3D Model Components - Vertices, Edges, Polygons & More

Anatomy of a 3D Model

3D Rendering, display figures, outsider
A 3D Model is a mathematical representation of any three-dimensional object (real or imagined) in a 3D software environment. Westend61 / Getty Images

3D Models are one of the essential building blocks of 3D computer graphics. Without them, ?there would be no computer animation—no Toy Story, no Wall-E, no big green ogre.

There'd be no 3D gaming, which means we never got to explore Hyrule in Ocarina of Time, and Master Chief was never on Halo. There'd be no Transformers movies (at least the way we know them today), and car commercials couldn't possibly look anything like this one.

Every object, character, and environment, in every computer animated movie or 3D video game, is comprised of 3D models. So yes, they're pretty important in the world of CG.

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, and can be scaled, rotated, or freely modified. The process of creating and shaping a 3D model is known as 3d modeling.

Types of 3D Models

There are two primary types of 3D models that are used in the film & games industry, the most apparent differences being in 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).

  1. NURBS Surface: A Non-uniform rational B-spline, or NURBS surface is a smooth surface model created through the use of Bezier curves (like a 3D version of the the MS Paint pen tool). To form a NURBS surface, the artist draws two or more curves in 3D space, which can be 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 therefore most commonly used in modeling for engineering and automotive design.???
  1. 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'll be the kind that we'll focus on for the rest of the article.??

The Components of a Polygonal Model

  • 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.

    In good modeling, polgons 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 high resolution? where more detail is required—like a character's hands or face, and low resolution in low detail regions of the mesh. Typically, the higher the overall resolution of a model, the smoother it will appear in a final render. Lower resolution meshes look boxy (remember Mario 64?).

    • 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 it's final shape in traditional modeling packages like Maya, 3Ds Max, etc. (Techniques are very, very different in sculpting applications like ZBrush or Mudbox.)

      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 can then be modeled, shaped, and manipulated into whatever object the artist is trying to create (as much as we'd like to go into detail, we'll cover the process of 3D modeling in a separate article).

      There's one more component of 3D models that needs to be addressed:

      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 can be 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 it's own right. Texture and shader artists are just as instrumental in the overall look of a film or image as modelers or animators.

      You made it!

      Hopefully, at this point, you know a little bit more about 3D models and their primary characteristics. At their core, 3D models are just complex geometric shapes with hundreds of little polygonal faces. While, it's undoubtedly fun to read about 3D models, it's even more exciting to ?make them yourself.

      Check out our other beginner articles: This article is the second in our new beginner series meant to ease newcomers into the world of 3D. If you missed the first article and are interested in an expanded explanation of the term "3D" as it pertains to film, games and ?computer graphics, check it out after the jump: 3D Defined >>