Before we dive in and begin creating our scene it’s probably a good idea to take a step back and look at what we will be working with. I love to mode with Subdivision Surfaces, or limit surfaces, a method which has been around for a while now and is widely used for creating high-end 3D models.
As it stands, working on a highly detailed model comprised of many millions of polygons is a nightmare, not only for the hardware but also for general manipulation. Subdivision Surfaces give the us the freedom to work on a low-resolution model, known as a cage, base, or control mesh, safe in the knowledge that a simple button or key press can produce a smoother, higher-resolution model, which in turn can be worked further by manipulating the control mesh.
You can see the control mesh on the left, below. This is the rougher, more angular model that is built initially.
Next to this is the model converted to a subdivision surface. Notice how nice and smooth it is. You can also see the wireframe from the base mesh traced across its surface, showing its origins.
Finally the subdivision surface model has been converted back into polygons. When comparing this to the previous model you can see how much denser the mesh is, meaning it would be more difficult to edit or manipulate.
Here’s the Science Bit
So how do they work? Well, in laymen’s terms, all that happens is the surface of the control mesh is subdivided—hence the name. New vertices and faces are added with their position calculated using the original vertex positions and one of two refinement schemes (see below).
The two schemes, “Approximation” and “Interpolation,” differ in that the latter will try to retain the original shape of the mesh, whereas approximation will result in a smoother surface at the cost of the original shape.
Popular applications like Maya, 3D Studio Max, Silo, and Softimage XSI rely on an approximation algorithm called Catmull–Clark, created by Edwin Catmull and Jim Clark in 1978. The creation of the algorithm landed Edwin—the current president of Walt Disney Animation Studios and Pixar Animation Studios—an Academy Award in 2006 for Technical Achievement.
Memory
Working with subdivision surfaces gets better. Even when you’ve converted the model into a subdivision surface, you can still work on the control mesh, viewing any modifications you make in real time as they move up the chain and affect the smoother model (see below).
Now thats out of the way we can move on and start building Mandy.
