import itertools
import six
import math
class PolylineCodec(object):
def _pcitr(self, iterable):
return six.moves.zip(iterable, itertools.islice(iterable, 1, None))
def _py2_round(self, x):
# The polyline algorithm uses Python 2's way of rounding
return int(math.copysign(math.floor(math.fabs(x) + 0.5), x))
def _write(self, output, curr_value, prev_value, factor):
curr_value = self._py2_round(curr_value * factor)
prev_value = self._py2_round(prev_value * factor)
coord = curr_value - prev_value
coord <<= 1
coord = coord if coord >= 0 else ~coord
while coord >= 0x20:
output.write(six.unichr((0x20 | (coord & 0x1f)) + 63))
coord >>= 5
output.write(six.unichr(coord + 63))
def _trans(self, value, index):
byte, result, shift = None, 0, 0
while byte is None or byte >= 0x20:
byte = ord(value[index]) - 63
index += 1
result |= (byte & 0x1f) << shift
shift += 5
comp = result & 1
return ~(result >> 1) if comp else (result >> 1), index
def decode(self, expression, precision=5, geojson=False):
coordinates, index, lat, lng, length, factor = [], 0, 0, 0, len(expression), float(10 ** precision)
while index < length:
lat_change, index = self._trans(expression, index)
lng_change, index = self._trans(expression, index)
lat += lat_change
lng += lng_change
coordinates.append((lat / factor, lng / factor))
if geojson is True:
coordinates = [t[::-1] for t in coordinates]
return coordinates
def encode(self, coordinates, precision=5, geojson=False):
if geojson is True:
coordinates = [t[::-1] for t in coordinates]
output, factor = six.StringIO(), int(10 ** precision)
self._write(output, coordinates[0][0], 0, factor)
self._write(output, coordinates[0][1], 0, factor)
for prev, curr in self._pcitr(coordinates):
self._write(output, curr[0], prev[0], factor)
self._write(output, curr[1], prev[1], factor)
return output.getvalue()
