Converts the distance between the WGS 84 coordinates pointA and pointB to meters.

geo-distance.coffee

###
Converts the distance between the WGS 84 coordinates pointA and pointB to meters.
Ported from http://groups.google.com/group/sci.geo.satellite-nav/msg/0bfca0bf8a986395
with the suggested radii-calculation optimization.
###
module.exports.WGS84DegreesToMeters = (pointA, pointB)->
  radFactor = Math.PI/180
  [lat1, lon1] = [pointA[0]*radFactor, pointA[1]*radFactor]
  [lat2, lon2] = [pointB[0]*radFactor, pointB[1]*radFactor]

  # Semi-major axis of WGS 84 ellipsoid, in meters.
  a = 6378137.0
  # Squared eccentricity of WGS 84 ellipsoid.
  es = 6.694379990141320E-03
  dlon = lon2 - lon1
  dlat = lat2 - lat1
  avg_lat = (lat2 + lat1) / 2

  radii = Math.pow(Math.sin(avg_lat), 2)
  # Radius of parallel.
  rlon = a * Math.cos(avg_lat) / Math.sqrt(1 - es * radii)
  # Radius of meridian.
  rlat = a * (1 - es) / Math.pow(1 - es * radii, 1.5)
  x = dlon * rlon
  y = dlat * rlat

  # The distance between the points, in meters.
  Math.sqrt(x*x + y*y)

geo-distance.js

/*
Converts the distance between the WGS 84 coordinates pointA and pointB to meters.
Ported from http://groups.google.com/group/sci.geo.satellite-nav/msg/0bfca0bf8a986395
with the suggested optimization
*/
module.exports.WGS84DegreesToMeters = function(pointA, pointB) {
  var a, avg_lat, dlat, dlon, es, lat1, lat2, lon1, lon2, radFactor, radii, rlat, rlon, x, y, _ref, _ref2;
  radFactor = Math.PI / 180;
  _ref = [pointA[0] * radFactor, pointA[1] * radFactor], lat1 = _ref[0], lon1 = _ref[1];
  _ref2 = [pointB[0] * radFactor, pointB[1] * radFactor], lat2 = _ref2[0], lon2 = _ref2[1];
  a = 6378137.0;
  es = 6.694379990141320E-03;
  dlon = lon2 - lon1;
  dlat = lat2 - lat1;
  avg_lat = (lat2 + lat1) / 2;
  radii = Math.pow(Math.sin(avg_lat), 2);
  rlon = a * Math.cos(avg_lat) / Math.sqrt(1 - es * radii);
  rlat = a * (1 - es) / Math.pow(1 - es * radii, 1.5);
  x = dlon * rlon;
  y = dlat * rlat;
  return Math.sqrt(x * x + y * y);
};