Surface Structure

Surfaces are similar to Curves, in that they use Bézier or NURBS splines to produce smooth geometry that follows a set of control points. The main difference, of course, is that a Curve produces a line while a Surface produces a sheet.

A Surface object can contain multiple disconnected surfaces. The one that’s selected in Edit Mode is referred to as the “active spline.”

Control Point Grid

While a Surface can be compared to a mesh with a Subdivision Surface Modifier, it’s more restrictive because the control points must be strictly arranged in a grid: each “row” indicated by a yellow line must have the same number of control points, and so does each “column” indicated by a pink line. The only way to extend the surface is by extruding a complete row or column.

The Active Spline panel controls whether the surface is cyclic (closed) in each direction of the grid, and whether Bézier or NURBS should be used.

Weights

The shape can be further tweaked by changing the weight of individual control points in the Transform Panel found in the Sidebar.

The property is called W; while there is also one called Weight, this is the Goal Weight for soft body simulations.

A control point with a higher weight pulls the surface towards it.

Note

If all control points have the same weight, they cancel each other out and the surface ends up looking the same as before. The weights must be different for there to be an effect.

Weights are necessary to achieve certain “pure” shapes like cylinders or spheres. The primitives in the Add menu have these preconfigured.

Control point weights on a spherical Surface.