1. A method comprising: in a portable device, receiving identification data sensed from a passive chip device associated with an object; and by reference to said identification data, obtaining a previously-established second set of data; wherein the second set of data comprises salient points, said salient points comprising, for each of plural salient points: location information for said point on the object; and orientation information for said point on the object, and/or information representing a feature vector associated with said location.