What is 3d Edge Reinforcement?

Edge reinforcement is a technique that can be used when modeling in a 3d application. Typically it is used on subdivided objects to make some corners sharper while leaving the rest smooth.

It is hard to describe, but actually very simple when demonstrated:

3d Edge Reinforcement from darek on Vimeo.

The Quick and Dirty Explanation

You have a mesh in your 3d program. Let’s make ours a cube.

When you turn on subdivision, every side is smoothed. The cube turns into a sphere.

What if you wanted to make one side flat? You can do this by cutting a new line of edges very close to one side of the cube/sphere.

The closer the new line of edges are to the old one, the sharper the visible edge will become.

You can also use double edge reinforcement. This is simply repeating the above with a second line of edges to attain maximum sharpness.

Nice!

Why does this happen?

Catmull-Clark subdivision works by dividing each face of a mesh into 4. If there are 2 levels of subdivision each of these faces is split into 4 again. Thus, one face turns into 16.

These new faces make the object look smoother.
Because subdivision works by splitting faces, large faces will look
much smoother than before. Small faces, on the other hand, will only
create other small faces, and not change the shape much.

When reinforcing edges, what we are really doing is making many
small faces near the edges of the mesh to help it retain its original
shape

Why should I know this?

Edge reinforcement is one of the most commonly used techniques in 3d modeling. It can help make many shapes. Cubes with rounded corners, smooth cylinders, etc.

Can you spot the edge reinforcement?