Creating Elements with polygon cloning

Element of mesh is a group of polygons that are connected by their adges or built on same vertices.

You can create elements in your mesh by shift-cloning polygons.

Shift drag a polygon, release the mouse and answer Clone To Element when asked.

Fitting surface to the sketch

Now you are ready to start modeling, using your 3D sketch as a guide. Start with any part of the face.I am starting with the lips.

To make seamless connection between mirrored geometry, you can provide a polygon stripe in the middle.Polygons in this stripe should always be perpendicular to the plane of symmetry.Connection will be seamless even without final welding sides together.If you want to attach and weld the objects together when finished, you should not do it with instances.To attach the sides, do the following:Delete one side. Delete the Mesh Smooth modifier that is applied over the Edit Mesh or the Editable Mesh in the stack. Mirror with the ‘Copy’ option, not the ‘Instance’, then attach and weld with the weld selected option.

Correct Topology

Control mesh is not treated as just triangles, but as polygons.

For example, each quadratic polygon (quad) actually consists of two triangles in 3DSMAX. There is one invisible edge in each quad.

NURMS makes sense of topology.

Try to make build your mesh of quadratic polygons if possible. Use other types of polygons with care.

Here is an example of ‘good’ topology.

Incorrect topology

Geometry of the control mesh is the same, but topology is different.

Some edges made visible in this example.

Additional information about the subdivision algorithm

Generally, surface does not have to pass through the control vertices, but you can achieve this by placing three vertices to a line (vertices A, B, C on the picture). In this case surface near these vertices will behave somewhat like a Bezier spline, vertex A will serve as a knot, and B and C – as the Bezier handles.

This behavior appears on the boundary surface edges, to use this feature with other vertices, you should line up all the 8 vertices around the ‘knot’ vertex to a plane.

Surface will also intersect all Corner vertices (vertex D). Vertex B serves as a Bezier handle for knot D.

This feature of the subdivision algorithm can be very useful to get more precise control over the surface shape.

Please refer to the 3DSMAX reference for more information on particular techniques, such as mirroring objects with instance option, using Weld Target and Weld Selected commands attaching mesh objects and using Bezier splines to draw shapes.

Notes about this tutorial

In this tutorial, I‘m not using Vertex Weight feature, and Smoothing Groups feature, which are the powerful NURMS techniques. I believe that the same results can be achieved without using these features. At the same time, not relying on these features can potentially make your NURMS mesh portable to other implementations of Subdivision Surfaces (SubDivs), such as Pixar™, Maya™ and LightWave™ implementations by means of exporting non-subdivided control-mesh as polygonal object.

I describe 3DSMAX interface features as for version 3.x, but in vesion 4 it did not change much. Also, version 4 adds Editable Poly, that is slightly different from Editable Mesh, and the HSDS modifier which supports hierarchical mesh refinement and can be used in alternative or together with MeshSmooth/NURMS described here.

Notes about Subdivision Surfaces
Other implementations of Subdivision Surfaces modeling frameworks may support different features, such as hierarchical mesh refinement.Some of the industry standard renderers such as Pixar Render Man support rendering of Subdivision Surfaces on a level with NURBS.Some 3D game engines and Internet 3D viewers now support real-time Subdivision Surfaces for scalable quality and download optimization.

Intel Subdivision Surfaces

References

For those who interested in Subdivision Surfaces, I recommend to take a look at Academy Award-winning short film "Geri's Game" by Pixar. Keywords for those who interested in Subfivision Surfaces algorithms: Doo-Sabin, Catmull-Clark andChaikin’s algorithm - which can be pointed to as the first of these subdivision algorithms

That's all I knowabout NURMS business :)

Any comments and suggestions are welcome.

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Copyright 2001 by George Polevoy

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