计算两地间的距离

public static double computeDistance(double lat1, double lon1, double lat2, double lon2) {
     int MAXITERS = 20;
     lat1 *= Math.PI / 180.0;
     lat2 *= Math.PI / 180.0;
     lon1 *= Math.PI / 180.0;
     lon2 *= Math.PI / 180.0;

     double a = 6378137.0;
     double b = 6356752.3142;
     double f = (a - b) / a;
     double aSqMinusBSqOverBSq = (a * a - b * b) / (b * b);

     double L = lon2 - lon1;
     double A = 0.0;
     double U1 = Math.atan((1.0 - f) * Math.tan(lat1));
     double U2 = Math.atan((1.0 - f) * Math.tan(lat2));

     double cosU1 = Math.cos(U1);
     double cosU2 = Math.cos(U2);
     double sinU1 = Math.sin(U1);
     double sinU2 = Math.sin(U2);
     double cosU1cosU2 = cosU1 * cosU2;
     double sinU1sinU2 = sinU1 * sinU2;

     double sigma = 0.0;
     double deltaSigma = 0.0;
     double cosSqAlpha = 0.0;
     double cos2SM = 0.0;
     double cosSigma = 0.0;
     double sinSigma = 0.0;

     double cosLambda = 0.0;
     double sinLambda = 0.0;

     double lambda = L;
     for (int iter = 0; iter < MAXITERS; iter++) {
     double lambdaOrig = lambda;
     cosLambda = Math.cos(lambda);
     sinLambda = Math.sin(lambda);
    
     double t1 = cosU2 * sinLambda;
     double t2 = cosU1 * sinU2 - sinU1 * cosU2 * cosLambda;
     double sinSqSigma = t1 * t1 + t2 * t2;
    
     sinSigma = Math.sqrt(sinSqSigma);
     cosSigma = sinU1sinU2 + cosU1cosU2 * cosLambda;
     sigma = Math.atan2(sinSigma, cosSigma);
    
     double sinAlpha = (sinSigma == 0) ? 0.0 :
     cosU1cosU2 * sinLambda / sinSigma;
     cosSqAlpha = 1.0 - sinAlpha * sinAlpha;
    
     cos2SM = (cosSqAlpha == 0) ? 0.0 :
     cosSigma - 2.0 * sinU1sinU2 / cosSqAlpha;

     double uSquared = cosSqAlpha * aSqMinusBSqOverBSq;
     A = 1 + (uSquared / 16384.0) *
     (4096.0 + uSquared *(-768 + uSquared * (320.0 - 175.0 * uSquared)));
    
     double B = (uSquared / 1024.0) * 
     (256.0 + uSquared *(-128.0 + uSquared * (74.0 - 47.0 * uSquared)));