Original Source: Modeling Cars in Polygons — Ebal Studios
Perhaps, the biggest defining characteristic of a car body is the fact that it is reflective! Highly reflective surfaces clearly expose your model curvature unlike matte objects. Imagine a dent or bump on a mirror versus on a dusty wooden cabinet. For all intents and purposes of this tutorial you could define a class A surface as a surface which reflects really nicely. If you go into car or industrial modeling for actual manufacturing, where you will be using a NURBS modeling software similar to Autodesk Alias or Rhinoceros 3D, you are bound to run into terms like tolerance and continuity. All the industrial technical details put aside what we are interested in for creating a car for rendering, is continuity that refers to how continuous a reflection is across a surface.
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Position continuity (G0): the surfaces are aligned and have no gaps in-between.
Tangential continuity (G1): There are no sharp edges in-between the surfaces.
Curvature continuity (G2): the surfaces are blended together with the highlights appearing as if its on a single surface.
Rate of curvature change (G3): its even more blended but the difference is very small and hardly noticeable.
To learn more about NURBS, I have a basic introduction into NURBS article which you can check or you can start exploring on your own using the term “class A surfacing” in any search engine. Below are few more links you can go through.
Alias workbench | Alias Automotive tutorials and NURBS fundamentals.
Autodesk Alias help files | Autodesk help files and basics.
Rhinoceros NURBS | NURBS definition.
NURBS basics |Theory.
Learning Alias | Interesting articles and courses about automotive modeling.
Fridolin Beisert | Basic Alias tutorials.
Vladimir Panchenko | Great resource for high-end Alias Class A surfacing tutorials.
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