Every object, character, and environment in every computer-animated movie or 3D video game is comprised of 3D models. In this guide, we break down the major components of a 3D model, explaining faces, edges, vertices, and more.
What Is a 3D Model?
A 3D Model is a mathematical representation of any three-dimensional object (real or imagined) in a 3D software environment. Unlike a 2D image, 3D models can be viewed in specialized software suites from any angle, where they can be scaled, rotated, or freely modified.
Types of 3D Models
Two primary types of 3D models are used in the film and games industry. The most apparent difference between them is the way they’re created and manipulated (there are differences in the underlying math as well, but that’s less important to the end-user).
NURBS Surface
A non-uniform rational B-spline, or NURBS, is a smooth surface model created through the use of Bezier curves (think of it as a 3D version of the MS Paint pen tool). To form a NURBS surface, the artist draws two or more curves in a 3D space, which are manipulated by moving handles called control vertices (CVs) along the x-, y-, or z-axis. The software application interpolates the space between curves and creates a smooth mesh between them. NURBS surfaces have the highest level of mathematical precision and are most commonly used in modeling for engineering and automotive design.
Polygonal Model
Polygonal models, or “meshes” as they’re often called, are the most common form of 3D model found in the animation, film, and games industry, and they’re the kind we’ll focus on for the rest of the article.
The Components of a Polygonal Model
In good modeling, polygons are either four-sided (quads—the norm in character/organic modeling) or three-sided (tris—used more commonly in game modeling). Good modelers strive for efficiency and organization, trying to keep polygon counts as low as possible for the intended shape. The number of polygons in a mesh is called the poly-count, while polygon density is called resolution. The best 3D models have a high resolution where more detail is required, like a character’s hands or face, and low resolution in low detail regions of the mesh. Polygonal models are very similar to the geometric shapes you probably learned about in middle school. Just like a basic geometric cube, 3D polygonal models are comprised of faces, edges, and vertices. In fact, most complex 3D models start as a simple geometric shape, like a cube, sphere, or cylinder. These basic 3D shapes are called object primitives. The primitives are then modeled, shaped, and manipulated into whatever object the artist is trying to create.
Faces: The defining characteristic of a polygonal model is that (unlike NURBS surfaces) polygonal meshes are faceted, meaning the surface of the 3D model is comprised of hundreds or thousands of geometric faces.Edges: An edge is any point on the surface of a 3D model where two polygonal faces meet.Vertices: The point of intersection between three or more edges is called a vertex (pl. vertices). Manipulation of vertices on the x-, y-, and z-axes (affectionately referred to as “pushing and pulling verts”) is the most common technique for shaping a polygonal mesh into its final shape in traditional modeling packages like Maya, 3Ds Max, etc.
Textures and Shaders
Without textures and shaders, a 3D model wouldn’t look like much. In fact, you wouldn’t be able to see it at all. Although textures and shaders have nothing do do with the overall shape of a 3D model, they have everything to do with its visual appearance.
Shaders: A shader is a set of instructions applied to a 3D model that lets the computer know how it should be displayed. Although shading networks can be coded manually, most 3D software packages have tools that allow the artist to tweak shader parameters with great ease. Using these tools, the artist can control the way the surface of the model interacts with light, including opacity, reflectivity, specular highlight (glossiness), and dozens of others.Textures: Textures also contribute greatly to a model’s visual appearance. Textures are two-dimensional image files that are mapped onto the model’s 3D surface through a process known as texture mapping. Textures can range in complexity from simple flat color textures up to completely photorealistic surface detail.
Texturing and shading are an important aspect of the computer graphics pipeline, and becoming good at writing shader-networks or developing texture maps is a specialty in its own right. Texture and shader artists are just as instrumental in the overall look of a film or image as modelers or animators.
