Symmetrical Modeling

What’s New in Alias 2010 > Modeling >

Brand new functionality lets you enter a symmetric modeling mode where you can select geometry and modify it in a symmetric manner by moving controls (CVs, edit points, and so on) on one side, and having the corresponding controls on the symmetric half automatically move in the opposite direction.

The symmetry plane is defined by the default symmetry plane for the layer the curve or surface belongs to. This plane can be modified by using Layers > Symmetry > Set Plane. If you move the object, the symmetry plane moves with it.

To modify a curve across a centerline

Create a curve across the Y axis.
Choose Object Edit > Symmetric Modeling.
Select the curve.
Symmetric constraint is applied to the curve. If the curve is not symmetric, it is modified to be symmetric.

A yellow symmetry plane is displayed. This plane corresponds to the default symmetry plane for the layer the object belongs to (XZ plane by default). You can modify it by using Layers > Symmetry > Set Plane.
Pick one or more CVs on one side of the curve.
Blue circles appear around the corresponding CVs on the symmetric half.
Move the CVs (with Transform > Move or the Move CV tool).

The selected CVs follow the mouse. The symmetric CVs move in the negative direction on the symmetric side of the plane.

The curve has construction history so that any subsequent operation on the CVs will continue to maintain symmetry across the plane. If you want to remove the symmetry constraint from the geometry, delete the construction history.

If the whole curve is moved, the symmetry plane moves with it but is drawn in a different color to differentiate it from the layer symmetry plane.

Inputs and selection

Regular curves and surfaces can be selected, as well as Blend Curves. In the case of Blend Curves, only the position of the blend points is supported by symmetric modeling (and not other constraints such as tangent scaling). Blend curves where any blend point is connected to geometry are not supported. Keypoint curves can also be used, but will lose their keypoint attributes.
Several curves and surfaces can be selected at once.
Geometry can be selected either before or after entering the tool. Symmetry constraints are applied to each curve or surface individually.

Modification

CVs, edit points, and blend points can be modified symmetrically.
If the input curve or surface is not symmetric, the tool modifies the controls of the model to ensure that it is symmetric. The position of the controls from the beginning of the curve or surface are applied to the symmetric partners at the end of the curve or surface. Click the Flip Master Side button to have it work the other way around.
If a control (CV, edit point, or blend point) is selected prior to entering the Symmetric Modeling tool, the side of the object containing the picked control becomes the master side and is not modified when the object is made symmetric.
Any transformation tool can be applied to the controls including Move, Rotate, Scale, Non Proportional Scale, Move CV (XYZ, Slide, NUV, Project) or Proportional Modification.
Once the Symmetric Modeling tool has been applied to a curve or surface, the controls will respond to any transformation by also modifying their symmetric partner across the plane of symmetry.

Symmetry plane

The symmetry plane location and axis direction is defined by the layer symmetry plane. By default this plane is defined as Y=0 (XZ plane).
The symmetry plane for each layer can be modified individually by using the Layers > Symmetry > Set Plane tool. Modification of the layer symmetry plane does not affect the symmetry plane currently assigned to each curve or surface.
A symmetry plane is displayed for each object selected.
Once defined, the symmetry plane is unique to each curve or surface. When a curve or surface is transformed, its symmetry plane becomes decoupled from the layer symmetry plane, and follows the object. If the plane doesn’t match the layer symmetry plane anymore, it is drawn in a different color. A confirm box also appears in this case.

Undo

If a curve or surface is modified while establishing symmetric constraint, you can use Edit > Undo ( + Z) to return it to its original state. Similarly, Undo works with any symmetric modification to the controls, up to the limit specified in General Preferences.
You can return a curve or surface to its normal state (without symmetric constraint), while maintaining the modifications to the controls, by removing the construction history with Delete > Delete Construction History, or by using the History View window (Windows > Information > History View).