How to calculate distance from lat/long in php?

i would not recommend dumping distance calculations in your sql statement, even though i admit that the solution presented by 'denil' is ingenious.

there are 3 downsides: code maintenance, sql server overload AND (above all) the earth is not symmetrical (it is like an old dented baseball that was run over by a truck). this means that you might want to change the code in the future (there are some VERY sophisticated algorithms out there - http://en.wikipedia.org/wiki/Geographical_distance).

i recommend using a separate function that calculates distance with a simple common algorithm (similar if not identical to denil's). i submit this code which is pure php (no need to use googlemaps api):

<?phpfunction distanceGeoPoints ($lat1, $lng1, $lat2, $lng2) {    $earthRadius = 3958.75;    $dLat = deg2rad($lat2-$lat1);    $dLng = deg2rad($lng2-$lng1);    $a = sin($dLat/2) * sin($dLat/2) +       cos(deg2rad($lat1)) * cos(deg2rad($lat2)) *       sin($dLng/2) * sin($dLng/2);    $c = 2 * atan2(sqrt($a), sqrt(1-$a));    $dist = $earthRadius * $c;    // from miles    $meterConversion = 1609;    $geopointDistance = $dist * $meterConversion;    return $geopointDistance;}// YOUR CODE HEREecho distanceGeoPoints(22,50,22.1,50.1);?>

there are a number of free softwares (try gps trackmaker) that will allow you to check the margin of error for your part of the globe (if you need precision). for the above lat/long pair, the error is within +/- 0.1% (according to local topographers).

ATTENTION: this formula gives you CARTOGRAPHIC distance (distance at sea level), not TOPOGRAPHIC distance (disconsiders topography).

I did this a few weeks ago.

This link is your best bet:

http://code.google.com/apis/maps/articles/phpsqlsearch.html

Even if you don't use their API, their PHP and SQL query helped really well.

Try this query. I found this one when googling but forgot who created it

SELECT a.*,            3956 * 2 * ASIN(SQRT( POWER(SIN(($lat - lat) * pi()/180 / 2), 2) + COS($lat * pi()/180) * COS(lat * pi()/180) *            POWER(SIN(($long - longi) * pi()/180 / 2), 2) )) as            distance FROM table            GROUP BY id HAVING distance <= 500 ORDER by distance ASC

$lat and $long variable is the current position of user. lat and longi is the latitude and longitudle of entries