计算距离的逻辑是从Android的提供的接口（Location.distanceBetween）中拔来的，应该是最精确的方法了

php代码

<?php
function computeDistance($lat1, $lon1,
             $lat2, $lon2) {
             // using the "Inverse Formula" (section 4)

             $MAXITERS = 20;
             // Convert lat/long to radians
             $lat1 *= pi() / 180.0;
             $lat2 *= pi() / 180.0;
             $lon1 *= pi() / 180.0;
             $lon2 *= pi() / 180.0;

             $a = 6378137.0; // WGS84 major axis
             $b = 6356752.3142; // WGS84 semi-major axis
             $f = ($a - $b) / $a;
             $aSqMinusBSqOverBSq = ($a * $a - $b * $b) / ($b * $b);

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

             $cosU1 = cos($U1);
             $cosU2 = cos($U2);
             $sinU1 = sin($U1);
             $sinU2 = sin($U2);
             $cosU1cosU2 = $cosU1 * $cosU2;
             $sinU1sinU2 = $sinU1 * $sinU2;

             $sigma = 0.0;
             $deltaSigma = 0.0;
             $cosSqAlpha = 0.0;
             $cos2SM = 0.0;
             $cosSigma = 0.0;
             $sinSigma = 0.0;
             $cosLambda = 0.0;
             $sinLambda = 0.0;

             $lambda = $L; // initial guess
             for ($iter = 0; $iter < $MAXITERS; $iter++) {
                 $lambdaOrig = $lambda;
                 $cosLambda = cos($lambda);
                 $sinLambda = sin($lambda);
                 $t1 = $cosU2 * $sinLambda;
                 $t2 = $cosU1 * $sinU2 - $sinU1 * $cosU2 * $cosLambda;
                 $sinSqSigma = $t1 * $t1 + $t2 * $t2; // (14)
                 $sinSigma = sqrt($sinSqSigma);
                 $cosSigma = $sinU1sinU2 + $cosU1cosU2 * $cosLambda; // (15)
                 $sigma = atan2($sinSigma, $cosSigma); // (16)
                 $sinAlpha = ($sinSigma == 0) ? 0.0 :
                     $cosU1cosU2 * $sinLambda / $sinSigma; // (17)
                 $cosSqAlpha = 1.0 - $sinAlpha * $sinAlpha;
                 $cos2SM = ($cosSqAlpha == 0) ? 0.0 :
                     $cosSigma - 2.0 * $sinU1sinU2 / $cosSqAlpha; // (18)

                 $uSquared = $cosSqAlpha * $aSqMinusBSqOverBSq; // defn
                 $A = 1 + ($uSquared / 16384.0) * // (3)
                     (4096.0 + $uSquared *
                      (-768 + $uSquared * (320.0 - 175.0 * $uSquared)));
                 $B = ($uSquared / 1024.0) * // (4)
                     (256.0 + $uSquared *
                      (-128.0 + $uSquared * (74.0 - 47.0 * $uSquared)));
                 $C = ($f / 16.0) *
                     $cosSqAlpha *
                     (4.0 + $f * (4.0 - 3.0 * $cosSqAlpha)); // (10)
                 $cos2SMSq = $cos2SM * $cos2SM;
                 $deltaSigma = $B * $sinSigma * // (6)
                     ($cos2SM + ($B / 4.0) *
                      ($cosSigma * (-1.0 + 2.0 * $cos2SMSq) -
                       ($B / 6.0) * $cos2SM *
                       (-3.0 + 4.0 * $sinSigma * $sinSigma) *
                       (-3.0 + 4.0 * $cos2SMSq)));

                 $lambda = $L +
                     (1.0 - $C) * $f * $sinAlpha *
                     ($sigma + $C * $sinSigma *
                      ($cos2SM + $C * $cosSigma *
                       (-1.0 + 2.0 * $cos2SM * $cos2SM))); // (11)

                 $delta = ($lambda - $lambdaOrig) / $lambda;
                 if (abs($delta) < 1.0e-12) {
                     break;
                 }
             }

             return  $b * $A * ($sigma - $deltaSigma);
}
echo computeDistance(34.8082342, 113.6125439, 34.8002478, 113.659779);
?>