$ll = '[{"lat":37.790388261934424,"lng":-122.46047996826172},{"lat":37.789608231530124,"lng":-122.46344112701416}]';
$ll = json_decode($ll);
print_r($ll);

打印...

Array
(
    [0] => stdClass Object
        (
            [lat] => 37.7903882619
            [lng] => -122.460479968
        )

    [1] => stdClass Object
        (
            [lat] => 37.7896082315
            [lng] => -122.463441127
        )

)