Polyline decoder

server/lib/python/cartodb_services/cartodb_services/tools/__init__.py

@@ -1,2 +1,3 @@
 from redis_tools import RedisConnection
-from coordinates import Coordinate
+from coordinates import Coordinate
+from polyline import PolyLine

server/lib/python/cartodb_services/cartodb_services/tools/polyline.py

@@ -0,0 +1,51 @@
+from itertools import tee, izip
+from math import trunc
+
+
+class PolyLine:
+    """ Polyline decoder https://developers.google.com/maps/documentation/utilities/polylinealgorithm?csw=1 """
+
+    def decode(self, data):
+        coordinates = []
+        chunks = self._extract_chunks(data)
+        for chunk in chunks:
+            coordinate = self._process_chunk(chunk)
+            coordinate /= 1e5
+            print coordinate
+            if len(coordinates) > 1:
+                # We have to sum the previous with the offset in this chunk
+                coordinate += coordinates[-2]
+            coordinates.append(round(coordinate, 5))
+
+        print coordinates
+
+        return zip(coordinates, coordinates[1:])[::2]
+
+    def _extract_chunks(self, data):
+        chunks, chunk = [], []
+        for character in data:
+            byte = ord(character) - 63
+            if byte & 0x20 > 0:
+                byte &= 0x1F
+                chunk.append(byte)
+            else:
+                chunk.append(byte)
+                chunks.append(chunk)
+                chunk = []
+
+        return chunks
+
+    def _process_chunk(self, chunk):
+        coordinate = self._get_coordinate(chunk)
+        # Check if the coordinate is negative
+        if coordinate & 0x1:
+            return ~(coordinate >> 1)
+        else:
+            return coordinate >> 1
+
+    def _get_coordinate(self, chunk):
+        coordinate = 0
+        for i, c in enumerate(chunk):
+            coordinate |= c << (i * 5)
+
+        return coordinate