1. A method of target recognition comprising the steps of: providing a set of 3D data corresponding to a reference object; obtaining a set of 3D data corresponding to a target object; deriving a translation invariant 3D signatures for each of the 3D data sets comparing the translation invariant 3D signatures for the reference object and the target object to derive an estimate of the orientation of the target with respect to the reference data; bringing the target data and reference data into rotational alignment according to said derived estimate of orientation; and comparing the aligned target data with the reference data and deriving a measure of similarity based on said comparison.