**3.3.1 Boundary representation**

Based on segmented regions (with fitted surfaces), a region adjacent graph is built. This graph reflects the complete topology and serves as the basis for building the final B-rep model, also called stitched models, where the individual bounded surfaces are glued together along their common edges to form an air-tight surface model.

In general, there are three steps involved in constructing B-rep models, flattening, edges and vertices calculations, and stitching (Várady et al., 1998). In flattening step, regions are extended outwards until all triangles have been classified. Note that this step is necessary to remove all gaps between regions. Sharp edges can be calculated using surface-surface intersection routines, and vertices where three surfaces meet are also determined. During the process, a complete B-rep topology tree is also constructed. A B-rep model can then be created by stitching together the faces, edges, and vertices. This operation is commonly supported by most solid modeling kernels.
