1. A method of obtaining a three-dimensional digital model of an artificial object, made up of a plurality of geometric primitives, the artificial object being in a single two-dimensional photograph or drawing, the method comprising: defining a two-dimensional outline of said artificial object within the photograph; interactively allowing a user to define cross-sectional profiles of successive ones of said geometric primitives, said cross-sectional profiles defining a third dimension; interactively allowing a user to provide sweep input to sweep respective defined cross-sectional profiles over an extent of a corresponding one of said geometric primitives within the image, said sweeping generating successive three-dimensional model primitives from existing detected edges of said corresponding geometric primitives and said sweeping of said respective profile; and aligning said plurality of three-dimensional model primitives to form said three-dimensional model.