计算距离算法googlemap

//private const double EARTH_RADIUS = 6378.137;   //地球半径

function rad(d){
	return d * Math.PI / 180.0;
}



function GetDistance( lat1,  lng1,  lat2,  lng2){ //p1纬度，p1经度，p2纬度,p2经度

var radLat1 = rad(lat1);

var radLat2 = rad(lat2);

var a = radLat1 - radLat2;

var  b = rad(lng1) - rad(lng2);

var s = 2 * Math.asin(Math.sqrt(Math.pow(Math.sin(a/2),2) +

Math.cos(radLat1)*Math.cos(radLat2)*Math.pow(Math.sin(b/2),2)));

s = s *6378.137 ;// EARTH_RADIUS;

s = Math.round(s * 10000) / 10000;

return s; //单位KM

}