6.1 INTRODUCTION

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When we have a basic shape we can use equations to describe the shape,

- circle

- sphere

- oval

- plane

- line

- conic

- etc.

When the shape is not common, splines enable curved surfaces to be defined easily, with good control of the shape

The source of control points for the splines are experimental data or design parameters or artistic judgement, etc.

A spline uses end points, and some internal control points to adjust the shape which could not be defined with known primitive geometries.

Common spline types are,

- Polynomial

- B-Spline

- Bezier Splines

- Hermite Splines

- Catmull-Ron

- etc.

A spline can be used as a face in a B-Rep (solid) model.

Some splines allow variable tension, such as the Catmull-Ron, and some B-Splines. This allows a skin which is stretched, tightly, or loose.

Mathematical functions for curves and surfaces may be explicit or parametric.

Explicit - The values are directly related

Parametric - The curve is described by varying other numbers