Digital cameras are often used on robots these days. One of the common limitations of these cameras is a relatively small Field of View. Consequently, the camera is usually tilted downwards in order to see the floor immediately in front of the robot. With the camera tilted, vertical edges no longer appear vertical in the image. This feature can however be used to advantage to discriminate amongst straight line edges extracted from the image when searching for landmarks. It might also be used to estimate angles of rotation and distances moved between successive images in order to assist with localisation.