PHP/MySQL: Select locations close to a given location from DB

Question

In PHP, I have the following code for calculating the distance between two locations:

<?php
function distance($lat1, $long1, $lat2, $long2) {
    // DEGREE TO RADIAN
    $latitude1 = $lat1/180*pi();
    $longitude1 = $long1/180*pi();
    $latitude2 = $lat2/180*pi();
    $longitude2 = $long2/180*pi();
    // FORMULA: e = ARCCOS ( SIN(Latitude1) * SIN(Latitude2) + COS(Latitude1) * COS(Latitude2) * COS(Longitude2-Longitude1) ) * EARTH_RADIUS
    $distance = acos(sin($latitude1)*sin($latitude2)+cos($latitude1)*cos($latitude2)*cos($longitude2-$longitude1))*6371;
    return $distance;
}
echo distance(9.9921962, 53.5534074, 9.1807688, 48.7771056); // Hamburg, DE - Stuttgart, DE
?>

But now, I want to select locations close to a given location via PHP from my MySQL database:

• The user enters his hometown
• My script gets the latitude/longitude values via the Google API
• In my database, I have about 200 locations with a field for the latitude value and a field for the longitude value
• I need a code for PHP and MySQL to select the 10 locations which are closest to the user's hometown

I hope you can help me. Thanks in advance!

Answer 1

MySQL Great Circle Distance (Haversine formula) does exactly what you need.

With only 200 records however you may as well just load them all and check them with code. The data set is really way too small to be worrying too much about database vs code or any other such optimizations.

Calculating distance between zip codes in PHP has a couple of PHP implementations of this algorithm.

Geo Proximity Search is pretty much the exact same problem you have.

Answer 2

Maybe something like

SELECT field1, field2, ...,
    ACOS(SIN(latitude / 180 * PI()) * SIN(:1) + COS(latitude / 180 * PI()) * COS(:2) * COS(:2 - longtidude)) * 6371 AS distance
    ORDER BY distance ASC;

or

SELECT field1, field2, ...,
    ACOS(SIN(RADIANS(latitude)) * SIN(:1) + COS(RADIANS(latitude)) * COS(:2) * COS(:2 - longtidude)) * 6371 AS distance
    ORDER BY distance ASC;

(directly translated from the PHP code)

:1 and :2 is $lat2/180*pi() and $long2/180*pi() respectively.