A controller for a movable unloading apparatus of an agricultural harvesting machine, wherein the movable unloading apparatus directs crop material from the agricultural harvesting machine to a container driven in the vicinity of the agricultural harvesting machine, and wherein the controller receives image data representative of a stream of crop material as it passes from the unloading apparatus to the container; processes the image data in order to determine a shape of the stream of crop material in the image data; and sets an attribute of the unloading apparatus in accordance with the determined shape of the stream of crop material in order to direct the crop material from the unloading apparatus to the container.