PHP Sorting nearest coordinates
mysql, php, sorting
Solution
Using Google's algorithm:
$lon = //your longitude
$lat = //your latitude
$miles = //your search radius
$query = "SELECT *,
( 3959 * acos( cos( radians('$lat') ) *
cos( radians( latitude ) ) *
cos( radians( longitude ) -
radians('$lon') ) +
sin( radians('$lat') ) *
sin( radians( latitude ) ) ) )
AS distance FROM yourtable HAVING distance < '$miles' ORDER BY distance ASC LIMIT 0, 5"
`latitude` and `longitude` in this query are going to be your lat/lon column names.
Problem
I have a MySQL table in a PHP webservice containing longitude and latitude. I want to send the user only the, let's say, 5 closest coordinates. I wrote the method which calculates a distance from coordinates to the ones the user sent in the POST request, but I'm not sure on how to sort it and only send back a few. Here is the distance method: ``` function distance($longToCompare,$latToCompare) { $dlong = $request_long - $longToCompare; $dlat = $request_lat - $latToCompare; $a = pow(sin($dlat/2)) + cos($latToCompare)*cos($request_lat)*pow(sin($dlong/2)); $c = 2*atan2(sqrt($a),sqrt(1-$a)); return 6373*$c; } ``` and the user currently gets the whole DB (for now, while developing it's small, but in the future it could be rather big) ``` $q = mysql_query("SELECT * FROM Coordinates"); $coordinates = array (); while ($e = mysql_fetch_assoc($q)) { $coordinates[] = $e; } print (json_encode($coordinates)); ``` Can anyone point me to the right direction? I'm rather new to PHP, I know I can create a custom sorting using uasort, but i'm not quite sure on how to use it using this distance function. EDIT: Using @Norse 's solution, the current query is: ``` $request_long = $_POST['longitude']; $request_lat = $_POST['latitude']; $km = 0.5; $query = "SELECT *, ( 6373 * acos( cos( radians('$request_lat') ) * cos( radians( latitude ) ) * cos( radians( longitude ) - radians('$request_long') ) + sin( radians('$request_lat') ) * sin( radians( latitude ) ) ) ) AS distance FROM Coordinates HAVING distance < '$km' ORDER BY distance ASC LIMIT 0, 5"; $coordinates = array (); while ($e = mysql_fetch_assoc($query)) { $coordinates[] = $e; } print (json_encode($coordinates)); ```