Calculate proximity in php

Question

I am trying to write a php function that calculates proximity between two points but I cant get it to work.

I am currently using a function found here: http://www.zipcodeworld.com/samples/distance.php.html

function distance($lat1, $lon1, $lat2, $lon2, $unit) { 

$theta = $lon1 - $lon2; 
$dist = sin(deg2rad($lat1)) * sin(deg2rad($lat2)) +  cos(deg2rad($lat1)) * cos(deg2rad($lat2)) * cos(deg2rad($theta)); 
$dist = acos($dist); 
$dist = rad2deg($dist); 
$miles = $dist * 60 * 1.1515;
$unit = strtoupper($unit);

if ($unit == "m") {
    return ($miles * 1.609344)/1000; 
} 
else if ($unit == "N") {
  return ($miles * 0.8684);
} 
else {
    return $miles;
  }
}

---

My application requires precision down to meters but no matter what I do I dont get correct results.

I get the coordinates from here: http://itouchmap.com/latlong.html

What am I doing wrong? Can you please help me out with this?

Thanks

Mike

Answer 1

I wrote this little class a while ago now, but it should help you with better distance calculations than the method in your question: https://github.com/treffynnon/Geographic-Calculations-in-PHP

To complete your question with the above link would be:

$Geography = new Geography();
echo $Geography->getDistance($lat1, $lon1, $lat2, $lon2);

Will give the distance in metres using Vincenty's formulae for the distance calculation.

The Vincenty's formulae used in my class is a PHP port of the javascript function available at http://www.movable-type.co.uk/scripts/LatLongVincenty.html

Answer 2

Here's a page with great detail on the algorithms available with JS examples: http://www.movable-type.co.uk/scripts/latlong.html