,14 +246,15 @@ def format_distance_and_bearing(meters, bearing, n=2, short=True):
 
 def format_location_message(x, y, html=False):
     """Format coordinates of a point into a location message."""
+    osm_url = short_osm(y,x)
     if html:
         return ('<a href="geo:{y:.5f},{x:.5f}">geo:{y:.5f},{x:.5f}</a><br>'
-                '<a href="http://maps.google.com/?q={y:.5f},{x:.5f}">'
-                'http://maps.google.com/?q={y:.5f},{x:.5f}</a>'
-                .format(x=x, y=y))
+                '<a href="{osm}">'
+                '{osm}</a>'
+                .format(x=x, y=y, osm=osm_url))
     else:
         return ('geo:{y:.5f},{x:.5f} '
-                'http://maps.google.com/?q={y:.5f},{x:.5f}'
+                '{osm}'
                 .format(x=x, y=y))
 
 def format_time(seconds):
@@ -465,3 +466,63 @@ def write_json(data, path):
               .format(repr(path), str(error)),
               file=sys.stderr)
         raise # Exception
+
+######################################################################################
+## Utility functions from external sources
+######################################################################################
+
+## OSM schort link, from https://gist.github.com/mdornseif/5652824
+# osm_shortlink.py - MAximillian Dornseif 2013 - Public Domain
+# see http://wiki.openstreetmap.org/wiki/Shortlink
+# https://github.com/openstreetmap/openstreetmap-website/blob/master/lib/short_link.rb
+# and makeShortCode in
+# https://github.com/openstreetmap/openstreetmap-website/blob/master/app/assets/javascripts/application.js
+
+# array of 64 chars to encode 6 bits. this is almost like base64 encoding, but
+# the symbolic chars are different, as base64's + and / aren't very
+# URL-friendly.
+ARRAY = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789_~'
+
+import math
+
+def short_osm(lat, lon, zoom=16):
+    """Return a short link representing a location in OpenStreetmap.
+
+    Provide coordinates and optional zoom level. e.g.:
+
+    >>> short_osm(50.671530961990356, 6.09715461730957)
+    http://osm.org/go/0GAjIv8h
+    >>> short_osm(0, 0, 3)
+    http://osm.org/go/wAAA--
+    >>> short_osm(0, 0, 4)
+    http://osm.org/go/wAAA
+    """
+
+    def _encode(lat, lon, z):
+        """given a location and zoom, return a short string representing it."""
+        x = int((lon + 180.0) * 2**32 / 360.0)
+        y = int((lat +  90.0) * 2**32 / 180.0)
+        code = _interleave(x, y)
+        str = ''
+        # add eight to the zoom level, which approximates an accuracy of
+        # one pixel in a tile.
+        for i in range(int(math.ceil((z + 8) / 3.0))):
+            digit = (code >> (56 - 6 * i)) & 0x3f;
+            str += ARRAY[digit]
+        # append characters onto the end of the string to represent
+        # partial zoom levels (characters themselves have a granularity
+        # of 3 zoom levels).
+        for i in range((z + 8) % 3):
+            str += "-"
+        return str
+
+
+    def _interleave(x, y):
+        """combine 2 32 bit integers to a 64 bit integer"""
+        c = 0
+        for i in range(31, 0, -1):
+          c = (c << 1) | ((x >> i) & 1)
+          c = (c << 1) | ((y >> i) & 1)
+        return c
+
+    return 'http://osm.org/go/' + _encode(lat, lon, zoom) + "?m"