Outline aid for a line digitiser

An outline aid 9 for a line digitiser 2 in which the aid 9 engages a digitiser arm 4 at a displaced location from an actual irregularly shaped body 1 such that irregularities in that shape do not prevent the digitiser 2 identifying and producing a desired plan outline of the irregular body 1. The aid 9 is for particular use in relation to determining a footprint outline of a human foot in order to create orthopaedic shoes. The outline aid 9 is preferably a cylindrical body arranged to slide upon a surface upon which an irregular body is located and having an upper engagement surface 11 to engage a digitiser arm 4. This slidable surface 10 and engagement surface 11 being separated by a side wall of sufficient height to ensure that the aid always engages the surface of the desired outline of the body.