getCenterFromDegrees.php

<?php
/**
 * Get a center latitude,longitude from an array of like geopoints
 *
 * @param array data 2 dimensional array of latitudes and longitudes
 * For Example:
 * $data = array
 * (
 *   0 = > array(45.849382, 76.322333),
 *   1 = > array(45.843543, 75.324143),
 *   2 = > array(45.765744, 76.543223),
 *   3 = > array(45.784234, 74.542335)
 * );
*/


function GetCenterFromDegrees($data)
{
    if (!is_array($data)) return FALSE;

    $num_coords = count($data);

    $X = 0.0;
    $Y = 0.0;
    $Z = 0.0;

    foreach ($data as $coord)
    {
        $lat = $coord[0] * pi() / 180;
        $lon = $coord[1] * pi() / 180;

        $a = cos($lat) * cos($lon);
        $b = cos($lat) * sin($lon);
        $c = sin($lat);

        $X += $a;
        $Y += $b;
        $Z += $c;
    }

    $X /= $num_coords;
    $Y /= $num_coords;
    $Z /= $num_coords;

    $lon = atan2($Y, $X);
    $hyp = sqrt($X * $X + $Y * $Y);
    $lat = atan2($Z, $hyp);

    return array($lat * 180 / pi(), $lon * 180 / pi());
}
?>