python/google/appengine/api/search/geo_util.py

   1 #!/usr/bin/env python
   2 #
   3 # Copyright 2007 Google Inc.
   4 #
   5 # Licensed under the Apache License, Version 2.0 (the "License");
   6 # you may not use this file except in compliance with the License.
   7 # You may obtain a copy of the License at
   8 #
   9 #     http://www.apache.org/licenses/LICENSE-2.0
  10 #
  11 # Unless required by applicable law or agreed to in writing, software
  12 # distributed under the License is distributed on an "AS IS" BASIS,
  13 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  14 # See the License for the specific language governing permissions and
  15 # limitations under the License.
  16 #
  17 """Utilities to support geo fields on the Python dev server."""
  18
  19 import math
  20
  21
  22 class LatLng(object):
  23   """A class representing a Latitude/Longitude pair."""
  24
  25   _EARTH_RADIUS_METERS = 6371010
  26
  27   def __init__(self, latitude, longitude):
  28     """Initializer.
  29
  30     Args:
  31       latitude: The latitude in degrees.
  32       longitude: The longitude in degrees.
  33
  34     Raises:
  35       TypeError: If a non-numeric latitude or longitude is passed.
  36     """
  37     self._lat = latitude
  38     self._lng = longitude
  39
  40   @property
  41   def latitude(self):
  42     """Returns the latitude in degrees."""
  43     return self._lat
  44
  45   @property
  46   def longitude(self):
  47     """Returns the longitude in degrees."""
  48     return self._lng
  49
  50   def __sub__(self, other):
  51     """Subtraction.
  52
  53     Args:
  54       other: the LatLng which this LatLng is subtracted by.
  55
  56     Returns:
  57       the great circle distance between two LatLng objects as computed
  58       by the Haversine formula.
  59     """
  60
  61     assert isinstance(other, LatLng)
  62
  63     lat_rad = math.radians(self._lat)
  64     lng_rad = math.radians(self._lng)
  65     other_lat_rad = math.radians(other.latitude)
  66     other_lng_rad = math.radians(other.longitude)
  67
  68     dlat = lat_rad - other_lat_rad
  69     dlng = lng_rad - other_lng_rad
  70     a1 = math.sin(dlat / 2)**2
  71     a2 = math.cos(lat_rad) * math.cos(other_lat_rad) * math.sin(dlng / 2)**2
  72     return 2 * self._EARTH_RADIUS_METERS * math.asin(math.sqrt(a1 + a2))