GeoLocation.js

//Javascript for finding latitude and longitude range boundaries.
//Based on the excellent Java example by http://janmatuschek.de/LatitudeLongitudeBoundingCoordinates

(function(){

var GeoLocation = GeoLocation ? GeoLocation : {
  TO_RADIAN: 0.0174532925,
  TO_DEGREE: 57.2957795,
  EARTH_RADIUS: 6371.01,
  TO_MILE: 0.621371192,
  TO_KM: 1.609344,
  MIN_LAT: function() { return GeoLocation.degreeToRadian(-90) },
  MAX_LAT: function() { return GeoLocation.degreeToRadian(90) },  
  MIN_LON: function() { return GeoLocation.degreeToRadian(-180) },  
  MAX_LON: function() { return GeoLocation.degreeToRadian(180) },  
  
  degreeToRadian: function (degree) { return degree * GeoLocation.TO_RADIAN },
  radianToDegree: function (radian) { return radian * GeoLocation.TO_DEGREE },
  kmToMile: function (km) {return km * GeoLocation.TO_MILE },
  mileToKm: function (mile) {return mile * GeoLocation.TO_KM },

  buildLocationRange: function(latitude, longitude, boundaryInMiles) {
    var degLat = latitude;
    var degLon = longitude;
    var radLat = GeoLocation.degreeToRadian(degLat);
    var radLon = GeoLocation.degreeToRadian(degLon);
    
    var location = {  degLat: degLat
                    , degLon: degLon
                    , radLat: radLat
                    , radLon: radLon
                   };

    GeoLocation.checkBounds(location);
    var locationRange = GeoLocation.boundingCoordinates(location, GeoLocation.mileToKm(boundaryInMiles));
    
    return locationRange;
  },
  
  checkBounds: function(location) {
    if (location.radLat < GeoLocation.MIN_LAT || location.radLat > GeoLocation.MAX_LAT ||
        location.radLon < GeoLocation.MIN_LON || location.radLon > GeoLocation.MAX_LON) {
          console.log("radLat or radLon is out of bounds");
    }  
  },
  
  distance: function(location1, location2) {
    return Math.acos(Math.sin(location1.radLat) * Math.sin(location2.radLat) +
        Math.cos(location1.radLat) * Math.cos(location2.radLat) *
        Math.cos(location1.radLon - location2.radLon)) * GeoLocation.EARTH_RADIUS;
  },
  
  boundingCoordinates: function(location, distance) {
    if (!location || distance < 0) {
      console.log("no location or distance");
      return;
    }
    
    var radius = GeoLocation.EARTH_RADIUS;
    var radDist = distance / radius;
    var minLat = location.radLat - radDist;
    var maxLat = location.radLat + radDist;

    var minLon, maxLon;
    
    if (minLat > GeoLocation.MIN_LAT() && maxLat < GeoLocation.MAX_LAT()) {
      var deltaLon = Math.asin(Math.sin(radDist) / Math.cos(location.radLat));
      minLon = location.radLon - deltaLon;
      if (minLon < GeoLocation.MIN_LON()) minLon += 2 * Math.PI;
      maxLon = location.radLon + deltaLon;
      if (maxLon > GeoLocation.MAX_LON()) maxLon -= 2 * Math.PI;
    } else {
      // a pole is within the distance
      minLat = Math.max(minLat, GeoLocation.MIN_LAT());
      maxLat = Math.min(maxLat, GeoLocation.MAX_LAT());
      minLon = GeoLocation.MIN_LON();
      maxLon = GeoLocation.MAX_LON();
    }
    
    var locationRange = {  lat: location.degLat
                      , lon: location.degLon
                      , minLat: GeoLocation.radianToDegree(minLat)
                      , maxLat: GeoLocation.radianToDegree(maxLat)
                      , minLon: GeoLocation.radianToDegree(minLon)
                      , maxLon: GeoLocation.radianToDegree(maxLon)
                     };
    return locationRange;
  }  
  
}

if (typeof exports !== 'undefined') {
  exports.GeoLocation = GeoLocation;
}  

})();