A method for constructive modelling of articles including prostheses and anatomical pathology wherein CT scan data is computed to construct a plurality of two dimensional cross sectional images along one axis and the two dimensional image data is computed to create three dimensional coordinate data sets for the articles to be modelled. The three dimensional data sets are then computed to obtained spaced parallel two dimensional image data sets in a second plane of the article and the reconstructed two dimensional image data sets are employed in a constructive modelling process to produce a three dimensional model of the article or part thereof.