anchor.diff:      DistanceAngle * ?RADIUS_METERS.
   
   
  +% Returns the width of a latitudinal degree
  +% in meters for the given Latitude
  +latitudinal_width(Lat) ->
  +    LatRad = Lat * ?DEGREES_TO_RAD,
  +    111132.954 - 559.822 * math:cos(2.0 * LatRad) + 1.175 * math:cos(4.0 * LatRad).
  +
  +
   -ifdef(TEST).
   
   distance_test() ->
  
positive.code: %
  %%%
  -module(teles_geo_query).
  -export([query_within/2, query_around/3, query_nearest/3, distance/2]).
  -include_lib("rstar/include/rstar.hrl").
  
  -ifdef(TEST).
  
negative.code:     B = rstar_geometry:point2d(47.276, 120.576, undefined),
      ?assertEqual(17045.480008358903, distance(A, B)).
  
  latitudinal_width_test() ->
      ?assertEqual(110574, round(latitudinal_width(0))),
      ?assertEqual(110649, round(latitudinal_width(15))),
      ?assertEqual(111132, round(latitudinal_width(45))),
      ?assertEqual(111412, round(latitudinal_width(60))),
      ?assertEqual(111694, round(latitudinal_width(90))).
  
  -endif.
  