Wire-frame Entities:

All the present CAD/CAM systems give users with fundamental wire-frame entities. Most wire-frame models consist of lines, points and arcs that are the fundamental entities of model. The entities might be divided into synthetic entities and analytical entities.

Analytical entities involve lines, points, arcs and circles, chamfers and fillets and conics such like parabola, ellipse and hyperbola. Several types of splines such like cubic spline, β and γ-splines , β-spline, and Bezier curves are synthetic entities. Entities are building blocks of geometric models therefore mathematical treatment of entities shall provide insight into CAD/CAM. Mathematical representation of these entities are provided in Table 1.

Table 1 : Methods of Defining Entities Defining Points

 (A) Absolute coordinate system point through its coordinates P (x, y, z).

 (B) Point through its polar coordinates.

 (c) Point like centre point of present entity. 

        P1 centre of line L                                          P2 centre of circle C           

 P3 centre of arc A

 Defining Lines

 (a) Line by two points

 (b) Parallel to or Perpendicular to an existing line

 L1 parallel to L 

L2 perpendicular to L

(c) Tangent to a provided circle and passing through a point

(d) Tangent to two given circles