Introduction
The NURMS (Non-Rational Mesh Smooth) or Subdivision Surface technique uses low-polygonal mesh to control the shape of the smooth surface.

This tutorial demonstrates my favorite techniques for symmetric NURMS modeling and 3D sketching, enough to build the model, similar to what you see in the first pictures. I realize that the model you see at the pictures is not suited for very advanced animation, which could require different topology and more refinement.

Tutorial
First, find any suitable reference for your model. Setting up the pictures as a view-port background is a common technique, but I prefer drawing a sketch in 3D.

This is how your scene will look at some stage.

Thin gray or dark blue lines show the initial 3D sketch.

The red lines you see over the surface are a kind of low-polygonal model, which serves as NURMS control mesh. It is slightly different from typical low-poly in that it is not suited for visualization itself. It only can be used as a rough model representation.

NURMS behaves much like NURBS power 3 with the difference that NURMS can be of arbitrary topology with no UV -- quadratic restriction.

Note that control mesh vertices lie somewhat outside the actual surface, if the surface is convex, and inside the surface if the surface is concave.

This surface behavior is different form 3DSMAX Bezier Patch surfaces, in which the surface must cross each vertex.

Please see “Additional information about the subdivision algorithm” below.

3D sketching

Draw profile and front view curves first.

These two curves can stay ‘2D’.

Draw as many curves in 3D as you need.

Choosing the correct curves is the main thing at this time.

Created curves should give you a sense of volume in perspective or user view-ports, not only correct shapes in front and side view-ports.

Align curves, so the curves that should intersect lie as close to each other as possible at the ‘intersection’ point.

Use the mirror modifier or the mirror tool to create symmetrical curves.

If you use the mirror tool, do not forget to turn the ‘instance’ option on, so the symmetric object will stay symmetric after modifying the original object.

I recommend doing all the modeling around the center of the world coordinate system.

Allow yourself as much time as you can at this stage and create a perfect shape.

This will save you a lot of time creating actual geometry.

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Copyright 2001 by George Polevoy

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