The Cararra Studio. Chapter 1: 3D Modeling Concepts and Techniques | 3 | WebReference

# The Cararra Studio. Chapter 1: 3D Modeling Concepts and Techniques | 3

### Subdivision Surfaces

Polygonal modeling is the basis for most 3D modeling. Sometimes, though, polygonal models with low polygon counts can look rough around the edges. Adding more polygons in an attempt to smooth the model can be cumbersome because it makes the model difficult to edit and takes up computer memory.

Modeling with subdivision surfacesallows you to keep the basic number of polygons low yet achieve a visually smooth model (Figure 1.11a). Subdivision surfaces work by calculating the positions of neighboring polygons in the original model and smoothing the surface by dynamically subdividing the polygons, as seen in Figure 1.11b.

 FIGURE 1.11 Subdivision surfaces make a low polygon count model (a) appear smooth (b). FIGURE 1.12 Geometric primitives.

Chapter 10, “Organic Modeling with the Vertex Modeler,” covers using subdivision surfaces to model a human head.

### Primitives

Geometric primitives are 3D objects that are defined by mathematical formulas and cannot be broken down into parts, although they can be altered with deformers. Carrara Studio provides six geometric primitive shapes: sphere, cube, cone, plane, cylinder, and icosahedra (see Figure 1.12). Because primitives are defined instead of constructed, they use much less computer resources. This efficiency makes them ideal for building complex shapes.

### Surface Types

There are three basic surface types: loft, lathe, and extrusion.

### Loft

Loftingis a term borrowed from shipbuilding. Ships and boats are usually constructed from cross sections that are then lofted or skinned with wooden planks (or as in the case of today’s ships, metal or fiberglass resins) to create the hull of a ship. In 3D, lofting creates surfaces by skinning polylines or curves (see Figure 1.13).

FIGURE 1.13 Lofting, an old shipbuilding term, is used in 3D to create surfaces by connecting cross sections.

In the real world, a lathe is a tool that turns a block of wood at a high speed and allows a carpenter to evenly carve intricate shapes and designs into the wood, like banisters or table legs. The 3D lathe tool works much the same way, allowing a 3D artist to take a profile and sweep it (turn it) around an axis or curve to quickly create complex surfaces, as in Figure 1.14.

FIGURE 1.14 Lathing was used to take a polygon and create a complex shape.

### Extrusion

The extrusion function is the most basic tool in 3D, and the most common method used to build models. Polygonal extrusion simply takes a face or set of faces and moves them out from their original position; in this way, new polygons and surfaces are created along the extrusion path. In the Carrara Studio Spline modeler, extrusion takes a cross section and extrudes it along a spline curve to create 3D surfaces (see Figure 1.15).

FIGURE 1.15 Face extrusion (a), single rail extrusion (b), and extrusion along a curve (c).

### Modeling with Curves

As discussed earlier, one of the properties of a polygon is that it is rigid and by itself cannot form curves. Luckily, curves come to the rescue. A curveis a mathematical object that is defined by points and the lines that connect those points. The lines might be straight as in the case of a linear curve, or round as with Bézier curves. There are many more types of curves, but these are the ones that Carrara Studio uses in the Spline modeler, so we will focus on these.

Linear curves can look like polygonal lines (polylines), but the mathematics behind linear curves is more complex, giving them more flexibility. Linear curves are used to create creases and corners in models built using the Spline modeler as seen in Figure 1.16.

Bézier curves are powerful tools that can help build almost any 3D shape. The path of a Bézier curve is determined by edit points and the lines between the edit points. The edit points in a Bézier curve contain control handles that allow fine control over the curvature or arch of the connecting line. Bézier curves can be used to easily create smooth shapes or smooth transitions between shapes (see Figure 1.17).

FIGURE 1.16 Linear curves are used to create corners and creases.

FIGURE 1.17 Bézier curves create smooth shapes and transitions.

### Summary

In this chapter, we introduced some of the basic concepts behind building 3D models. Although learning the basics in 3D might not seem as glamorous as diving right in and building cool 3D models and creating animations, it is an important step in becoming a well-rounded 3D artist. In the next chapter, we will learn some of the basic concepts in texturing 3D models.

Created: March 27, 2003
Revised: February 13, 2003

URL: http://webreference.com/3d/cararra/1