Class A surfaces in Rhino


I’ve heard that CATIA (from DDS) can achieve class A surfaces.
Can anyone help me understand what does it means (or send me links about it) and what does it has that Rhino doesn’t?


Class A surfaces = industry buzzword, mostly meaningless and subject to endless debate.

Class A surfaces is a term used in automotive design to describe a set of freeform surfaces of high efficiency and quality. Although, strictly, it is nothing more than saying the surfaces have curvature and tangency alignment - to ideal aesthetical reflection quality, many people interpret class A surfaces to have G2 (or even G3) curvature continuity to one another (see freeform surface modelling).

Rhino can certainly make “Class A” surfaces by any definition in the hands of a sufficiently experienced modeler. The REAL debate is having tools that allow you to easily analyze and modify your “Class A” surfaces in real time. That can only really be provided by a plug-in such as VSR.

My 2¢… --Mitch


Class A = marketing strategy to increase the cost of a surface modeler.

It’s like the dpi in graphics.
What is it better a 300dpi postage stamp or a 72dpi A0 paper ?

The reality it’s no one never define the quality to be reach.


Does it worth to acquire this plug-in?


Depends on what you do, I guess… If you’re going to be modeling automotive type surfaces in Rhino, I recommend you get it right now, as there is a sale on

(and no, I don’t work for VSR/Autodesk, nor do I have any financial interest here)



Rhino is a NURBS modeling tool like Autodesk Alias, Catia and many others, meaning Rhino certainty can do class-A surfaces without any plug-ins. People can’t model in Rhinoceros(for instance, the class-A surfaces) VSR won’t help, neither Autodesk Alias. I just found a good question and answers about class-A surfaces in relation to Single Span modeling…
To better understand the topic.


I totally missed this. Thanks for bringing it up again.

(Marc Gibeault) #8

It’s useful to remember where this term comes from.
In most products, you have the A-surface, that the user is seeing, and you have the B-surface, that is hidden.
A car hood must have excellent surface continuity on it’s outside surfaces but can have simple tangency on it’s inside surfaces, generally hidden and most likely covered with insulation.
When one spoke of A-class surfaces, it meant “of sufficient visual quality to be seen by the customer”.
I worked with a few CAD models of parts from big automakers. All had great continuity quality between surfaces on external surfaces but nothing Rhino can’t match. The road to get there is easier when you can adjust continuity on several edges / surfaces at the same time though.
B-side surfaces where more crude with simple fillets between surfaces.


to my mind the real point is not only the quality but also time and effort to get there (while keeping geometrie flexible).
see this video link from icem/catia:


I have watched some tutorials about T-Splines and worked with it a little bit then. However, the conversion from SubD to NURBS is a mess: small surfaces with lots of control points. Isn’t it against Class A surfaces. In one hand there’s a great continuity, but on the other, non-editable surfaces.


I don’t use T-Splines myself, but as far as I’ve seen it is NOT the tool to use when designing very high quality editable surfaces with edge continuity control and a simple point structure. That said, that kind of surface design is not always necessary to create a good product, it depends on what you’re designing, and for whom…



What Mitch says is correct, but remember the most important thing about “Class A” surfacing: what it really means is whatever the Alias guys are trying to sell you this year. And they own T-Splines now, ergo T-Splines are the mostest Classiest, A-iest surfaces ever. It’s a marketing buzzword.


Hi Joodys, if I’m not wrong Mitch suggested you VSR and not T-Splines, both plugins technology were bought by Autodesk but they are very different and powerful plugins for Rhino.
VSR is the one that let you work inside rhino with a workflow similar to Icem, and T-Splines is designed to work with Sub-D technics.
I use both plugins for different kind of products or phases of a project.


Yes Jim!
exactly ! :wink:


The terminology ‘Class A’, as Mitch has stated, is used primarily in the automotive industry to describe a particular type of surface - continuity matched Bezier (aka single span) surfaces. Rhino can, of course, create these surfaces but matching and analysing them is more than a little difficult - and sometimes not possible. The VSR tools are the first step in Rhino getting these features and the capability of creating explicit surfaces like Alias.

T-Splines does not create Class A surfaces; when you convert a TS mesh to NURBS the result is a multi span Degree 3 surface.

In practice, you might use T-Splines to rough out some concepts and then VSR tools to produce some initial surfaces.

‘Class A’ is often mis-defined and derided by some as marketing bullshit, but if you want to work beyond concepts in the automotive industry then it’s a reality.

Simply Rhino

(Pascal Golay) #16

Hi Phil- just to confuse the thing a little more, it sounds like your description of Class A is about how these are made - single spans etc.- in the auto industry, but I’d assumed the designation or label would really have more to do with ‘how good are the surfaces’ than ‘how did you make them’ …? I realize currently many if not all so called class A surfaces may be made using Bezier patches, but that in itself is not a criterion for class A, is it? Or is it?




Hi Pascal, I really think that depends on who you talk to :smile:. It’s not, of course, an ‘official’ terminology but certainly amongst automotive designers and high end surfacing modellers then my experience is that Class A = continuity matched Bezier patches. Phil


At the end:

no matter who you are or how much experience you have, no one really know what’s the Class A.

We found the modeling Chimera !

Ah ah ah :smiley:


It isn’t a myth.

It is a widely understood terminology used within certain industries.

If you took on a contract in the automotive or product design sector and were asked to create ‘Class A’ surfaces then your client would expect continuity matched Bezier patches.