因为地球是个球形的，所以根据两地的经纬度是可以计算出距离的。原理就不多说了。直接上代码吧。

swift版本：

static func calculateLineDistance(var0:LonLat, var1:LonLat) -> Double {
        let DEG_TO_RAD:Double = 0.0174532925199432958
        var var2 = Double(var0.lon!);
        var var4 = Double(var0.lat!);
        var var6 = Double(var1.lon!);
        var var8 = Double(var1.lat!);
        var2 = DEG_TO_RAD * var2!;
        var4 = DEG_TO_RAD * var4!;
        var6 = DEG_TO_RAD * var6!;
        var8 = DEG_TO_RAD * var8!;
        let var10 = sin(var2!);
        let var12 = sin(var4!);
        let var14 = cos(var2!);
        let var16 = cos(var4!);
        let var18 = sin(var6!);
        let var20 = sin(var8!);
        let var22 = cos(var6!);
        let var24 = cos(var8!);
        var var28 = Array<Double>()
        var var29 = Array<Double>()
        var28.append(var16 * var14)
        var28.append(var16 * var10)
        var28.append(var12)
        var29.append(var24 * var22)
        var29.append(var24 * var18)
        var29.append(var20)
        return (asin(sqrt((var28[0] - var29[0]) * (var28[0] - var29[0]) + (var28[1] - var29[1]) * (var28[1] - var29[1]) + (var28[2] - var29[2]) * (var28[2] - var29[2])) / 2.0) * 1.27420015798544E7)
    }

Dart版本：

  static const double DEG_TO_RAD = 0.0174532925199432958;

  static double calculateLineDistance(LatLng var0, LatLng var1) {
    if(var0 != null && var1 != null){
      double var2 = var0.longitude;
      double var4 = var0.latitude;
      double var6 = var1.longitude;
      double var8 = var1.latitude;
      var2 *= DEG_TO_RAD;
      var4 *= DEG_TO_RAD;
      var6 *= DEG_TO_RAD;
      var8 *= DEG_TO_RAD;
      double var10 = sin(var2);
      double var12 = sin(var4);
      double var14 = cos(var2);
      double var16 =cos(var4);
      double var18 = sin(var6);
      double var20 = sin(var8);
      double var22 = cos(var6);
      double var24 = cos(var8);
      List<double> var28 = List<double>(3);
      List<double> var29 = List<double>(3);
      var28[0] = var16 * var14;
      var28[1] = var16 * var10;
      var28[2] = var12;
      var29[0] = var24 * var22;
      var29[1] = var24 * var18;
      var29[2] = var20;
      return (asin(sqrt((var28[0] - var29[0]) * (var28[0] - var29[0]) + (var28[1] - var29[1]) * (var28[1] - var29[1]) + (var28[2] - var29[2]) * (var28[2] - var29[2])) / 2.0) * 1.27420015798544E7);
    }else{
      return 0.0;
    }
  }

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