$x_pi = 3.14159265358979324 * 3000.0 / 180.0;

//火星坐标系 (GCJ-02)转百度坐标系 (BD-09)算法
function bd_encrypt($gg_lat, $gg_lon)
{
global $x_pi;
$x = $gg_lon;
$y = $gg_lat;
$z = sqrt($x * $x + $y * $y) + 0.00002 * sin($y * $x_pi);
$theta = atan2($y, $x) + 0.000003 * cos($x * $x_pi);
$bd_lon = $z * cos($theta) + 0.0065;
$bd_lat = $z * sin($theta) + 0.006;

}

//百度坐标系 (BD-09) 转火星坐标系 (GCJ-02) 算法
function bd_decrypt($bd_lat, $bd_lon)
{
global $x_pi;
$x = $bd_lon - 0.0065;
$y = $bd_lat - 0.006;
$z = sqrt($x * $x + $y * $y) - 0.00002 * sin($y * $x_pi);
$theta = atan2($y, $x) - 0.000003 * cos($x * $x_pi);
$gg_lon = $z * cos($theta);
$gg_lat = $z * sin($theta);

}

转自：http://blog.csdn.net/coolypf/article/details/8569813

http://segmentfault.com/a/1190000000498434