Lesson6 Curves and Surfaces

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In Alias, the surface tools are set to ‘Create History’ by default. This means that any changes to the curves will modify the surface shape.

Many other CAD systems rely on this type of history connection to maintain a history tree throughout the modeling process, and it is an inherent part of the CAD data.

Alias is different : Construction History is optional, and will apply to some parts of the model and not others. This has the disadvantage that one change to a main curve may not cause the whole model to update. However, it makes the model much more flexible and free to change during rapid design development.

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The second way to use construction history to update and change your surfaces is through changing the settings in a control window.

Not all surface tools have a ‘Control Window’, some only have an ‘Option Window’. The difference is that the settings in an option window can only be chosen once, before the curves are chosen.

With a Control Window, you can always return to the settings and make changes at any time (as long as the construction history has not been deleted).

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The History View in Alias may look similar to a ‘history tree’ found in engineering CAD systems, but it doesn’t work in the same way.

The Alias History View is for viewing the model links and history, and in practice isn’t used regularly. Whereas a CAD system history tree is normally a fundamental part of the CAD model structure.

The most useful tool is the ‘suspend rebuilds’ option. If you have a large model, with lots of history connections, then modifying a CV on an early curve can cause the system to pause, while it is updating all the dependent surfaces, which makes interactive sculpting difficult. This temporarily suspends these rebuilds while you sculpt a new shape for a curve, and removing it then allows all the rebuilds to be done afterwards.

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Focus on Curve Quality

The structure of your curves will directly affect the structure of your surfaces, and so most of the time is spent creating and refining the curves.

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Minimum number of curves

There are many shapes that could be built using a variety of surface tools. Always try to use the minimum number of curves to achieve a shape.

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There are too many individual options for each tool to go through them one-by-one in a lecture, so you will need to explore and experiment with them to expand your skill and knowledge.

Learning by Exploring

Particularly if you have experience with other CAD systems, you can learn to use the surface tools by just trying them, and following the prompts.

Learning by Reading

To get information on all the options for each surface, access the help documentation.

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Further information on the revolve tool can be found in the What’s new videos ;

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Cutting Holes in NURBS Surfaces You cannot successfully create a hole in a NURBS surface by moving CVs and Hulls. One exception is periodic surfaces such as partial spheres and cylinders, which have a ‘hole’ that is actually the edge of the surface. Another – unnecessarily complex – method is to work out a patch layout of 4-sided surfaces to create the effect of a hole. Trimming is a much easier method of modifying the surface outline without using the CVs to modify the shape.

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The tools for trimming are found on the Surface Edit Palette. The first set of tools are for creating a curve-on-surface, which is the name for the line that defines the trim. This is then used to specify which parts of the surface to keep and which to discard. This process is the same as in many other CAD systems, but often the intermediate stage of seeing the curve-on-surface is hidden from the user (even though it has to be created for the internal mathematics). With Alias, there is a workflow called 3D trimming that works in the same way, and can offer a quicker workflow. But to start with, each separate process will be covered so that you have a full understanding of how trimming works.

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By default, the Intersect option window is set to create curves-on-surface on both surfaces (or sets of surfaces)

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By default, Project creates a curve-on-surface ready for trimming.

You can also create a normal curve which can then be used for building further curves and surfaces

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Lesson6 Curves and Surfaces

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