NURBS Surface

A free-form surface built from a control point grid with per-point weights.

NURBS Surface is a free-form surface driven by a control point grid — terrain, cloth, car body panels, anything you cannot pin down with numbers.

Geometry

Evaluates a clamped NURBS surface from a U × V control point grid with rational weights, producing a single-sided open quad grid of (Tess U + 1) × (Tess V + 1) vertices. U runs along local X and V along local Z.

Being a one-layer surface with no thickness, the back face is invisible under standard shaders. Add the Shell modifier when you need thickness.

The initial patch size comes from the Draw-mode drag (w and d in a script); everything after that is defined by the control points. A higher Degree smooths the surface, a lower one hugs the control points more tightly.

Parameters

Label	Script key	Default	Range	Description
Controls U	`cu`	4	2 ~ 8	Control points along U (local X)
Controls V	`cv`	4	2 ~ 8	Control points along V (local Z)
Degree	`ord`	3	1 ~ 5	Curve degree — higher is smoother
Tess U	`widthsegs`	16	1 ~ 128	Tessellation along U (output mesh divisions)
Tess V	`depthsegs`	16	1 ~ 128	Tessellation along V

Control point positions and weights are editable only in the editor. A script can set counts, degree and tessellation. Changing the Controls U / V counts reinitializes the grid to a flat plane, so decide the counts before shaping.

How to create

Drag in empty space to set the size of the initial flat patch — the control point grid is rebuilt continuously while you drag.
Click to finish. There is no height stage; the shape comes from the control points afterwards.

Scene view editing

Uses control point handles instead of size handles.

Dragging a CP sphere moves it freely in screen space; grabbing a CP that is part of the selection moves the whole selection.
The gizmo at the selection center moves the whole selection by axis or plane.
Drag in empty space to range-select (Shift adds, Ctrl / Cmd toggles). Clicking empty space clears the selection.
Selected Point Weight in the Inspector adjusts the weight of the selected CP — a higher weight pulls the surface toward it.
Reset Control Points returns the grid to a flat plane.

Tips

Start with few Controls U / V — 4 × 4 to establish the big shape, then add more when needed.

Tess U / V is output density: 16 × 16 is 256 quads, 128 × 128 is 16,384.

For broad surfaces such as terrain, tiling several NURBS patches is easier to manage than pushing Tess higher.

Script

In a script this shape is written as nurbs.

nurbs "Hillside" w=8 d=8 cu=4 cv=4 ord=3 widthsegs=32 depthsegs=32 @0,0,0
nurbs "Panel" cu=3 cv=3 ord=2 @10,0,0
  mod shell thickness=0.05