This paper describes a system which converts a two-dimensional sketch with hidden lines removed of a single polyhedral object into a boundary representation solid model. The system improves on a previous system by Grimstead (1997) by analysing the sketch for symmetry elements and regularities. It uses the results of this analysis to produce a more plausible topological completion of the hidden parts of the object, and to enforce exact constraints on the geometry of the boundary-representation model.
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