1. A method for constructive modelling of articles, said method comprising the steps of: inputting into a data storage means scanning data relating to internal and/or external surfaces of an article; computing the stored scanning data according to a predetermined algorithm to reconstruct a plurality of parallel two dimensional cross-sectional images of the article; computing said plurality of two dimensional cross-sectional images according to a predetermined algorithm to generate a three dimensional co-ordinate data set for the article; and generating a three dimensional representation of said article by a constructive modelling process using selected sequential two dimensional image data sets computed from said three dimensional co-ordinate data set, said two dimensional image data sets being computed in parallel planes which are not parallel to the planes in which said two dimensional cross-sectional images are obtained by scanning.