gistfile1.php

<?php
function intersectPoint($line1start, $line1end, $line2start, $line2end)
{
    $x1 = (double) $line1start['lat'];
    $y1 = (double) $line1start['lng'];
    $x2 = (double) $line1end['lat'];
    $y2 = (double) $line1end['lng'];
    $x3 = (double) $line2start['lat'];
    $y3 = (double) $line2start['lng'];
    $x4 = (double) $line2end['lat'];
    $y4 = (double) $line2end['lng'];

    $div = (($y4 - $y3) * ($x2 - $x1)) - (($x4 - $x3) *($y2 - $y1));
    if(!$div) return null;
    $ua = ((($x4 - $x3) * ($y1 - $y3)) - (($y4 - $y3) * ($x1 - $x3))) / $div;
    $ub = ((($x2 - $x1) * ($y1 - $y3)) - (($y2 - $y1) * ($x1 - $x3))) / $div;
    if($ua >= 0 && $ua <= 1 && $ub >= 0 && $ub <= 1)
    {
        AppCommUtility::echof("ua $ua ub $ub div $div");
        return array(
            'lat' => $x1 + ($ua * ($x2 - $x1)),
            'lng' => $y1 + ($ua * ($y2 - $y1))
        );
    }
    return null;
}