Boundary Representation

• Models are a more explicit representation than CSG.
  
• The object is represented by a complicated data structure giving information about each of the object's faces, edges and vertices and how they are joined together.
  
• Appears to be a more natural representation for Vision since surface information is readily available.
  
• The description of the object can be into two parts:

Topology

-- records the connectivity of the faces, edges and vertices by means of pointers in the data structure.

Geometry

-- describes the exact shape and position of each of the edges, faces and vertices.

• The geometry of a vertex is just its position in space as given by its (x,y,z) coordinates.
  
• Edges may be straight lines, circular arcs, etc..
  
• A face is represented by some description of its surface (algebraic or parametric forms used).

 

Fig. 50 Faces, edges and vertices