經緯度距離換算

 var EARTH_RADIUS = 6378137.0; //單位M
  var PI = Math.PI;

  function getRad(d) {
    return d * PI / 180.0;
  }
  function getDistance(lat1, lng1, lat2, lng2) {
    var f = getRad((lat1 + lat2) / 2);
    var g = getRad((lat1 - lat2) / 2);
    var l = getRad((lng1 - lng2) / 2);

    var sg = Math.sin(g);
    var sl = Math.sin(l);
    var sf = Math.sin(f);

    var s, c, w, r, d, h1, h2;
    var a = EARTH_RADIUS;
    var fl = 1 / 298.257;

    sg = sg * sg;
    sl = sl * sl;
    sf = sf * sf;

    s = sg * (1 - sl) + (1 - sf) * sl;
    c = (1 - sg) * (1 - sl) + sf * sl;

    w = Math.atan(Math.sqrt(s / c));
    r = Math.sqrt(s * c) / w;
    d = 2 * w * a;
    h1 = (3 * r - 1) / 2 / c;
    h2 = (3 * r + 1) / 2 / s;

    return d * (1 + fl * (h1 * sf * (1 - sg) - h2 * (1 - sf) * sg));
  }

  console.log('getDistance :', getDistance(30.2576800000,120.2047480000,30.2821940000,120.1178610000));
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