**Chapter 1 - Modelling Basics**

**Part 3 - Polygons vs NURBS**

In this part you will learn what is a NURBS, what is it used for and what differences are between it and a polygon surface.

NURBS stands for Non-uniform rational B-spline. It is a mathematical model used in 3D applications to create curves and surfaces with a greater precision.

Let's first compare a NURBS curve with a curve made out of straight lines.

In this example, the yellow curve is a NURBS curve, while the black curve is made out of straight lines connected to each other via the red vertices.

For a even better representation, here is a NURBS circle vs one made out of straight lines.

Now let's take a look at some three dimensional objects and surfaces.

For the first comparison, let's look at a cylinder (tube).

The cylinder on the left is made out of NURBS, while the one on the right is made out of polygons (in this case, rectangles).

Here is the comparison between two spheres...

...and between a NURBS torus and a polygon torus.

Notice that the polygonal objects' shapes are not so well defined, since they are made out of polygons connected to each other. Of course, in order to define more rounded shapes, users have the ability to add extra levels of detail to their polygonal objects, as much as they want. The only downside is that the more polygons a shape contains the longer the rendering time will be, as the computer will have to calculate more surfaces.

Modelling NURBS surfaces has obvious advantages, but the process takes longer to get used to.

In part 4 we will actually start doing some standard modelling and learn how to create not only standard geometric objects, but also some more complex shapes.

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