twig - Symfony2: How to set the root path in a Symfony CLI command -

edit: cut short: there way call $kernel->getrootdir(); within twig extension? or maybe di container?

original question:

i try scale images on server using imagine. works fine log don't try trigger rendering via command line: in case looks there wrong path set- i'm getting error:

[twig_error_runtime]

an exception has been thrown during rendering of template ("file ../web/documents/4f59ef3f76e74_test3.jpg doesn't exist") in "....:detail.html.twig" @ line 72.

i'm using twig tag wrote myself:

 public function thumbnail($path,$width,$maxheight=0,$alt="",$absolute=false){          /* @var $imagine \imagine\gd\imagine */         $imagine = $this->container->get('imagine');          //$box = new \imagine\image\box($width, $height);          /* @var $image \imagine\image\imageinterface */         $image = $imagine->open("../web/".$path); ... 

i tried (both works when render template via browser request)

$image = $imagine->open($path); 

$path set "documents/4f59ef3f76e74_test3.jpg" "documents/" sub directory of "web"

any ideas?

ha- found it! retrieves absolute system file path of web folder:

$webroot = $this->container->get('kernel')->getrootdir()."/../web";