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ACKNOWLEDGEMENTS

Our sincere thanks go to David Shall, Audrey Carstens, Uwe Rossbacher, Thomas Heermann, Alexander Fuchs, Thomas Sahlin, Dagmar Miller and all the other people who encouraged us and helped with this tutorial.Special thanks go to the French Technicon Design Team who did
the inital design and modelling of the Aerospeed car used in this tutorial.Further thanks must go to the German Technicon Design Team
for the final design and modelling of this car.Very special thanks go to the team of 16 Colours for the layout,
graphic design and the programming of the PDF.Raphaël Sulpice, Nicolas Caquelin,Luc Bonnot, Guillaume Diet, Benjamin Moussa.Stev Sommer, Frederik Wallmander, Katharina Roos,Henrik Ihlefeld, Christoffer Brenander.Alex Ziegler, Tom Heinen, Victor Stelmasuk.

Werner Strathaus

Preface

Introduction to ‘Class A surfacing’
‘Class A surfacing’ is to produce mathematical surfaces to the most exacting standard.
Once completed the ‘A Class surface’ is the final output of styling design. These surfaces are the ‘Master’ for making the tools that produces the product itself.
‘Class A’ surfacing is one of the most complex and tedious 3D computer modeling tasks you can do.
‘Class A’ surface development occurs in the final phase of a project, when constraints are much tighter to adhere to.
Modeling under these conditions is very hard without adoption of certain ‘surface basics’ rules.
3D computer modeling is still based on the knowledge and skill set of the individual user.
Therefore productivity and surface quality is user dependent.
The surfacing task can begin from the scan of a physical model, as in this tutorial, but it can also start from 2D sketch or verbal input. In most cases it is the continuation of a concept 3D digital model.
Most of the time you will also need to be aware of and include flanges, draft angles, tool split lines and other engineering constraints
In the tutorial these are not included.
To include them would put even more constraints on the modeling/surfacing itself.
This tutorial demonstrates only one small part of ‘class A’ surfacing, but a very important element of creating good quality surfaces.

When you are starting a project or a part, always take some time to think how you will build this before you start.
It is not a good idea to rush in the beginning of a project.
To be successful and to achieve that right quality in the time given you need a ‘strategy’. Without this you can find yourself in a corner from which you can never escape a dead end.
These points below are, in my opinion, the most important, basic rules to succeed.
• It is very important to have a strategy on methodology,
surface layout and surface construction.
• Always try to build the surfaces to allow easy modification.
• Keep the surfaces as simple as possible.
• Always try to build to an intersection.
By following these basic rules you have come a long way to succeeding in your modeling.
Good luck.

Thomas Sahlin

Digital Design Manager
GME Design

AIM OF THIS TUTORIAL

This tutorial has been created due to an increased demand in the automotive industry in recent times for digital modelling work of very high quality. We are therefore trying to explain to the tutorial user what Class-A surfacing in the field of automotive modelling means and how the required high surface quality can be achieved with Autodesk Studio.This is done using teaching sessions to show the modelling of selected exterior parts based on scan data from a 1:4 clay model and further design changes. The tutorial covers a wide range of Class-A modelling aspects but is by no means comprehensive, because this is such a wide-ranging topic. However, we believe that this tutorial will provide its user with a good understanding of the Class-A surfacing theory and the basic knowledge of the strategies used to develop his Class-A surfacing skills further.The tutorial is aimed at Alias modellers with experience in the field of automotive design and a good general knowledge of the Autodesk AutoStudio modelling tools and their options.

Introduction Class-A surfacing in the automotive design process
The philosophy of Class-A surfacing
Numerical Class-A surfacing definition
Nurbs and Bezier geometry
Different types of body architecture

Class-A surfacing in the automotive design process

Any product development process of the automotive industry is divided into phases beginning with Global Marketing Research and ending with Start of Production (SOP). Amongst the OEM´s and suppliers the defined gates within their product development process can differ drastically. Some work with a lot of iterative gates others have just some important big gates to pass. In any case the surfacer‘s work is an iterative process, constantly increasing aesthetical expression, engineering & design content and the mathematical quality of all visually recognisable surfaces of the car.

The workload for Class-A surfacing work is ramping up towards the end of the product development process. It is the amount of implemented feasibility information, styling details and steps within the Class-A surfacing process itself that differentiates Class-A surfacing work from conceptual surfacing much more than tolerance settings of the used software. For this reason and in order to continue the entire surfacing process with Alias Studio tools as one software system from Concept to Class-A, we nowadays see more and more the tendency to implement basic Class-A surfacing methodologies into the early concept modelling phase. Using principal Class-A modelling methods will also help you to generate quickly high quality concept data that are easy to change and can be used during the whole surfacing process.

The Philosophy of Class-A Surfacing

Class A Surfacing is the art of digital surface generation at the highest aesthetic level reflected by the minimum mathematical information needed.

Numerical Class-A surfacing definition:

A definition of the numerical Class-A settings for your Alias work is usually defined by the customer. This definition has to be reflected within your Construction Options in Alias. Basically, two sets of parameters define these settings:One is related to the surface quality definition as such,the other as a set of parameters related to the requirements of the client‘s major CAD system.Alias provides you with default Construction Presets of the most common engineering CAD systems.
Tip:
Check your client‘s requirements carefully. They may differ from the default engineering system settings used in the Construction Presets, even if the system is listed!

Nurbs and Bezier Geometry:

Bezier and NURBS surfaces are closely related.Pierre Bézier developed the algorithm that mathematically describes a free form surface shape by the position of its anchor points. The NURBS algorithm is a further developed Bezier algorithm with the advantage or disadvantage to contain help geometry (spans) that enables the single surface to do more drastic changes in direction than a Bezier surface ever can. In other words it is possible to incorporate several Bezier surfaces in one single NURBS surface. It is most obvious that NURBS surfaces are much harder to control than Bezier surfaces. For this reason Class-A surfacing is so heavily depending on Bezier structure surfaces.

Different Types of Body Architecture:

Similar to a human body, the body architecture and aesthetic appearance of a car is not dependent on its size.Of course the differences between coupé, limousine, estate and convertible are defined by different body architectures. Thereby the biggest differences between these types of cars are due to the way the greenhouses are built, the amount of pillars that are holding up the roof and the number of doors a car has.

In this respect, what is important for Class-A surface complexity?

• Whether we have a sidewall that is basically built out of one big slap (e.g. Mercedes S-Class 1991) or if the sidewall is defined by a prominent shoulder (e.g. Volvo S60).
• Whether the styling is emotional or rational. Emotional design usually increases surface complexity. The transitions of side wall into front, bonnet, A- and C-pillar and the back of the car are usually more curved and more complex than on cars with a rational design development (such as the Hummer for example ,even though a Hummer causes emotional outbreaks with some people).The Lotus Esprit might be an exception!
• Most complex areas:A-pillar transition into bonnet and fender.C-pillar transition into sidewall and back-end Front facia and rear end.

Welcome to the Class-A Surfacing Session 1

Hello, my name is Werner Strattrathaus I am a design consultant in the Technicon Design Studio in Rüsselsheim, Germany.

Welcome to the interactive Class-A surfacing tutorial
of Autodesk AutoStudio.
This session is tailor-made for advanced Studio users aiming to achieve ultimate quality surface creation.
Let me spend some time with you to go through the build up of a sports car exterior at Class-A surfacing standard using the Autodesk Studio tools.

High Res Videos will be available soon. Stay tuned.

1. Starting point: input data

1.1 Review the given Information and Adjust the display settings

• In session 1 I will talk about the starting point "Input Data" and how to review the given information.
• We will learn how to adjust the Display Settings and how to use the Diagnostic Shader tools to be able to evaluate the quality and the general surface conditions of the scanned polygon data of a 1:4 size clay model blown up to a full scale size data set.

Open the "Aerospeed" scan data and make sure to accept the Technicon Design Class-A construction options. Now the mesh of half of the car will be displayed in a very unreadable way. In order to achieve better readability of the shape of your object, go to the Control Panel and open the Display options and then the Transparency Box and change the Mesh Transparency Setting to 0.8 or adjust it using the slider until you get a nice and readable appearance of the half car.Complete the car using the Mirror Function and start building up your own individual Modeling-Shelf for the scan rebuild workflow! Open up the Mirror Function under Edit>Duplicate>Mirror, tap the XZ box and move the Duplicate Mirror Icon into the empty Shelf-Set. Save the Shelf-Set and rename it to „Scan Rebuild“.Click on the Mirror Icon and then the polygon mesh. The complete car appears! You have just displayed and adjusted the appearance of your scan data and have started to individualize your workflow to rebuild the scan data!

1.2 Diagnostic Shader Usage for Scan Data Evaluation.

Go into the Diagnostic Shader Toolbox and open the option box by clicking the arrow. Hit the Curvature Evaluation icon, change the Evaluation Type to Mean and set the Curvature Color Scale Value to 3. Watch the result.

The curvature of the mirrored mesh of the car are showed as opposite values - colours to the original. The reason is that the mirrored and the copied meshes and surfaces always have their normal orientation opposite to the originals.

To equalize the mesn orientation open the Mesh Toolbox of the Palette. Activate the Reverse Mesh Orientation tool and activate the mirrored part of the mesh.
Then click on Reverse Mesh box in the modeling window and the yellow color clips to blue - the same as the original side.

Deactivate the copied mesh and the Reverse Mesh tool and both sides of the car indicate the same curvature values.

Look at the curvature plot of the polygon data. Orange to red indicates concave and blue to purple convex areas of the car.

This option not only shows us the many dents and irregularities of the blown up scan data but also shut lines, crease lines and radii are easy to read in this display mode.

The Stripe Shader:
Click on the Stripe or Zebra Shader icon in the Diagnostic Shading Box.

The stripe shader usually allows us to evaluate whether we have good continuity conditions between surfaces and equal curvature acceleration within them or not.

If the polygon data are displayed in this jagged way in stripe shader mode, it indicates lots of little irregularities of the skin even though the main flow of the surface can be good. Breaks in the main surface flow become apparent if the stripes show sudden angles or uneven waves.

For scan data the stripe shader is very important and useful to review the characteristics of the general surface flow of the object.
Stripe shader on scan data immediately highlight areas of problematic surfacing and unresolved design problems.

When looking at the rebuilt surfaces in the stripe shader mode, the final surfaces should appear without any jags, dots and kinks observing the same flow and position of the stripes as the scan data (except for weird surface areas).

The option to adjust the transparency and the number of repeats of stripes is helpful and necessary. We will explore these options further and in depth later on in this tutorial.