Calculate distance between two latitude and longitude in php using the Great-circle distance formulae

calculateDistance.php

<?php

function calculateDistance($firstLatitude, $firstLongitude, $secondLatitude,$secondLongitude)
{
    //get polar angle θ (theta) (angle with respect to polar axis)
    $theta = $firstLongitude - $secondLongitude;

    $radians = sin( 
                    deg2rad($firstLatitude)
                ) * sin(
                    deg2rad($secondLatitude)
                ) + cos(
                    deg2rad($firstLatitude)
                ) * cos(
                    deg2rad($secondLatitude)
                ) * cos(
                    deg2rad($theta)
                );

    //get the arc cosine value of given radians(distance in radians)
    $distance = acos($radians); 
    
    //convert radians into miles(multiple with earth radius in miles)
    $miles = $distance * 3959;
    
    //convert miles into kilometer(1 miles = 1.60934) 
    $km = $miles * 1.60934; 
    return $km;
}

$distance = calculateDistance(20.5937,78.9629,37.0902,95.7129);