getting distance between two point using Haversine_formula

Question

Here is my code, It gives result .

I have used co-ordinate points for Ahmedabad , Banglore. Distance diff should be near to 1500 but here I get 32200

function points{
      $lat_a = 12.96;
        $lon_a = 77.56;
        $lat_b = 23.03;
        $lon_b = 72.58;
        $earth_radius = 6372.795477598;
      $delta_lat = $lat_b - $lat_a ;
      $delta_lon = $lon_b - $lon_a ;
      $a = pow(sin($delta_lat/2), 2);
      $a += cos(deg2rad($lat_a)) * cos(deg2rad($lat_b)) * pow(sin(deg2rad($delta_lon/29)), 2);
      $c = 2 * atan2(sqrt($a), sqrt(1-$a));
      $distance = 2 * $earth_radius * $c;
      $distance = round($distance, 4);
        echo "<br/>dist $distance";
}

Answer 1

$lat_a = 12.96;
$lon_a = 77.56;
$lat_b = 23.03;
$lon_b = 72.58;

$earth_radius = 6372.795477598;

$delta_lat = $lat_b - $lat_a ;
$delta_lon = $lon_b - $lon_a ;

$a = pow(sin(deg2rad($delta_lat/2)), 2) + cos(deg2rad($lat_a)) * cos(deg2rad($lat_b)) * pow(sin(deg2rad($delta_lon/2)), 2);
$c = 2 * asin(sqrt($a));
$distance = $earth_radius * $c;
$distance = round($distance, 4);

echo "<br/>dist $distance"; // dist 1237.3685

Answer 2

$a = pow(sin($delta_lat/2), 2); 

That is still in degrees, so you should use

$a = pow(sin(deg2rad($delta_lat)/2), 2); 

Instead.

Answer 3

Below is the Haversine formulae as a PHP function. I keep a version of it online for download:

http://www.opengeocode.org/download/haversine/haversine.php.txt

If you want miles, change 6372.8 to 3959. Also, you can find a lot of discussion on distant calculation on the closed question: MySQL Great Circle Distance (Haversine formula)

<?php
// Get Distance between two lat/lng points using the Haversine function
// First published by Roger Sinnott in Sky & Telescope magazine in 1984 (“Virtues of the Haversine”)
//
function Haversine( $lat1, $lon1, $lat2, $lon2) 
{
    $R = 6372.8;    // Radius of the Earth in Km

    // Convert degress to radians and get the distance between the latitude and longitude pairs
    $dLat = deg2rad($lat2 - $lat1);
    $dLon = deg2rad($lon2 - $lon1);

    // Calculate the angle between the points
    $a = sin($dLat/2) * sin($dLat/2) + cos(deg2rad($lat1)) * cos(deg2rad($lat2)) * sin($dLon/2) * sin($dLon/2);
    $c = 2 * asin(sqrt($a));
    $d = $R * $c;

    // Distance in Kilometers
    return $d;
}
?>