获取经纬指定距离的四个点

    var EARTH_RADIUS = 6378137.0;//地球赤道半径(单位：m。6378137m是1980年的标准，比1975年的标准6378140少3m）

/// <summary>
/// 弧度转换为角度数公式
/// </summary>
/// <param name="d"></param>
/// <returns></returns>
function degrees(d) {
    return d * (180 / Math.PI);
}

/// <summary>
/// 以一个经纬度为中心计算出四个顶点
/// </summary>
/// <param name="Degree1">中心点</param>
/// <param name="distance">半径(米)</param>
/// <returns></returns>
function GetDegreeCoordinates(Degree1, distance) {
    var dlng = 2 * Math.asin(Math.sin(distance / (2 * EARTH_RADIUS)) / Math.cos(Degree1.X));
    dlng = degrees(dlng);//一定转换成角度数
    var dlat = distance / EARTH_RADIUS;
    dlat = degrees(dlat);//一定转换成角度数
    let data = [
            [xx(Degree1.X + dlng), xx(Degree1.Y + dlat)],//right-top
        [xx(Degree1.X - dlng), xx(Degree1.Y + dlat)],//left-top
        [xx(Degree1.X - dlng), xx(Degree1.Y - dlat)],//left-bottom
        [xx(Degree1.X + dlng), xx(Degree1.Y - dlat)]] //right-bottom
    return data;
}

function xx(num){
    num = num.toString();
    let xxx = num.split(".");
    xxx[1] = xxx[1].substr(0,6);
    
    return xxx[0]+'.'+xxx[1];
 }