Android google map 两点之间的距离

在Android google map中，有时候会碰到计算两地的距离，下面的辅助类就可以帮助你计算距离：

 public class DistanceHelper {
     /** Names for the units to use */
     public final static int KILOMETERS = 0;
     public final static int STATUTE_MILES = 1;
     public final static int NAUTICAL_MILES = 2;

     /** Radius of the Earth in the units above */
     private final static double EARTHS_RADIUS[] = { 6378.1, // Kilometers
             3963.1676, // Statue miles
             3443.89849 // Nautical miles
     };

     /** Conversion factor to convert from degrees to radians */
     private static final double DEGREES_TO_RADIANS = (180 / Math.PI);

     /**
      * Calculates the "length" of an arc between two points on a sphere given
      * the latitude & longitude of those points.
      *
      * @param aLat
      *            Latitude of point A
      * @param aLong
      *            Longitude of point A
      * @param bLat
      *            Latitude of point B
      * @param bLong
      *            Longitude of point B
      * @return
      */
     private static double calclateArc(double aLat, double aLong, double bLat,
             double bLong) {
         /*
          * Convert location a and b's lattitude and longitude from degrees to
          * radians
          */
         double aLatRad = aLat / DEGREES_TO_RADIANS;
         double aLongRad = aLong / DEGREES_TO_RADIANS;
         double bLatRad = bLat / DEGREES_TO_RADIANS;
         double bLongRad = bLong / DEGREES_TO_RADIANS;

         // Calculate the length of the arc that subtends point a and b
         double t1 = Math.cos(aLatRad) * Math.cos(aLongRad) * Math.cos(bLatRad)
                 * Math.cos(bLongRad);
         double t2 = Math.cos(aLatRad) * Math.sin(aLongRad) * Math.cos(bLatRad)
                 * Math.sin(bLongRad);
         double t3 = Math.sin(aLatRad) * Math.sin(bLatRad);
         double tt = Math.acos(t1 + t2 + t3);

         // Return a "naked" length for the calculated arc
         return tt;
     }

     /**
      * Calculates the distance between two addresses
      *
      * @param pointA
      *            GeoPoint of point A
      * @param pointB
      *            GeoPoint of point B
      * @param units
      *            Desired units
      * @return Distance between the two points in the desired units
      */
     public static double calculateDistance(GeoPoint pointA, GeoPoint pointB,
             int units) {
         return calclateArc(pointA.getLatitudeE6() / 1E6,
                 pointA.getLongitudeE6() / 1E6, pointB.getLatitudeE6() / 1E6,
                 pointB.getLongitudeE6() / 1E6) * EARTHS_RADIUS[units];
     }

     /**
      * Calculates the distance between two locations
      *
      * @param pointA
      *            Location of point A
      * @param pointB
      *            Location of point B
      * @param units
      *            Desired units
      * @return Distance between the two points in the desired units
      */
     public static double calculateDistance(Location pointA, Location pointB,
             int units) {
         return calclateArc(pointA.getLatitude(), pointA.getLongitude(),
                 pointB.getLatitude(), pointB.getLongitude())
                 * EARTHS_RADIUS[units];
     }
 }