3-D models are often created using the same basic techniques.
There are many approaches to 3-D modeling and many software programs to facilitate the process. However, whatever the purpose of a 3-D model, there are a set of basic techniques that tend to be used, both individually and when combined to create a more comprehensive approach. Although the underlying implementation of 3-D design generally uses complex mathematical functions, most programs allow users to carry out the modeling process without mathematical experience.
Primitive modeling uses basic geometric shapes and combines them to construct more complex structures. The underlying representation of primitive elements is based on mathematical functions and definitions, which makes them extremely accurate and reliable as components in larger models. Typically, primitives will feature in 3-D modeling projects that involve technical structures, for example those used in engineering contexts. 3-D modeling software programs usually automate the use of primitive elements so that no explicit knowledge of the mathematical aspects is necessary.
Polygonal modeling is a versatile technique that can be used within a variety of contexts. The building blocks of a polygonal element in a 3-D model include lines that connect vertexes, which in turn are defined points in space. Three lines connecting three points would be a simple example of a polygon in 3-D space. The modeling process involves the combining, dividing and extrusion of these polygons to create a structural model. An advantage to using polygonal techniques is that computer programs are generally able to render them effectively and fast. A disadvantage to polygonal modeling is that curves cannot be accurately represented.
Non-Uniform Rational B-Spline modeling, or NURBS, uses curves defined through mathematical functions. Most modeling software programs automate NURBS techniques so that mathematical expertise is unnecessary. The splines (for drawing curves) within NURBS modeling can typically be controlled easily and manipulated through software, and their structures are influenced by control points that are weighted, drawing the curves in particular directions. One of the primary advantages to using NURBS is that smooth curves can be achieved.
Subdivision modeling involves techniques that are applied to an already existing model and has some of the features of both polygonal and NURBS modeling. An existing polygonal model may have alterations performed on it through subdivision techniques, such as dividing polygonal elements into further polygons, creating a smoother structure. The addition of further control points and vertexes gives a greater level of control over a structure through subdivision. Subdivision techniques are an example of 3-D modeling combining different approaches to achieve the detail and structure required by any particular project.