Calculate distance with variable lat and lon values

Hi

I have a problem with implementing variables into a function that calculate distance between 2 latitudes, longitudes.
One of them is constant, and the second one being passed from the form.

Here is the code:

$lon1 = $_POST['lon1'];
        $lat1 = $_POST['lat1'];
        $lon2 = '-0.30020239';
        $lat2 = '51.58734910';

function distance($lat11, $lon11, $lat22, $lon22) {
        $theta = $lon11 - $lon22;
        $dist = sin(deg2rad($lat11)) * sin(deg2rad($lat22)) +  cos(deg2rad($lat11)) * cos(deg2rad($lat22)) * cos(deg2rad($theta));
        $dist = acos($dist);
        $dist = rad2deg($dist);
        $miles = $dist * 60 * 1.1515;
                return $miles;
}

echo "
$lon1, $lat1<br>
$lon2, $lat2<br>";
//////////  return good calculation
echo distance(52.611644, -0.26304, 51.58734910, -0.30020239) . " miles<br>";

////////// my way - return wrong calculation
echo distance("$lon1", "$lat1", 51.58734910, -0.30020239) . " miles<br>";

As long as i have lat, lon values hardcoded is fine, but idea is to have this calculation done from variables.
Both will vary … tried different configurations … i’m losing it …

How should I code it ??

Thanks for your help in advance!

There was a problem in calling a distance() function. Function is defined as lat, lon, lat, lon, but i called it as lon, lat, lon, lat.

Being blind.

SOLVED.