Symmetry Plane Detection for 3D CAD Volumes

Symmetry properties of components have many applications during a product development process, including shape transformations for modification purposes, Finite Element Analysis (FEA), model retrieval, etc. This paper presents an algorithm to generate 3D model symmetry planes using the B-Rep model of CAD volumes. In the framework of CAD software, 3D models are described as B-Rep volume models. Design processes of volume models strongly rely on extrusion and revolution primitives from sketches containing essentially straight line segments and circular arcs. Hence, the boundary surfaces considered are planes, cylinders, cones, tori and spheres. The object boundary is effectively processed as an infinite set of points. Global symmetry properties of faces are derived to initiate the global symmetry planes of the object. To this end, the intersection curves between two adjacent faces are used to characterize possible global symmetry planes of the object. Then, the algorithm starts analyzing the symmetry properties of couple of faces. Subsequently, the candidate symmetry planes set up contains all the possible global symmetry planes. Finally, the symmetry properties of neighboring faces help determining robustly the global symmetry planes, whether there is a finite number or an infinite number.