Added destinationPoint function

README.md

@@ -4,7 +4,7 @@ GeoPoint represents a geographic point for node.js and the browser, and provides
 
 ## Installation
 
-    npm install geopoint 
+    npm install geopoint
 
 ## Usage
 
@@ -25,6 +25,7 @@ var GeoPoint = require('geopoint'),
 * `.longitude(inRadians)`: Return the point's longitude. By default, the longitude is in degrees, unless `inRadians` is `true`
 * `.distanceTo(point, inKilometers)`: Calculate the distance to another `GeoPoint` instance. By default, the distance is calculated in miles, unless `inKilometers` is `true`
 * `.boundingCoordinates(distance, radius, inKilometers)`: Calculates the bounding coordinates of `distance` from the point and returns an array with the SW and NE points of the bounding box . If `radius` is not provided, the radius of the Earth will be used. The distance is calculated in miles unless `inKilometers` is `true`
+* `.destinationPoint(distance, radius, inKilometers)`: Given a bearing, and distance, calculate the destina­tion `GeoPoint`. The distance is calculated in miles unless `inKilometers` is `true`
 
 ## Static Methods
 
@@ -40,7 +41,7 @@ The `GeoPoint` constructor is exposed via `window.GeoPoint`.
 ## Running Tests
 
 Cachetree tests require [Mocha](http://visionmedia.github.com/mocha/) and can be run with either `npm test`.  You can specify Mocha options, such as the reporter, by adding a [mocha.opts](http://visionmedia.github.com/mocha/#mocha.opts) file, which is ignored by git, to the `test` directory.
- 
+
 # Credits
 
 This library is derived from the code presented in [Finding Points Within a Distance of a Latitude/Longitude Using Bounding Coordinates](http://janmatuschek.de/LatitudeLongitudeBoundingCoordinates) by [Jan Philip Matuschek](http://janmatuschek.de/Contact).

geopoint.js

@@ -3,7 +3,7 @@
   *
   * This library is derived from the Java code originally published at
   * http://JanMatuschek.de/LatitudeLongitudeBoundingCoordinates
-  * 
+  *
   * @author Jan Philip Matuschek
   * @version 22 September 2010
   */
@@ -158,6 +158,34 @@
     return [new GeoPoint(minLat, minLon, true), new GeoPoint(maxLat, maxLon, true)];
   };
 
+  /**
+   * Get destination point from distance and bearing
+   *
+   * @param   {Number}    distance      distance from the point
+   * @param   {Number}    bearing       degrees from 0 to 360 (clockwise from north)
+   * @param   {Boolean}   inKilometers  true to return the distance in kilometers
+   * @return  {GeoPoint}  destina­tion point
+   */
+  GeoPoint.prototype.destinationPoint = function(distance, bearing, inKilometers) {
+    if (!isNumber(distance) || distance <= 0) {
+      throw new Error('Invalid distance');
+    }
+    if (bearing === true || bearing === false) {
+      inKilometers = bearing;
+      bearing = 0;
+    }
+    if(!isNumber(bearing)) bearing = 0;
+    bearing = bearing % 360;
+
+    var radius = inKilometers === true ? EARTH_RADIUS_KM : EARTH_RADIUS_MI;
+        lat = this.latitude(true),
+        lon = this.longitude(true),
+        radDist = distance / radius,
+        lat2 = Math.asin( Math.sin(lat)*Math.cos(radDist) + Math.cos(lat)*Math.sin(radDist)*Math.cos(bearing) ),
+        lon2 = lon + Math.atan2(Math.sin(bearing)*Math.sin(radDist)*Math.cos(lat), Math.cos(radDist)-Math.sin(lat)*Math.sin(lat2));
+    return new GeoPoint(lat2, lon2, true);
+  };
+
   /**
    * Convert degrees to radians
    *