Polyline decoder

.gitignore

@@ -1,2 +1,5 @@
 .DS_Store
 *.pyc
+cartodb_services.egg-info/
+build/
+dist/

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

@@ -1,2 +1,3 @@
 from redis_tools import RedisConnection
 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

server/lib/python/cartodb_services/test/test_polyline.py

@@ -0,0 +1,39 @@
+from cartodb_services.tools import PolyLine
+from unittest import TestCase
+
+
+class TestPolyline(TestCase):
+
+    def setUp(self):
+        self.polyline = PolyLine()
+
+    def test_should_decode_a_chunk_correctly(self):
+        decoded_polyline = self.polyline.decode('`~oia@`~oia@')
+        original_value = [(-179.98321, -179.98321)]
+
+        assert decoded_polyline == original_value
+
+    def test_should_decode_polyline_correctly(self):
+        original_polyline_1 = [(38.5, -120.2),
+                             (40.7, -120.95),
+                             (43.252, -126.453)]
+        decoded_polyline_1 = self.polyline.decode('_p~iF~ps|U_ulLnnqC_mqNvxq`@')
+
+        assert decoded_polyline_1 == original_polyline_1
+
+        original_polyline_2 = [(17.95783,-5.58105),
+                             (15.79225,2.90039),
+                             (7.60211,-10.76660)]
+        decoded_polyline_2 = self.polyline.decode('mkrlBp`aa@z}eL_pwr@js~p@tilrA')
+
+        assert decoded_polyline_2 == original_polyline_2
+
+        original_polyline_3 = [(62.75473,-157.14844),
+                             (65.07213,169.80469) ,
+                             (48.92250,158.55469),
+                             (44.33957,-150.46875)]
+        decoded_polyline_3 = self.polyline.decode('ax_~Jv`d~\wrcMa`qj}@dfqaBngtcAhb~Zncc}y@')
+
+        assert decoded_polyline_3 == original_polyline_3
+
+