Create polyline.py

polyline decoder

polyline.py

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+# This function is free of any dependencies.
+# source: https://github.com/mgd722/decode-google-maps-polyline
+def decode_polyline(polyline_str):
+    '''Pass a Google Maps encoded polyline string; returns list of lat/lon pairs'''
+    index, lat, lng = 0, 0, 0
+    coordinates = []
+    changes = {'latitude': 0, 'longitude': 0}
+
+    # Coordinates have variable length when encoded, so just keep
+    # track of whether we've hit the end of the string. In each
+    # while loop iteration, a single coordinate is decoded.
+    while index < len(polyline_str):
+        # Gather lat/lon changes, store them in a dictionary to apply them later
+        for unit in ['latitude', 'longitude']: 
+            shift, result = 0, 0
+
+            while True:
+                byte = ord(polyline_str[index]) - 63
+                index+=1
+                result |= (byte & 0x1f) << shift
+                shift += 5
+                if not byte >= 0x20:
+                    break
+
+            if (result & 1):
+                changes[unit] = ~(result >> 1)
+            else:
+                changes[unit] = (result >> 1)
+
+        lat += changes['latitude']
+        lng += changes['longitude']
+
+        coordinates.append((lat / 100000.0, lng / 100000.0))
+
+    return coordinates