Solid reconstruction from orthographic views using 2-stage extrusion

In this paper, a method called 2-stage extrusion is proposed to reconstruct a solid by modifying the incremental extrusion for translucent object domain. The algorithm has two extrusion stages. In each stage, geometric entities from only three orthogonal views (viz. top, front and right) are used. The entities involve both solid and dashed lines in each view. In the first stage, an exterior contour region in each view is swept along its normal direction according to the corresponding object dimension. As a result, three extrusion-solids are produced. Intersection of the three extrusion-solids forms a basic-solid. Next, all interior entities of each view are treated by a filtering process. If all interior entities are discarded in the filtering, the second stage will be skipped and the basic-solid becomes a solution-solid. On the other hand, if any interior entity remains after filtering, they are processed in the second stage to generate an excess-solid. In this case, the basic-solid subtracts the excess-solid to form the final three-dimensional solution-solid.