Abstract: The method comprising attaching a 3D sensor (20) on a top part of the container (10) in a position (P) and with an orientation (O) such that its field of view (FOV) is oriented towards the content (11) stored in the container (10); acquiring, by the 3D sensor (20), a depth map (DM); and computing, by a computing unit, a 3D surface model by processing said acquired depth map (DM) and using said given position (P), orientation (O) and field of view (FOV), and a 3D level model by removing from the computed 3D surface model the points corresponding to the interior walls of the container (10), using a 3D function that searches the intersection or matching between the 3D surface model and the shape of the container (S), and filling in the missing points corresponding to the content (11) that falls out of the field of view (FOV) of the 3D sensor (20).