A method determining a position of an animal part in an animal space in at least one direction, including: obtaining a two-dimensional image containing depth information； preprocessing the image according to first and second preprocessing modes, to provide respective first and second preprocessed images； comparing the first preprocessed image and the second preprocessed image to obtain at least one image difference； if the at least one image difference is below or equal to a respective predetermined threshold, processing the first preprocessed image according to a first position determining mode, and if the at least one image difference is above the predetermined threshold, processing the second preprocessed image according to a second position determining mode, to provide the position of the animal part. If a fast but not very accurate processing mode, and a slower but more accurate mode, are available, the method can suitably select one of these modes.
