- 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).

- The geometry of a vertex is just its position in
space as given by its (

**Fig. 40 Faces, edges and vertices**

dave@cs.cf.ac.uk