Approximating smooth surfaces with Polygon nets

Networks of polygons are used to represent smooth surfaces. They are, of course, only an approximation to the true surface, but they are adequate for most computer graphics tasks. One of the commonest uses of the technique is to approximate a cylinder by the use of a set of flat polygons.

The Lambert shading model is a great improvement over wire-frame drawings as far as realism is concerned. It is also a reasonably fast technique when compared to some of the alternatives that we are about to meet. It is, however, far from perfect. Using a different colour for each polygon means that the polygons show up very clearly (the appearance of the model is said to be faceted). This is fine for a cube, but not so good when attempting to use the polygon as part of a smooth surface. Figure 3.22 shows 32 flat surfaces, arranged in a circle, pretending to be a cylinder. The difference in intensity between neighbouring sections can easily be seen.