2. Technicon Design Construction Options for Class-A surfacing

2.1 Recommended Class-A Construction Settings

The recommended Technicon Design Class-A surfacing settings are a harmonization of different specifications from various international OEMs incorporating Technicon‘s long experience in the automotive design process.

In any case you should follow the specifications given by your client or the settings of the system you have to hand the data over to. If there are no specifications the Technicon Design Class-A surfacing settings are a good recommendation.

2.2 The influence of the rebuild tolerance on Class-A surfacing work

The rebuild tolerance is the amount of deviation between the scan data and your new rebuilt surfaces. A maximum tolerance is usually given by your client.

Class-A expectations such as perfect surface flow under G3 conditions are often not achievable within the given rebuild deviation distance.

A hand-made clay exterior can hardly incorporate the same amount of information (package info, hard points, engineering criteria, surface continuity, highlighting etc.) as we usually have to do in our CAD work (all at the same time).

A good Alias Modeler communicates where and why he does not stick to the requested rebuild tolerance, thus assisting design and engineering.

3. Data Screening

In session 3 we divide the scan data into pieces related to the body architecture of the car and start to organise the file in a proper and clear way.

3.1 Mesh subset

First go to the Mesh Tools of the Palette and drag the Mesh Subset (mmb pressed) Icon into your Shelf-Set. Switch to top view and use the Look At command to center the car on the screen. Delete the mirrored side of the mesh and zoom in the half windscreen as much as possible. Activate the Mesh Subset tool in your Shelf-Set, then activate the mesh with a click (lmb) and it appears pink! Then click (lmb) point by point around the area of the windscreen until the black line surrounds the area you want to separate.Click (lmb) the Select button in the Modeling Window (bottom right) and the selected area will appear blue. If you then click the Subset button the selected part of the mesh is separated from the rest.

Exercise:

Please separate front and rear wheels along the wheel arches!

3.2 File Organization

Proper file organization is most important for a good structured workflow.

Layer usage and clear naming is the key to information for yourself but also for others you might share your work with. Develop a sensible self-explanatory way of layer naming and separate between reference, work in progress and final data.

Use the layer coloring to visualize the structure.

3.2.1 Layer Organization & usage

So far we already have separated the mesh of our car into four parts. Front wheel, rear wheel, windscreen and body.It is time now to assign them to well named Layers. Create a New Layer and name it Mesh Complete. To this layer we will assign the complete original mesh. Therefore, open up the original file in a new stage again and then copy and paste the mesh back into the other stage to assign it to the layer "Mesh Complete". Then go back to the Stage Editor and delete the latest stage. Now hide the layer by disabling the Layer Visible option. Name the next layer „Body Mesh“ and Assign the whole body of the car to it. Another layer will be named „Wheel Mesh“ to which we assign the two wheels and hide them. Layer 4 should be called Windscreen Mesh. Assign the windscreen to it and activate the Symmetry option.

3.2.2 Layer categories

The Layer Category Window provides a good functionality to sort and reduce the amount of layers displayed in the Layer Bar on top of the Modeling Window. Open the Editor Box of the Layer Categories. By default we have three layer categories as such. The Arrow/Square icon selects all layer of a category. The Eye icon displays or hides all layers of a category. Open up a new layer category by pressing (lmb) at Category on top of the icons in the Category Window and select New Category. Rename the new category into Mesh Layers. The white bar behind “Mesh Layers” indicates the active status of the category. Click the Select icon of the All Layers category and choose Add Layers. A 5 appears in the little right box of this category, it shows the number of Layers related to this category.

Tip:
Each layer can belong to several Categories. For example the layer "Windscreen Mesh" can belong to the categories "All Layers", "Mesh Layers" and "Work in progress".

Use this functionality in a flexible manner as you need it.

4. Aerospeed Architecture

Before we actually start to rebuild our first surfaces, let's spend some time to take a look at the general surface architecture of the "Aerospeed" car. For a closer examination of the car architecture we observe just the generic volume and leave out all details that can be seen as cut-outs or add-ons (eg. air intakes, depressions, fins, shut lines etc.).
The architecture of this specific car is based on a mixture of clearly defined easy to separate surfaces and some surfaces in between that are floating into each other and have vague boundaries.

Windscreen, Roof, Back-end

We have easy windscreen, roof and back-end surfaces, just slightly over-crowned in two directions. These surfaces sweep along the roofline all along the upper sidewall boundary down to the back-end. The main slaps of windscreen roof and back-end share theoretical edges. The final surface layout has got additional surfaces to enable a smooth transition between the main slaps of the greenhouse. These additional surfaces will become our first secondary surfaces.

The curvature of the roofline is drastically accelerated towards the back-end so that the back-end roof surfaces are floating into each other. We will leave out the details of the roof, the flat middle surfaces and the glass strip because of an expected design change of the roof top.

Sidewall, Front & Rear Fender

The sidewall is built out of four main surfaces. Two of them running towards the front end the other two towards the back. Primarily they are intersected by the front and rear fenders. The way the rear fender blends into the sidewall is the most complicated part of this car.
We will spend some time later to explore this area. The transition from the sidewall to the front fender is relatively easy if the correct modeling strategy is used.

Bonnet & Front-End

The conditions here are not too complicated. The bonnet top is built of two intersecting main surfaces, one in blue with a history as kind of an elongated offset of half the side of the windscreen. And a red surface, stretched between the sweep of the fender and the upper surface of the front-end and then curved backwards to run out well below the middle part of the bonnet. Transitional surfaces between them enable the change of direction from the middle of the bonnet into the windscreen.

4.1 Surface hierarchy

The organisation of surfaces and the layout of the patches is very much related to the architecture of the car. A clear hierarchy of the surfaces leads to a good patch layout.

4.1.1 Primary surfaces

Aerospeed‘s primary surfaces are the main slaps of the general exterior volume that share the same boundaries or intersect each other.

4.1.2 Secondary surfaces

Fillets and floating surfaces between the big slaps that essentially define the car body become secondary surfaces.

Ideally, the whole volume of the car can be represented by primary and secondary surfaces. Of course the main body parts (for example sidewall to roof) will then have sharp-edged connections and no gaps.

Notice:
In order to achieve Class-A surface quality for primary and secondary surfaces, the surfaces must have G3 Curvature conditions in relation to each other. No spans (Bezier structures) and no more than 7 degrees (8 CVs) in u and v direction!

4.1.3 Tertiary surfaces

Surfaces that smooth out the edges or intersections of the main body parts, such as sidewall and roof or wheel arch and bonnet, are defined as tertiary surfaces.

4.1.4 Rank four surfaces

These surfaces are typically interfacial surfaces between primary, secondary or tertiary surfaces and engineering driven surfaces such as drafts and flanges. Typical examples are fillets around the A-surface of bumper / hood / doors and other body parts to their engineering flanges.

Notice:
Class-A surface quality for tertiary and rank four surfaces means that these surfaces must have a minimum of G2 Curvature conditions (G3 is desirable) in relation to primary and secondary surfaces. Up to 7 spans (no spans desirable) and no more than 7 degrees (8 CVs) in u and v direction!

A minimum of tangent continuity between rank four surfaces and engineering surfaces is required

4.2 Surface patch layout

As a general rule, create as few patches as possible but enough to reflect the required morphology of the object.
Keep the structure of each patch simple (single span surfacing) to assure they are easy to control!
Avoid multiple curvature directions (S-shape) in single patches.
Adjoining patches should have a direction change or curvature acceleration in just one direction.
Although we have hardly ever 90 degree surface corners, the footprint of each patch (untrimmed) should be almost rectangular or square.
Avoid heavy rhomboidal footprints.