Interpretation of engineering drawings of polyhedral and nonpolyhedral objects from orthographic projections

A system is presented for the interpretation of multiple-view engineering drawings. This system takes a set of two-dimensional orthographic projections and reconstructs the three-dimensional shape of the object, using a boundary representation model. Both polyhedral objects and objects with curved surfaces (spherical or cylindrical) can be interpreted. For its input, the system requires a set of two-dimensional lines as a description of the drawing to be interpreted. This type of description can be obtained from a system previously developed by Kasturi et al., which takes a paper-based drawing as input, recognizes 2D objects, and produces a list of lines contained in that drawing.; The system can accommodate auxiliary views in addition to the standard orthogonal views, and the layout of the views need not be known a priori. A tree representation is developed for describing the relationships between the views. A basis matrix formalism for relating the 2D view-based coordinates to the 3D object-based coordinates is also presented.; A general method is introduced which, unlike previous methods, avoids any assumptions about the nature of any nonplanar surfaces until a later stage of the process when more reliable decisions can be made. A new technique based on the Dempster-Shafer theory of evidence is introduced to guide the construction of the 3D model. This technique accommodates the additional complexity that results from deferring decisions about the object structure and also allows drawings with missing or omitted lines to be reasonably interpreted when information about the features they represent is available from other views. The system can also handle drawings with moderate errors in the alignment of the views and in the location of the input lines.