计算地球上2点之间的距离

// 这个函数取2个坐标，一个起点坐标和一个终点坐标，并返回二者之间的距离（千米）
function computeDistance(startCoords,destCoords){
var startLatRads = degreesToRadians(startCoords.latitude);
var startLoingRads = degreesToRadians(startCoords.longitude);
var destLatRads = degreesToRadians(destCoords.latitude);
var destLongRads = degreesToRadians(destCoords.longitude);

var Radius = 6371; //radius of the Earth in km
var distance = Math.acos(Math.sin(startLatRads) * Math.sin(destLatRads) + Math.cos(startLatRads) * Math.cos(destLatRads) * Math.cos(startLoingRads - destLongRads)) * Radius;

return distance;
}

function degreesToRadians(degrees){
var radians = (degrees * Math.PI) / 180;
return radians;
}

// 测试
var startCoords = {
latitude: 29.8604472,
longitude:121.498982
};
var destCoords = {
latitude: 47.624851,
longitude:-122.52099
};

var km = computeDistance(startCoords,destCoords);
alert(km); //9293.980559898791