Preprocessing of engineering drawings for 3D reconstruction

The necessity of a preprocessing step which should precede the application of any 3-D reconstruction algorithm from a set of views provided by any manually or automatically prepared engineering machine drawing is discussed as a task of a machine drawing understanding system (MDUS). The essence of this preprocessing step is the distinction between, and separation of, geometry and annotation entities. Since the core of annotation is dimensioning, a graph-theoretic approach to the analysis of dimensioning of a restricted class of engineering machine drawings that describe two-and-one-half-dimensional objects represented by normalons is introduced. Drafting standards require that the induced dimensioning graph of a properly dimensioned normalon be a tree, as proved by the normalon proper dimensioning theorem. The theorem provides the theoretical basis for a MDUS view-level phase that assesses the completeness of the set of dimension sets detected individually in a previous, syntax-based dimension-set-level phase