Wire-frame Entities:

All the existing CAD/CAM systems provide users with basic wire-frame entities. Mostly wire-frame models consist of points, arcs and lines, which are the basic entities of model. The entities may be divided into analytical entities and synthetic entities.

Analytical entities involved points, arcs, lines and circles, fillets and chamfers and conics such like ellipse, parabola and hyperbola. Several types of splines such like, β-spline, cubic spline β & γ-splines and Bezier curves are synthetic entities. Entities are building blocks of geometric models therefore mathematical treatment of entities would provide insight in CAD/CAM.

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

(2) Point by its polar coordinates.

 (3) Point as centre point of an existing entity.          A

P₁ centre of line L                              P₂ centre of circle C                           P₃ centre of arc A